BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to an exchange coupled film which includes a seed layer, an antiferromagnetic layer, and a ferromagnetic layer deposited in that order from the bottom and in which the magnetization direction of the ferromagnetic layer is pinned in a predetermined direction by an exchange coupling magnetic field produced at the interface between the antiferromagnetic layer and the ferromagnetic layer, and to a magnetic sensing element, such as a spin-valve thin-film element or anisotropic magnetoresistive (AMR) element, using the exchange coupled film. More particularly, the invention relates to an exchange coupled film in which current-carrying reliability (electromigration resistance) and the rate of change in resistance can be appropriately improved even if the recording density is increased, and to a magnetic sensing element using such an exchange coupled film.

[0003] 2. Description of the Related Art

[0004] FIG. 18 is a partial sectional view of a conventional spin-valve thin-film element, viewed from a surface facing a recording medium.

[0005] As shown in FIG. 18 , an antiferromagnetic layer 30 , a pinned magnetic layer 31 , a nonmagnetic interlayer 32 , a free magnetic layer 33 , and a protective layer 7 are deposited in that order on a seed layer 14 which is, for example, composed of a NiFeCr alloy.

[0006] In such a spin-valve thin-film element, an exchange coupling magnetic field is produced at the interface between the antiferromagnetic layer 30 and the pinned magnetic layer 31 by annealing, and the magnetization of the pinned magnetic layer 31 is pinned in the height direction (in the Y direction in the drawing).

[0007] In the spin-valve thin-film element shown in FIG. 18 , hard bias layers 5 are formed at both sides of a laminate including the seed layer 14 to the protective layer 7 , and the magnetization of the free magnetic layer 33 is aligned in the track width direction (in the X direction in the drawing) by a longitudinal bias magnetic field from the hard bias layers 5 .

[0008] As shown in FIG. 18 , electrode layers 8 are disposed on the hard bias layers 5 . Although a sensing current from one of the electrode layers 8 needs to flow through three layers, i.e., the pinned magnetic layer 31 , the nonmagnetic interlayer 32 , and the free magnetic layer 33 , the sensing current is also shunted to the seed layer 14 and the antiferromagnetic layer 30 in this structure.

[0009] By providing the seed layer 14 under the antiferromagnetic layer 30 , the {111} orientations of the individual layers formed on the seed layer 14 are improved, and the crystal grain size in the planar direction of the layers (in the X-Y planar direction) is considered to be increased, and therefore, an improvement in current-carrying reliability, for example, electromigration resistance, an improvement in the rate of change in resistance (ΔR/R), and an improvement in the soft magnetic properties of the free magnetic layer 33 are expected.

[0010] In order to improve the {111} orientations of the individual layers formed on the seed layer 14 and to increase the crystal grain size in the planar direction, the seed layer 14 must have a face-centered cubic structure (fcc structure) and the surface of the seed layer 14 must have satisfactory wettability. If the surface of the seed layer 14 has satisfactory wettability, when the antiferromagnetic layer 30 is deposited on the seed layer 14 by sputtering, the atoms of the antiferromagnetic material constituting the antiferromagnetic layer 30 do not easily aggregate, and the orientation in the planar direction of the antiferromagnetic layer 30 can be more strongly aligned to the {111} plane which is the closest-packed plane.

[0011] Although the higher Cr content in the seed layer 14 is considered to be preferable in order to improve the wettability, if the Cr content becomes excessive, a body-centered cubic structure (bcc structure) starts to appear in the crystal structure in addition to the face-centered cubic structure (fcc structure), and therefore, the {111} orientations of the individual layers on the seed layer 14 are degraded, resulting in a degradation in current-carrying reliability and a decrease in the rate of change in resistance.

[0012] In the known art, by setting the Cr content in the seed layer 14 at 35 atomic percent or less, or at 40 atomic percent or less, the crystal structure of the seed layer 14 is kept in the face-centered cubic structure.

[0013] However, as the recording density is increased, spin-valve thin-film elements are further miniaturized, and thereby the density of the sensing current flowing in the spin-valve thin-film elements is increased. Consequently, electromigration may occur, the rate of change in resistance may be decreased due to an increase in resistance, and noise may occur.

[0014] In order to overcome the problems described above, it is effective to improve the wettability of the surface of the seed layer 14 so that the {111} orientations of the individual layers on the seed layer 14 are further improved, and to increase the crystal grain size in the planar direction so that the electric conductivity is improved. For that purpose, the Cr content in the seed layer 14 must be increased more than which has been conventionally set. However, if the Cr content is set at 35 to 40 atomic percent or more, the body-centered cubic structure (bcc structure) appears in the crystal structure of the seed layer 14 in addition to the face-centered cubic structure.

[0015] If the body-centered cubic structure is mixed with the face-centered cubic structure in the seed layer 14 , the {111} orientations of the individual layers deposited on the seed layer 14 cannot be improved, and the crystal grain size cannot be increased, resulting in a decrease in the electric conductivity. Consequently, it is not possible to produce a spin-valve thin-film element which is suitable for increasing the recording density using the conventional seed layer 14 .

SUMMARY OF THE INVENTION

[0016] Objects of the present invention are to provide an exchange coupled film in which the wettability of a seed layer can be improved while the crystal structure of the seed layer is kept in a face-centered cubic structure by appropriately adjusting the composition and thickness of the seed layer, and thus the current-carrying reliability and the rate of change in resistance can be improved, and to provide a magnetic sensing element using the exchange coupled film.

[0017] Other objects of the present invention are to provide an exchange coupled film having a multi-layered seed layer in which the wettability of the seed layer can be improved while the crystal structure of the seed layer is kept in a face-centered cubic structure by appropriately adjusting the composition and thickness of the seed layer, and thus the current-carrying reliability and the rate of change in resistance can be improved, to provide a magnetic sensing element using the exchange coupled film, to provide a method for making the exchange coupled film, and to provide a method for making the magnetic sensing element.

[0018] In one aspect of the present invention, an exchange coupled film includes a nonmagnetic seed layer, an antiferromagnetic layer, and a ferromagnetic layer deposited in that order from the bottom, the magnetization of the ferromagnetic layer being directed in a predetermined direction by an exchange coupling magnetic field produced at the interface between the antiferromagnetic layer and the ferromagnetic layer. The seed layer contains α and Cr, α being at least one of Fe, Ni, and Co, and the Cr content is 35 to 60 atomic percent. The thickness of the seed layer is 10 to 200 Å, and the crystal structure of the seed layer is a face-centered cubic structure.

[0019] In the exchange coupled film of the present invention, since the Cr content in the seed layer is high at 35 to 60 atomic percent, the wettability at the surface of the seed layer can be improved.

[0020] Wettability is improved when the surface energy increases so that the surface becomes active. In order to improve the wettability, it is important to increase the Cr content in the seed layer. Other important factors are the temperature of the surface of a substrate for forming the seed layer, the distance between the substrate and a target, the Ar pressure, the sputtering rate, etc. in the process of forming the seed layer.

[0021] If the Cr content in the seed layer is low and the surface of the seed layer has unsatisfactory wettability, as shown in FIG. 5 , the atoms sputtered to the surface of the seed layer do not move sufficiently over the surface and easily aggregate to form nuclei. The formation of such nuclei can be observed by an electron microscope.

[0022] When the nuclei are formed and the atoms are deposited so as to form a so-called “island structure”, the orientation in the planar direction (i.e., a direction parallel to the layer surface) of an antiferromagnetic layer formed on the seed layer by sputtering is not easily brought close to the {111} orientation corresponding to the closest-packed plane.

[0023] In contrast, if the Cr content in the seed layer is high and the surface of the seed layer has satisfactory wettability, as shown in FIG. 6 , the atoms sputtered to the surface of the seed layer move sufficiently over the surface and do not aggregate. In such a case, the orientation in the planar direction of an antiferromagnetic layer formed on the seed layer is easily brought close to the {111} orientation corresponding to the closest-packed plane.

[0024] In the present invention, since the surface of the seed layer has satisfactory wettability, the orientations in the planar direction of the individual layers formed on the seed layer can be more strongly aligned to the {111} plane which is the closest-packed plane.

[0025] In the exchange coupled film of the present invention, the crystal structure of the seed layer is a face-centered cubic structure (fcc structure).

[0026] FIG. 9 is a ternary equilibrium diagram of a NiFeCr alloy, which shows the relationships between the contents of the individual elements and the crystal structures of the NiFeCr alloy. As shown in FIG. 9 , in the case of a bulk alloy, a borderline indicated by a dotted chain line extends from a point of 40 atomic percent on the axis of the Cr content in a direction in which the Fe content is increased and the Ni content is decreased. In a zone at the left side of the borderline-in which the Cr content is low, the crystal structure of the NiFeCr alloy is a face-centered cubic structure (fcc structure), and in a zone at the right side of the borderline in which the Cr content is high, a body-centered cubic structure (bcc structure) is also present in the crystal structure of the NiFeCr alloy in addition to the face-centered cubic structure.

[0027] As is obvious from the diagram, when the atomic ratio of Ni to Fe is 8:2, with a Cr content of 35 atomic percent being a borderline, if the Cr content is less than 35 atomic percent, the crystal structure of the NiFeCr alloy only includes the face-centered cubic structure, and if the Cr content is more than 35 atomic percent, the crystal structure of the NiFeCr alloy includes a mixed phase of the face-centered cubic structure and the body-centered cubic structure.

[0028] Strictly speaking, there is a difference in the state between the case of the bulk alloy and the case of a sputtered thin film. In the case of the sputtered thin film, the state may be brought close to the nonequilibrium state. Therefore, even if the body-centered cubic structure is present in addition to the face-centered cubic structure at a certain compositional ratio in the case of the bulk alloy, the sputtered thin film does not necessarily have such a state. In order to adjust the compositional ratio in the sputtered thin film based on the known equilibrium diagram in the case of the bulk alloy, it has been the practice to set the Cr content at 35 atomic percent or less (particularly when the atomic ratio of Ni to Fe is 8:2), or at 40 atomic percent or less, so that the body-centered cubic structure is not mixed in the crystal structure.

[0029] In contrast, in the present invention, the Cr content is high at 35 to 60 atomic percent, and if the equilibrium diagram in the bulk alloy ( FIG. 9 ) is taken into consideration, the crystal structure in this range obviously has a mixture of the face-centered cubic structure and the body-centered cubic structure. However, in the present invention, even in such a range, the crystal structure can be composed of the face-centered cubic structure only. The reason for this is closely related to the thickness of the seed layer.

[0030] In the present invention, the thickness of the seed layer is in the range of 10 to 200 Å. If the thickness of the seed layer is set at more than 200 Å, even if the Cr content is 35 atomic percent, the body-centered cubic structure starts to appear. However, if the thickness of the seed layer is set at 200 Å or less and the Cr content is adjusted within the range of 35 to 60 atomic percent, the crystal structure can be just composed of the face-centered cubic structure.

[0031] This is because the thickness of the seed layer is small. By decreasing the thickness of the seed layer as described above, even in the nonequilibrium state, since the energy is not very high, the equilibrium state occurring in the case of the bulk alloy is unlikely to occur and a metastable state is brought about, and thus the crystal structure can be appropriately kept in the face-centered cubic structure.

[0032] However, as will be described below with reference to a graph, it is necessary to decrease the thickness of the seed layer as the Cr content is increased in order to obtain the metastable state so that the crystal structure is composed of the face-centered cubic structure only.

[0033] Even if the thickness of the seed layer is less than 10 Å, although the crystal structure can be kept in the face-centered cubic structure, since the {111} orientation of the seed layer becomes insufficient, the crystal orientations of the individual layers formed on the seed layer cannot be appropriately {111} oriented. Therefore, the lower limit of the thickness of the seed layer is set at 10 Å in the present invention.

[0034] As described above, in the present invention, by setting the Cr content of the seed layer at 35 to 60 atomic percent, the wettability of the surface of the seed layer is improved, and also, by adjusting the thickness within the range of 10 to 200 Å, the crystal structure of the seed layer can be just composed of the face-centered cubic structure. Consequently, the orientations in the planar direction of the individual layers deposited on the seed layer can be satisfactorily {111} oriented, and the crystal grain size in the planar direction of the layers can be increased.

[0035] As the crystal grain size increases, the resistance decreases, resulting in a decrease in Joule heat. Since the {111} plane which is the closest-packed plane is preferred to be oriented parallel to the layer surface, diffusion does not easily occur between the adjoining layers. As a result, electromigration resistance can be improved and current-carrying reliability can be improved.

[0036] Since the resistance is decreased, electric conductivity is improved, and therefore, in the magnetic sensing element described below, it is possible to improve the rate of change in resistance (ΔR/R), the change in conductivity (ΔG), and the soft magnetic properties of the free magnetic layer.

[0037] In the exchange coupled film of the present invention, preferably, the Cr content is 40 to 60 atomic percent, and the thickness of the seed layer is 10 to 170 Å.

[0038] Preferably, the Cr content is 45 to 60 atomic percent, and the thickness of the seed layer is 10 to 130 Å.

[0039] More preferably, the Cr content is 40 to 50 atomic percent, and the thickness of the seed layer is 10 to 170 Å.

[0040] More preferably, the Cr content is 45 to 55 atomic percent, and the thickness of the seed layer is 10 to 130 Å.

[0041] By setting the Cr content and thickness within the ranges described above, as will be confirmed by testing described below, the rate of change in resistance (ΔR/R) and the change in conductivity (ΔG) can be further improved, the average crystal grain size can be further increased, and the heat resistance temperature can be further improved.

[0042] In each of the preferable Cr contents, by appropriately adjusting the thickness within the range described above, the crystal structure can be just composed of the face-centered cubic structure.

[0043] Preferably, the thickness of the seed layer is 80 Å or less.

[0044] More preferably, the thickness of the seed layer is 60 Å or less.

[0045] By setting the thickness at 80 Å or less, or 60 Å or less, the crystal structure can be just composed of the face-centered cubic structure reliably, and also the shunt loss of the sensing current can be more appropriately decreased.

[0046] In the exchange coupled film of the present invention, preferably, the seed layer is composed of a NiFeCr alloy or a NiCr alloy.

[0047] Preferably, the composition of the seed layer is represented by (Ni _100−x Fe _x )—Cr, and the atomic ratio x satisfies the relationship 0≦x≦70. More preferably, the atomic ratio x satisfies the relationship 0≦x≦50. Most preferably, the atomic ratio x satisfies the relationship 0≦x≦30.

[0048] In the exchange coupled film of the present invention, preferably, an underlayer composed of at least one element selected from the group consisting of Ta, Hf, Nb, Zr, Ti, Mo, and W is formed under the seed-layer. Consequently, the crystal structure of the seed layer can be appropriately set to be the face-centered cubic structure.

[0049] Preferably, the seed layer is formed by sputtering. Consequently, the seed layer does not have the same equilibrium state as that of the bulk alloy, and even if the Cr content is 35 atomic percent or more, a metastable state is formed, and the crystal structure is easily set to be the face-centered cubic structure.

[0050] In the exchange coupled film of the present invention, the average crystal grain size in a direction parallel to the layer surface in each layer formed on the seed layer is preferably 100 Å or more, more preferably, 150 Å or more, and most preferably, 170 Å or more.

[0051] In the exchange coupled film of the present invention, preferably, the grain boundaries formed in the antiferromagnetic layer and the grain boundaries formed in the ferromagnetic layer which appear in a cross section of the exchange coupled film parallel to the thickness direction are at least partially discontinuous at the interface between the antiferromagnetic layer and the ferromagnetic layer.

[0052] In the exchange coupled film of the present invention, preferably, the grain boundaries formed in the antiferromagnetic layer and the grain boundaries formed in the seed layer which appear in a cross section of the exchange coupled film parallel to the thickness direction are at least partially discontinuous at the interface between the antiferromagnetic layer and the seed layer.

[0053] In the exchange coupled film of the present invention, preferably, equivalent crystal planes represented as {111} planes in the antiferromagnetic layer and the ferromagnetic layer are preferentially oriented as crystal planes parallel to the interface between the antiferromagnetic layer and the ferromagnetic layer, and at least some of the equivalent crystal axes in the crystal planes are directed in different directions between the antiferromagnetic layer and the ferromagnetic layer.

[0054] In the exchange coupled film of the present invention, preferably, equivalent crystal planes represented as {111} planes in the antiferromagnetic layer and the seed layer are preferentially oriented as crystal planes parallel to the interface between the antiferromagnetic layer and the seed layer, and at least some of the equivalent crystal axes in the crystal planes are directed in different directions between the antiferromagnetic layer and the seed layer.

[0055] Preferably, the antiferromagnetic layer is composed of X and Mn, where X is at least one element selected from the group consisting of Pt, Pd, Ir, Rh, Ru, and Os.

[0056] The antiferromagnetic layer may be composed of an X—Mn—X′ alloy, where X′ is at least one element selected from the group consisting of Ne, Ar, Kr, Xe, Be, B, C, N, Mg, Al, Si, P, Ti, V, Cr, Fe, Co, Ni, Cu, Zn, Ga, Ge, Zr, Nb, Mo, Ag, Cd, Ir, Sn, Hf, Ta, W, Re, Au, Pb, and rare-earth elements.

[0057] In such a case, preferably, the X—Mn—X′ alloy is either an interstitial solid solution in which atoms of X′ enter interstices in a space lattice composed of X and Mn or a substitutional solid solution in which atoms of X′ are substituted for some atoms at the lattice points of a crystal lattice composed of X and Mn.

[0058] Preferably, the X content or the X+X′ content is 45 to 60 atomic percent.

[0059] In another aspect of the present invention, a magnetic sensing element includes a seed layer, an antiferromagnetic layer, a pinned magnetic layer, a nonmagnetic interlayer, and a free magnetic layer deposited in that order from the bottom, the magnetization of the free magnetic layer being aligned in a direction substantially perpendicular to the magnetization direction of the pinned magnetic layer. The seed layer, the antiferromagnetic layer, and the pinned magnetic layer constitute the exchange coupled film described above.

[0060] In another aspect of the present invention, a magnetic sensing element includes a seed layer, an antiferromagnetic exchange bias layer, a free magnetic layer, a nonmagnetic interlayer, a pinned magnetic layer, and an antiferromagnetic layer deposited in that order from the bottom, the magnetization of the free magnetic layer being aligned in a direction substantially perpendicular to the magnetization direction of the pinned magnetic layer. The seed layer, the exchange bias layer, and the free magnetic layer constitute the exchange coupled film described above.

[0061] In another aspect of the present invention, a magnetic sensing element includes a free magnetic layer; an upper nonmagnetic interlayer disposed over the free magnetic layer; a lower nonmagnetic interlayer disposed under the free magnetic layer; an upper pinned magnetic layer disposed over the upper nonmagnetic interlayer; a lower pinned magnetic layer disposed under the lower nonmagnetic interlayer; an upper antiferromagnetic layer disposed over the upper pinned magnetic layer; a lower antiferromagnetic layer disposed under the lower pinned magnetic layer; and a seed layer disposed under the lower antiferromagnetic layer, the magnetization of the free magnetic layer being aligned in a direction substantially perpendicular to the magnetization direction of the pinned magnetic layers. The seed layer, the lower antiferromagnetic layer, and the lower pinned magnetic layer constitute the exchange coupled film described above.

[0062] In another aspect of the present invention, a magnetic sensing element includes a seed layer, an antiferromagnetic exchange bias layer, a magnetoresistive layer, a nonmagnetic layer, and a soft magnetic layer deposited in that order from the bottom. The seed layer, the exchange bias layer, and the magnetoresistive layer constitute the exchange coupled film described above.

[0063] Since the exchange coupled films are used in the magnetic sensing elements, electromigration resistance and current-carrying reliability can be improved. Furthermore, the rate of change in resistance (ΔR/R) can be improved, and thermal noise can be reduced.

[0064] Moreover, it is possible to decrease the in-plane crystal magnetic anisotropy energy K when the magnetization rotates in the free magnetic layer or the magnetoresistive layer. Consequently, the coercive force Hc which is proportional to the in-plane crystal magnetic anisotropy energy K can also be decreased, and the magnetization of the free magnetic layer can be rotated with good sensitivity to an external magnetic field.

[0065] In the present invention, even if magnetic sensing elements are further miniaturized as the recording density is increased, the effects described above can be appropriately achieved, and it is possible to produce magnetic sensing elements suitable for increasing the recording density.

[0066] In another aspect of the present invention, an exchange coupled film includes a nonmagnetic or partially ferromagnetic seed layer, an antiferromagnetic layer, and a ferromagnetic layer deposited in that order from the bottom, the magnetization of the ferromagnetic layer being directed in a predetermined direction by an exchange coupling magnetic field produced at the interface between the antiferromagnetic layer and the ferromagnetic layer. The seed layer contains α and Cr, α being at least one of Fe, Ni, and Co. The Cr content at the interface with the antiferromagnetic layer is 40 atomic percent or more and is higher than the Cr content at another surface of the seed layer opposite to the antiferromagnetic layer. The seed layer has a region in which the Cr content gradually increases toward the antiferromagnetic layer. The crystal structure of the seed layer at the interface with the antiferromagnetic layer is a face-centered cubic structure.

[0067] In the exchange coupled film of the present invention, since the Cr content at the interface with the antiferromagnetic layer is 40 atomic percent or more, the wettability at the surface of the seed layer can be improved.

[0068] Wettability is improved when the surface energy increases so that the surface becomes active. In order to improve the wettability, it is important to increase the Cr content in the seed layer. Other important factors are the temperature of the surface of a substrate for forming the seed layer, the distance between the substrate and a target, the Ar pressure, the sputtering rate, etc., in the process of forming the seed layer.

[0069] If the Cr content in the seed layer is low and the surface of the seed layer has unsatisfactory wettability, as shown in FIG. 5 , the atoms sputtered to the surface of the seed layer do not move sufficiently over the surface and easily aggregate to form nuclei. The formation of such nuclei can be observed by an electron microscope.

[0070] When the nuclei are formed and the atoms are deposited so as to form a so-called “island structure”, the orientation in the planar direction (i.e., a direction parallel to the layer surface) of an antiferromagnetic layer formed on the seed layer by sputtering is not easily brought close to the {111} orientation corresponding to the closest-packed plane.

[0071] In contrast, if the Cr content in the seed layer is high and the surface of the seed layer has satisfactory wettability, as shown in FIG. 6 , the atoms sputtered to the surface of the seed layer move sufficiently over the surface and do not aggregate. In such a case, the orientation in the planar direction of an antiferromagnetic layer formed on the seed layer is easily brought close to the {111} orientation corresponding to the closest-packed plane.

[0072] In the present invention, since the surface of the seed layer has satisfactory wettability, the orientations in the planar direction of the individual layers formed on the seed layer can be more strongly aligned to the {111} plane which is the closest-packed plane.

[0073] In the exchange coupled film of the present invention, the crystal structure of the seed layer at the interface with the antiferromagnetic layer is a face-centered cubic structure (fcc structure). In the present invention, even if the Cr content at the surface of the seed layer is 40 atomic percent or more, the crystal structure can be just composed of the face-centered cubic structure. This is because the seed layer has the region in which the Cr content gradually increases toward the antiferromagnetic layer, and the Cr content of the seed layer at the surface opposite to the antiferromagnetic layer is smaller than the Cr content of the seed layer at the interface with the antiferromagnetic layer.

[0074] In order to produce a so-called “composition gradient”, as will be described below with reference to a production method, the seed layer is formed so as to have a layered structure including an upper sublayer and a lower sublayer, and the Cr content in the lower sublayer is set to be lower than the Cr content in the upper sublayer. In the lower sublayer with the lower Cr content, the face-centered cubic structure can be satisfactorily maintained. On the other hand, in the upper sublayer deposited on the lower sublayer, even if the Cr content is 40 atomic percent or more, the face-centered cubic structure is easily formed under the influence of the crystal structure of the lower sublayer, and the crystal structure can be just composed of the face-centered cubic structure without a body-centered cubic structure in spite of a Cr content of 40 atomic percent or more. However, it is important to decrease the thickness of the upper sublayer, and for example, the thickness of the upper sublayer is set at 20 Å or less. Since the thickness of the upper sublayer is decreased, the crystal structure of the upper sublayer is influenced by the crystal structure of the lower sublayer as an underlayer. The equilibrium state occurring in the case of the bulk alloy is unlikely to occur and a metastable state is brought about, and thus the crystal structure can be appropriately kept in the face-centered cubic structure.

[0075] After the upper sublayer and the lower sublayer are formed as described above, annealing is performed in order to produce an exchange coupling magnetic field between the antiferromagnetic layer and the ferromagnetic layer. By the annealing treatment, diffusion may occur between the upper sublayer and the lower sublayer, resulting in a substantially single seed layer including the upper sublayer and the lower sublayer. In such a case, the compositional analysis of the seed layer shows that the seed layer has a region in which the Cr content (at %) gradually increases toward the antiferromagnetic layer and the Cr content of the seed layer at the surface opposite to the antiferromagnetic layer is smaller than the Cr content of the seed layer at the interface with the antiferromagnetic layer.

[0076] As described above, in the present invention, since the Cr content of the seed layer at the interface with the antiferromagnetic layer is 40 atomic percent or more, the wettability is improved, and also, since the crystal structure of the seed layer at the interface with the antiferromagnetic layer is the face-centered cubic structure, the orientations in the planar direction of the individual layers deposited on the seed layer can be satisfactorily {111} oriented, and the crystal grain size in the planar direction of the layers can be increased.

[0077] As the crystal grain size increases, the resistance decreases, resulting in a decrease in Joule heat. Since the {111} plane which is the closest-packed plane is preferentially oriented parallel to the layer surface, diffusion does not easily occur between the adjoining layers. As a result, electromigration resistance can be improved and current-carrying reliability can be improved.

[0078] Since the resistance is decreased, electric conductivity is improved, and therefore, in the magnetic sensing element described below, it is possible to improve the rate of change in resistance (ΔR/R), the change in conductivity (ΔG), and the soft magnetic properties of the free magnetic layer. Thermal noise can also be reduced.

[0079] In the exchange coupled film of the present invention, preferably, the Cr content of the seed layer at the interface with the antiferromagnetic layer is 40 to 70 atomic percent, and more preferably, 45 to 60 atomic percent.

[0080] In the exchange coupled film of the present invention, preferably, the Cr content of the seed layer at the surface opposite to the antiferromagnetic layer is 20 to 45 atomic percent, and more preferably, 20 to 40 atomic percent.

[0081] In the exchange coupled film of the present invention, preferably, the seed layer is composed of a NiFeCr alloy or a NiCr alloy.

[0082] Preferably, the composition of the seed layer is represented by (Ni _100−x Fe _x )—Cr, and the atomic ratio x satisfies the relationship 0≦x≦70. More preferably, the atomic ratio x satisfies the relationship 0≦x≦50. Most preferably, the atomic ratio x satisfies the relationship 0≦x≦30.

[0083] In the exchange coupled film of the present invention, preferably, the thickness of the seed layer is 23 to 80 Å, and more preferably, 25 to 50 Å.

[0084] In another aspect of the present invention, an exchange coupled film includes a nonmagnetic or partially ferromagnetic seed layer, an antiferromagnetic layer, and a ferromagnetic layer deposited in that order from the bottom, the magnetization of the ferromagnetic layer being directed in a predetermined direction by an exchange coupling magnetic field produced at the interface between the antiferromagnetic layer and the ferromagnetic layer. The seed layer has a layered structure including a nonmagnetic or partially ferromagnetic upper sublayer and a nonmagnetic or partially ferromagnetic lower sublayer, each containing α and Cr, α being at least one of Fe, Ni, and Co. The Cr content in the upper sublayer is 40 atomic percent or more, and the crystal structure at the interface with the antiferromagnetic layer is a face-centered cubic structure. The Cr content in the upper sublayer is higher than the Cr content in the lower sublayer, and the thickness of the upper sublayer is smaller than the thickness of the lower sublayer.

[0085] This exchange coupled film has the same structure as that of the exchange coupled film previously described apart from the fact that this exchange coupled film has a seed layer with a two-layered structure while the seed layer of the previously described exchange coupled film has a single-layered structure, and the same effects can be achieved.

[0086] That is, in the seed layer of this exchange coupled film, the lower sublayer, which has a lower Cr content than the upper sublayer, appropriately maintains the face-centered cubic structure, and the upper sublayer, which has a Cr content of 40 atomic percent or more, has the face-centered cubic structure. Therefore, the orientations in the planar direction of the individual layers deposited on the seed layer can be satisfactorily {111} oriented, and the crystal grain size in the planar direction of the layers can be increased.

[0087] Consequently, electromigration resistance can be improved and current-carrying reliability can be improved. In the magnetic sensing element described below, it is possible to improve the rate of change in resistance (ΔR/R), the change in conductivity (ΔG), and the soft magnetic properties of the free magnetic layer.

[0088] In the exchange coupled film of the present invention, preferably, the Cr content of the upper sublayer is 40 to 70 atomic percent, and more preferably, 45 to 60 atomic percent.

[0089] In the exchange coupled film of the present invention, preferably, the Cr content of the lower sublayer is 20 to 45 atomic percent, and more preferably, 20 to 40 atomic percent.

[0090] Preferably, each of the upper sublayer and the lower sublayer is composed of a NiFeCr alloy or a NiCr alloy.

[0091] Preferably, the composition of each of the upper sublayer and the lower sublayer is represented by (Ni _100−x Fe _x )—Cr, and the atomic ratio x satisfies the relationship 0≦x≦70. More preferably, the atomic ratio x satisfies the relationship 0≦x≦50. Most preferably, the atomic ratio x satisfies the relationship 0≦x≦30.

[0092] The lower sublayer may be composed of a NiFe alloy.

[0093] Preferably, the thickness of the upper sublayer is 3 to 20 Å, and more preferably, 5 to 10 Å.

[0094] Preferably, the thickness of the lower sublayer is 20 to 60 Å, and more preferably, 20 to 40 Å.

[0095] In the exchange coupled film of the present invention, at least one nonmagnetic or partially ferromagnetic intermediate sublayer may be formed between the upper sublayer and the lower sublayer, and preferably, the intermediate sublayer contains α and Cr, α being at least one of Fe, Ni, and Co, the Cr content of the intermediate sublayer being lower than the Cr content of the upper sublayer.

[0096] In the exchange coupled film of the present invention, preferably, an underlayer composed of at least one element selected from the group consisting of Ta, Hf, Nb, Zr, Ti, Mo, and W is formed under the seed layer. Consequently, the crystal structure of the seed layer can be appropriately set to be the face-centered cubic structure.

[0097] Preferably, the seed layer is formed by sputtering. Consequently, the seed layer does not have the same equilibrium state as that of the bulk alloy, and even if the Cr content is 40 atomic percent or more, a metastable state is formed, and the crystal structure is easily set to be the face-centered cubic structure.

[0098] In the exchange coupled film of the present invention, preferably, the average crystal grain size in a direction parallel to the layer surface in each layer formed on the seed layer is 100 Å or more, and more preferably, 150 Å or more.

[0099] In the exchange coupled film of the present invention, preferably, the grain boundaries formed in the antiferromagnetic layer and the grain boundaries formed in the ferromagnetic layer which appear in a cross section of the exchange coupled film parallel to the thickness direction are at least partially discontinuous at the interface between the antiferromagnetic layer and the ferromagnetic layer.

[0100] In the exchange coupled film of the present invention, preferably, the grain boundaries formed in the antiferromagnetic layer and the grain boundaries formed in the seed layer which appear in a cross section of the exchange coupled film parallel to the thickness direction are at least partially discontinuous at the interface between the antiferromagnetic layer and the seed layer.

[0101] In the exchange coupled film of the present invention, preferably, equivalent crystal planes represented as {111} planes in the antiferromagnetic layer and the ferromagnetic layer are preferentially oriented as crystal planes parallel to the interface between the antiferromagnetic layer and the ferromagnetic layer, and at least some of the equivalent crystal axes in the crystal planes are directed in different directions between the antiferromagnetic layer and the ferromagnetic layer.

[0102] In the exchange coupled film of the present invention, preferably, equivalent crystal planes represented as {111} planes in the antiferromagnetic layer and the seed layer are preferentially oriented as crystal planes parallel to the interface between the antiferromagnetic layer and the seed layer, and at least some of the equivalent crystal axes in the crystal planes are directed in different directions between the antiferromagnetic layer and the seed layer.

[0103] Preferably, the antiferromagnetic layer is composed of X and Mn, where X is at least one element selected from the group consisting of Pt, Pd, Ir, Rh, Ru, and Os.

[0104] The antiferromagnetic layer may be composed of an X—Mn—X′ alloy, where X′ is at least one element selected from the group consisting of Ne, Ar, Kr, Xe, Be, B, C, N, Mg, Al, Si, P, Ti, V, Cr, Fe, Co, Ni, Cu, Zn, Ga, Ge, Zr, Nb, Mo, Ag, Cd, Ir, Sn, Hf, Ta, W, Re, Au, Pb, and rare-earth elements.

[0105] In such a case, preferably, the X—Mn—X′ alloy is either an interstitial solid solution in which atoms of X′ enter interstices in a space lattice composed of X and Mn or a substitutional solid solution in which atoms of X′ are substituted for some atoms at the lattice points of a crystal lattice composed of X and Mn.

[0106] Preferably, the X content or the X+X′ content is 45 to 60 atomic percent.

[0107] In another aspect of the present invention, a magnetic sensing element includes a seed layer, an antiferromagnetic layer, a pinned magnetic layer, a nonmagnetic interlayer, and a free magnetic layer deposited in that order from the bottom, the magnetization of the free magnetic layer being aligned in a direction substantially perpendicular to the magnetization direction of the pinned magnetic layer. The seed layer, the antiferromagnetic layer, and the pinned magnetic layer constitute the exchange coupled film described above.

[0108] In another aspect of the present invention, a magnetic sensing element includes a seed layer, an antiferromagnetic exchange bias layer, a free magnetic layer, a nonmagnetic interlayer, a pinned magnetic layer, and an antiferromagnetic layer deposited in that order from the bottom, the magnetization of the free magnetic layer being aligned in a direction substantially perpendicular to the magnetization direction of the pinned magnetic layer. The seed layer, the exchange bias layer, and the free magnetic layer constitute the exchange coupled film described above.

[0109] In another aspect of the present invention, a magnetic sensing element includes a free magnetic layer; an upper nonmagnetic interlayer disposed over the free magnetic layer; a lower nonmagnetic interlayer disposed under the free magnetic layer; an upper pinned magnetic layer disposed over the upper nonmagnetic interlayer; a lower pinned magnetic layer disposed under the lower nonmagnetic interlayer; an upper antiferromagnetic layer disposed over the upper pinned magnetic layer; a lower antiferromagnetic layer disposed under the lower pinned magnetic layer; and a seed layer disposed under the lower antiferromagnetic layer, the magnetization of the free magnetic layer being aligned in a direction substantially perpendicular to the magnetization direction of the pinned magnetic layers. The seed layer, the lower antiferromagnetic layer, and the lower pinned magnetic layer constitute the exchange coupled film described above.

[0110] In another aspect of the present invention, a magnetic sensing element includes a seed layer, an antiferromagnetic exchange bias layer, a magnetoresistive layer, a nonmagnetic layer, and a soft magnetic layer deposited in that order from the bottom. The seed layer, the exchange bias layer, and the magnetoresistive layer constitute the exchange coupled film described above.

[0111] Since the exchange coupled films are used in the magnetic sensing elements, electromigration resistance and current-carrying reliability can be improved. Furthermore, the rate of change in resistance (ΔR/R) can be improved, and thermal noise can be reduced.

[0112] Moreover, it is possible to decrease the coercive force Hc of the free magnetic layer or the magnetoresistive layer. Consequently, the in-plane crystal magnetic anisotropy energy K which is proportional to the coercive force Hc can also be decreased, and the magnetization of the free magnetic layer can be rotated with good sensitivity to an external magnetic field.

[0113] In the present invention, even if magnetic sensing elements are further miniaturized as the recording density is increased, the effects described above can be appropriately achieved, and it is possible to produce magnetic sensing elements suitable for increasing the recording density.

[0114] In another aspect of the present invention, a first method for making an exchange coupled film, which includes a seed layer, an antiferromagnetic layer, and a ferromagnetic layer deposited in that order from the bottom, the magnetization of the ferromagnetic layer being directed in a predetermined direction by an exchange coupling magnetic field produced at the interface between the antiferromagnetic layer and the ferromagnetic layer, includes:

[0115] step (A) of forming a lower sublayer of the seed layer by sputtering at a thickness of 20 to 60 Å, the lower sublayer being composed of a NiFeCr alloy or NiCr alloy with a Cr content of 20 to 45 atomic percent;

[0116] step (B) of forming an upper sublayer of the seed layer on the lower sublayer by sputtering at a thickness of 3 to 20 Å, the upper sublayer being composed of a NiFeCr alloy or NiCr alloy with a higher Cr content than the lower sublayer and with a Cr content of 40 to 70 atomic percent; and

[0117] step (C) of depositing the antiferromagnetic layer and the ferromagnetic layer in that order on the seed layer, and performing annealing treatment to produce the exchange coupling magnetic field at the interface between the antiferromagnetic layer and the ferromagnetic layer so that the ferromagnetic layer is magnetized in the direction of the magnetic field.

[0118] In step (A), the lower sublayer composed of the NiFeCr alloy or NiCr alloy with a Cr content of 20 to 45 atomic percent is formed by sputtering at a thickness of 20 to 60 Å.

[0119] By setting the Cr content at 20 to 45 atomic percent, the crystal structure of the lower sublayer can be the face-centered cubic structure (fcc structure) appropriately. By setting the thickness of the lower sublayer at a certain level, the crystal structure of the lower sublayer can be the face-centered cubic structure appropriately. However, if the thickness is too large, the amount of the sensing current shunted to the lower sublayer is increased and the body-centered cubic structure is easily mixed in the crystal structure. In this method, the Cr content in the lower sublayer may be 40 to 45 atomic percent. It has been described that, if the Cr content exceeds 40 atomic percent, the body-centered cubic structure starts to be mixed in the crystal structure. However, by decreasing the thickness of the lower sublayer as small as possible, even if the Cr content is 40 atomic percent or more in which the body-centered cubic structure is mixed in the case of the bulk alloy, since energy is not very high, a metastable state is formed, and thus the crystal structure can be just composed of the face-centered cubic structure. From this viewpoint, the thickness of the lower sublayer is set at 20 to 60 Å. Additionally, if an underlayer formed of Ta or the like is placed under the lower sublayer, the crystal structure of the lower sublayer can be just composed of the face-centered cubic structure more appropriately, and the {111} orientation can be improved.

[0120] In step (B), the upper sublayer composed of the NiFeCr alloy or NiCr alloy with a higher Cr content than the lower sublayer and with a Cr content of 40 to 70 atomic percent is formed on the lower sublayer by sputtering at a thickness of 3 to 20 Å.

[0121] By setting the Cr content at 40 to 70 atomic percent, the wettability at the surface of the upper sublayer can be improved.

[0122] Moreover, in the method of the present invention, since the thickness of the upper sublayer is significantly small at 3 to 20 Å, the crystal structure of the upper sublayer is influenced by the crystal structure of the lower sublayer. Since the upper sublayer is formed by sputtering, the equilibrium state occurring in the case of the bulk alloy is unlikely to occur and a metastable state is brought about, and thus the crystal structure of the upper sublayer can be the face-centered cubic structure even if the Cr content is 40 atomic percent or more.

[0123] In step (C), the antiferromagnetic layer and the ferromagnetic layer are formed on the upper sublayer by sputtering. As described above, since the upper sublayer of the seed layer has a surface with improved wettability and the face-centered cubic structure, the orientations in the planar direction of the antiferromagnetic layer and the ferromagnetic layer can be brought closer to the {111} orientation corresponding to the closest-packed plane, and the crystal grain size in the planar direction can be increased.

[0124] As described above, the wettability of the surface of the seed layer can be improved reliably by a simple method, and the crystal structure of the seed layer can be kept in the face-centered cubic structure.

[0125] In the method of the present invention, preferably, the Cr content of the upper sublayer is 45 to 60 atomic percent.

[0126] Preferably, the thickness of the upper sublayer is 5 to 10 Å.

[0127] Preferably, the Cr content of the lower sublayer is 20 to 40 atomic percent.

[0128] Preferably, the composition of each of the upper sublayer and the lower sublayer is represented by (Ni _100−x Fe _x )—Cr, and the atomic ratio x satisfies the relationship 0≦x≦70. More preferably, the atomic ratio x satisfies the relationship 0≦x≦50. Most preferably, the atomic ratio x satisfies the relationship 0 23 x≦30.

[0129] The method of the present invention may include, in place of step (A), step (D) of forming a lower sublayer of the seed layer by sputtering at a thickness of 20 to 60 Å, the lower sublayer being composed of a NiFe alloy.

[0130] The lower sublayer of the seed layer may be composed of the NiFe alloy which does not contain Cr. Since Cr is not contained, the crystal structure of the lower sublayer can be easily and reliably set to be the face-centered cubic structure.

[0131] Preferably, the thickness of the lower sublayer is 20 to 40 Å.

[0132] In another aspect of the present invention, a second method for making an exchange coupled film, which includes a seed layer, an antiferromagnetic layer, and a ferromagnetic layer deposited in that order from the bottom, the magnetization of the ferromagnetic layer being directed in a predetermined direction by an exchange coupling magnetic field produced at the interface between the antiferromagnetic layer and the ferromagnetic layer, includes:

[0133] step (E) of forming the seed layer composed of a NiFeCr alloy or NiCr alloy by sputtering at a thickness of 23 to 80 Å so that the Cr content gradually increases from the lower surface to the upper surface of the seed layer, with a Cr content at the lower surface of 20 to 45 atomic percent and with a Cr content at the upper surface of 40 to 70 atomic percent; and

[0134] step (F) of depositing the antiferromagnetic layer and the ferromagnetic layer in that order on the seed layer, and performing annealing treatment to produce the exchange coupling magnetic field at the interface between the antiferromagnetic layer and the ferromagnetic layer so that the ferromagnetic layer is magnetized in the direction of the magnetic field.

[0135] In the second method, unlike the first method previously described, the seed layer does not have a two-layered structure, and the seed layer is formed by sputtering as a single layer. In such a case, sputtering is performed so that the Cr content gradually increases from the lower surface to the upper surface of the seed layer. For that purpose, for example, a NiFe target and a Cr target are prepared and sputtering is performed while the electric power supplied to the Cr target is gradually increased as the thickness increases.

[0136] In this method, the wettability of the surface of the seed layer can also be improved reliably by a simple method, and the crystal structure of the seed layer can be kept in the face-centered cubic structure.

[0137] Preferably, the composition of the seed layer is represented by (Ni _100−x Fe _x )—Cr, and the atomic ratio x satisfies the relationship 0≦x≦70. More preferably, the atomic ratio x satisfies the relationship 0≦x≦50. Most preferably, the atomic ratio x satisfies the relationship 0≦x≦30.

[0138] Preferably, the seed layer is formed by sputtering at a thickness of 25 to 50 Å.

[0139] Preferably, an underlayer composed of at least one element selected from the group consisting of Ta, Hf, Nb, Zr, Ti, Mo, and W is formed under the seed layer. Consequently, the crystal structure of the seed layer can be the face-centered cubic structure more reliably, and the preferred orientation of the {111} plane can be improved.

[0140] Preferably, the antiferromagnetic layer is formed by sputtering using an antiferromagnetic material containing X and Mn, where X is at least one element selected from the group consisting of Pt, Pd, Ir, Rh, Ru, and Os.

[0141] The antiferromagnetic layer may be formed by sputtering using an X—Mn—X′ alloy, where X′ is at least one element selected from the group consisting of Ne, Ar, Kr, Xe, Be, B, C, N, Mg, Al, Si, P, Ti, V, Cr, Fe, Co, Ni, Cu, Zn, Ga, Ge, Zr, Nb, Mo, Ag, Cd, Ir, Sn, Hf, Ta, W, Re, Au, Pb, and rare-earth elements.

[0142] Preferably, the X content or the X+X′ content is 45 to 60 atomic percent.

[0143] In another aspect of the present invention, a method for making a magnetic sensing element includes depositing a seed layer, an antiferromagnetic layer, a pinned magnetic layer, a nonmagnetic interlayer, and a free magnetic layer in that order from the bottom, in which the exchange coupled film described above is used for the seed layer, the antiferromagnetic layer, and the pinned magnetic layer.

[0144] In another aspect of the present invention, a method for making a magnetic sensing element includes depositing a seed layer, an antiferromagnetic exchange bias layer, a free magnetic layer, a nonmagnetic interlayer, a pinned magnetic layer, and an antiferromagnetic layer in that order from the bottom, in which the exchange coupled film described above is used for the seed layer, the exchange bias layer, and the free magnetic layer.

[0145] In another aspect of the present invention, a method for making a magnetic sensing element includes depositing a seed layer, a lower antiferromagnetic layer, a lower pinned magnetic layer, a lower nonmagnetic interlayer, a free magnetic layer, an upper nonmagnetic interlayer, an upper pinned magnetic layer, an upper antiferromagnetic layer, in which the exchange coupled film described above is used for the seed layer, the lower antiferromagnetic layer, and the lower pinned magnetic layer.

[0146] In another aspect of the present invention, a method for making a magnetic sensing element includes depositing a seed layer, an antiferromagnetic exchange bias layer, a magnetoresistive layer, a nonmagnetic layer, and a soft magnetic layer, in which the exchange coupled film described above is used for the seed layer, the exchange bias layer, and the magnetoresistive layer.

[0147] In either method for making a magnetic sensing element, the wettability of the seed layer can be improved reliably by a simple method, and the crystal structure of the seed layer can be kept in the face-centered cubic structure.

[0148] Consequently, the orientations in the planar direction of the individual layers formed on the seed layer can be satisfactorily brought close to the {111} orientation corresponding to the closest-packed plane, and the crystal grain size in the planar direction of the layers can be increased.

[0149] Therefore, in the present invention, it is possible to produce magnetic sensing elements suitable for increasing the recording density in which current-carrying reliability, such as electromigration resistance, the rate of change in resistance, and the soft magnetic properties of free magnetic layers can be appropriately improved.