DESCRIPTION OF THE PREFERRED EMBODIMENT

[0101] FIG. 1 is a cross section of the structure of the magnetic sensing element (single spin-valve type magnetoresistive element) in a first embodiment of the present invention viewed from an opposed face side to a recording medium. Only the cross section of the central portion of the element elongating in the X-direction is shown in FIG. 1 .

[0102] The single spin-valve type magnetoresistive element is provided at the end of a trailing side of a floating type slider attached in a hard disk device to sense a recording magnetic field on the hard disk. The travel direction of a magnetic recording device such as the hard disk is in the Z-direction, and the direction of a leak magnetic field from the magnetic recording medium is in the Y-direction.

[0103] An underlayer 6 comprising a nonmagnetic material such as one or plural elements of Ta, Hf, Nb, Zr, Ti, Mo and W is formed at the lowermost part in FIG. 1 . A seed layer 22 , an antiferromagnetic layer 4 , a pinned magnetic layer 3 , a nonmagnetic layer 2 and a free magnetic layer 1 are laminated on the seed layer 6 .

[0104] The antiferromagnetic layer 4 is preferably formed of an antiferromagnetic material comprising an element X (X denotes one or plural elements of Pt, Pd, Ir, Rh, Ru and Os) and Mn on the seed layer 22 .

[0105] The X—Mn alloy using these platinum group elements has excellent characteristics as the antiferromagnetic material such as an excellent in corrosion resistance, a high blocking temperature and an ability for increasing an exchange coupling magnetic field (Hex). It is particularly preferable to use Pt among the platinum group elements, and a binary alloy such as a PtMn alloy may be used.

[0106] The antiferromagnetic layer 4 may be formed with an antiferromagnetic material comprising an element X, element X′ (the element X′ denotes one or plural elements 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, Pt and rare earth elements) and Mn.

[0107] It is preferable to use an element that forms an invasion type solid solution by invading in interstices of a space lattice comprising the element X and Mn, or an element that forms a substitution type element by substituting a part of the lattice point of a crystal lattice comprising the element X and Mn, for the element X′. The solid solution as used herein refers to as a solid in which the components are uniformly mixed over a wide range.

[0108] Forming the invasion type or substitution type solid solution permits the lattice constant of the X—Mn—X′ alloy to be larger than the lattice constant of the X—Mn alloy. Accordingly, the difference of the lattice constant between the antiferromagnetic layer 4 and pinned magnetic layer 3 may be expanded to allow the interface structure between the antiferromagnetic layer 4 and pinned magnetic layer 3 to be readily put in a non-coherent state. The non-coherent state as used herein mans a state in which the atoms constituting the antiferromagnetic layer 4 do not correspond to the atoms constituting the pinned magnetic layer 3 in a 1:1 relation at the interface between the antiferromagnetic layer 4 and pinned magnetic layer 3 .

[0109] When the element X′ that forms the substitution type solid solution is used, too much composition ratio of the element X′ makes the antiferromagnetic layer to have decreased antiferromagnetic characteristics, thereby reducing the exchange coupling magnetic field generated at the interface on the pinned magnetic layer 3 . It is particularly preferable in the present invention to use a rare gas element (one or plural elements of Ne, Ar, Kr and Xe) as an inert gas as the element X′. Since the rare gas element is inert, the antiferromagnetic characteristics are not so largely affected by adding the rare gas element in the layer. Moreover, since Ar has been introduced in a sputtering apparatus as a sputtering gas, Ar may readily invade in the layer merely by properly adjusting the gas pressure.

[0110] Although the element X′ cannot be hardly incorporated in the layer when a gaseous element is used for the element X′, the exchange coupling magnetic field generated by the heat treatment can be markedly increased merely by allowing a minute amount of the element to invade in the layer when the rare gas is used.

[0111] The composition range of the element X′ is preferably 0.2 to 10 at %, more preferably 0.5 to 5 at % in the present invention. The element X is preferably Pt, and the Pt—Mn—X′ alloy is used in the present invention.

[0112] The element X or elements X+X′ in the antiferromagnetic layer 4 is preferably determined to be 45 at % or more and 60 at % or less, more preferably 49 at % to 56.5 at %, in the present invention. The composition ratio above permits the non-coherent state to be attained at the interface on the pinned magnetic layer 3 in the film deposition process. The antiferromagnetic layer 4 is supposed to perform a proper ordering transformation by applying the heat treatment.

[0113] The pinned magnetic layer 3 formed on the antiferromagnetic layer 4 comprises a five-layered structure.

[0114] The pinned magnetic layer 3 comprises a magnetic layer 11 , an intermediate layer 12 , a magnetic layer 13 , a specular reflection layer 16 and a magnetic layer 23 . The direction of magnetization of the magnetic layers 11 , 13 and 23 are put into an antiparallel state with each other by an exchange coupling magnetic field at the interface on the antiferromagnetic layer 4 and by an antiferromagnetic exchange coupling magnetic field (RKKY mutual interaction) with intervention of the intermediate layer 12 . This antiparallel state is called as an artificial ferrimagnetic coupling state, which permits magnetization of the pinned magnetic layer 3 to be stabilized while apparently increasing the exchange coupling magnetic field generated at the interface between the pinned magnetic field and antiferromagnetic layer 4 . The magnetic layer 13 is magnetized in the same direction as the magnetic layer 23 .

[0115] A specular reflection layer 16 is formed between the magnetic layers 13 and 23 in this embodiment. Providing the specular reflection layer 16 permits up-spin conduction electrons of the conduction electrons moving in the nonmagnetic layer 2 by flowing a sense current to be reflected at the boundary between the specular reflection layer 16 and magnetic layer 23 while maintaining the spin direction. Consequently, the mean free path of the up-spin conduction electrons may be expanded to enable the difference between the mean free paths of the up-spin conduction electrons and down-spin conduction electrons to be increased, thereby enhancing the rate of change of resistance (ΔR/R).

[0116] The surface of the magnetic layer 13 is oxidized after forming the magnetic layer 13 , and the oxidized surface thereof serves as the specular reflection layer 16 . For example, the magnetic layer 13 is formed of a CoFe alloy, and the surface thereof is oxidized to form the specular reflection layer 16 comprising Co—Fe—O on the surface of the magnetic layer 13 . It is also preferable in the present invention to form the magnetic layers 11 and 23 with the CoFe alloy, or the magnetic layers 11 , 13 and 23 may be formed with a NiFe alloy or CoFeNi alloy or Co.

[0117] In another embodiment, the specular reflection layer 16 comprising a FeMO alloy (the element M denotes at least one of Mn, Co, Ni, Ba, Sr, Y, Gd, Cu and Zn) is deposited by sputtering on the magnetic layer 13 , or without forming the magnetic layer 13 , followed by forming the magnetic layer 23 thereon.

[0118] While it is preferable to form the pinned magnetic layer 3 having the mirror reflection layer, the mirror reflection layer may be omitted from the pinned magnetic layer 3 .

[0119] While FIG. 1 shows a laminated ferrimagnetic structure of the pinned magnetic layer 3 , this layer may be a monolayer or a multilayer of the magnetic material.

[0120] For example, the magnetic layer 11 has a thickness of about 12 to 20 Å, the intermediate layer 12 has a thickness of about 8 Å, and the magnetic layer 13 has a thickness of about 5 to 20 Å.

[0121] The intermediate layer 12 comprises a nonmagnetic conductive material such as Ru, Rh, Ir, Cr, Re or Cu.

[0122] The nonmagnetic layer 2 formed on the pinned magnetic layer 3 is formed of, for example, Cu. The layer is formed of, for example, an insulation material such as Al ₂ O ₃ when the magnetic sensing element according to the present invention is a tunnel type magnetoresistive element (AMR element) taking advantage of a principle of the tunnel effect.

[0123] A free magnetic layer 1 comprising two layers is formed on the magnetic layer 2 .

[0124] The free magnetic layer 1 comprises, for example, two layers of a NiFe alloy layer 9 and CoFe alloy layer 10 . Forming the CoFe alloy layer 10 so as to contact the nonmagnetic layer 2 as shown in FIG. 1 permits metal elements to be prevented from diffusing at the interface on the nonmagnetic layer 2 , enabling the rate of change of resistance (ΔR/R) to be increased.

[0125] The NiFe alloy layer 9 comprises, for example, 80 at % of Ni and 20 at % of Fe. The CoFe alloy layer 10 comprises, for example, 90 at % of Co and 10 at % of Fe. The NiFe alloy layer 9 has a thickness of about 45 Å, while the CoFe alloy layer 10 has a thickness of about 5 Å. Co or a CoFeNi alloy may be used in place of the CoFe alloy layer 10 . The free magnetic layer 1 may comprise a monolayer or multilayer structure of a magnetic material, and preferably comprises a monolayer structure of the CoFeNi alloy. The free magnetic layer 1 may comprise a laminated ferrimagnetic structure as in the pinned magnetic layer 3 .

[0126] A backed layer 15 comprising a metallic material or nonmagnetic metal such as Cu, Au and Ag is formed on the free magnetic layer 1 . The backed layer has a thickness of, for example, 20 Å.

[0127] A protective layer 7 is formed on the backed layer 15 . The protective layer 7 is preferably a specular reflection layer comprising an oxide such as Ta oxide.

[0128] Forming the backed layer 15 allows the so-called mean free path of the up-spin conduction electrons that contribute to the magnetoresistive effect to be expanded, and a large rate of change of resistance (ΔR/R) is obtained in the spin-valve type magnetic element by a so-called spin-filter effect, thereby enabling the magnetic element to comply with high density recording. The backed layer 15 may be omitted.

[0129] The up-spin conduction electrons performs mirror reflection at the mirror reflection layer 7 by providing the mirror reflection layer 7 on the backed layer 15 , thereby enabling the mean free path of the conduction electrons to be elongated to enable the rate of change of resistance (ΔR/R) to be further improved.

[0130] Oxides such as α-Fe ₂ O ₃ , Fe—O, Ni—O, Co—O, Co—Fe—O, Co—Fe—Ni—O, Al—O, Al—Q—O (Q denotes at least one element selected from B, Si, N, Ti, V, Cr, Mn, Fe, Co and Ni) and R—O (R denotes at least one element selected from Ti, V, Cr, Zr, Nb, Mo, Hf and W), nitrides such as Al—N, AlQ—N (Q denotes at least one element selected from B, Si, N, Ti, V, Cr, Mn, Fe, Co and Ni) and R—N (R denotes at least one element selected from Ti, V, Cr, Zr, Nb, Mo, Hf and W), and semi-metallic whistler metals such as NiMnSb and PtMnSb may be selected in addition to Ta oxide as the specular reflection layer 7 . These materials may be also used for the specular layer 16 formed on the pinned magnetic layer 3 .

[0131] The hard bias layers 5 and electrode layers 8 are formed at both sides of the laminated layers from the underlayer 6 to the protective layer (specular reflection layer) 7 . Magnetization of the free magnetic layer 1 is aligned in the track width direction (X-direction) by a vertical bias magnetic field from the hard bias layer 5 .

[0132] The hard bias layers 5 are formed of, for example, a Co—Pt (cobalt-platinum) or CoCrPt (cobalt-chromium-platinum) alloy, while the electrode layers are formed of α-Ta, Au, Cr, Cu, Rh, Ir, Ru and W. The electrode layers 8 are formed over the free magnetic layer 1 and below the antiferromagnetic layer 4 , respectively, in the tunnel type magnetoresistive element and CPP type magnetic sensing element.

[0133] A heat treatment is applied after laminating the layers from the underlayer 6 to the protective layer 7 in the spin-valve type thin film element shown in FIG. 1 , thereby generating an exchange coupling magnetic field at the interface between the antiferromagnetic layer 4 and pinned magnetic layer 3 . Magnetization of the pinned magnetic layer 3 is fixed by being oriented in a direction parallel to the Y-direction by allowing the magnetic field to be applied in the Y-direction. Since the pinned magnetic layer 3 has a laminated ferrimagnetic structure in the embodiment shown in FIG. 1 , the magnetic layers 13 and 23 are magnetized in an opposed direction to the Y-direction, when the magnetic layer 1 is magnetized, for example, in the Y-direction.

[0134] While the seed layer 22 is formed under the antiferromagnetic layer 4 in the embodiment shown in FIG. 1 , the seed layer 22 is formed of Cr in the present invention.

[0135] In addition, the seed layer comprises at least a crystalline phase, and the crystal face in at least one region of the seed layer 22 is oriented in a different direction from the direction of the crystal face in another region of the seed layer. For example, the crystal face of a crystal grain on the surface of the seed layer is oriented in a different direction from the direction of another crystal grain on the surface of the seed layer.

[0136] The seed layer 22 according to the present invention comprises Cr. Therefore, the surface energy of the surface of the seed layer is increased to put the surface in an active state as compared with the seed layer 22 comprising the NiFeCr alloy, thereby enabling the so-called wettability to be markedly improved.

[0137] Improving wettability of the surface of the seed layer 22 makes the antiferromagnetic layer 4 formed on the seed layer 22 to be ready for lamellar growth, and the crystal grain diameter in each layer formed on the seed layer to be larger than that in the related art.

[0138] Improvement of wettability as described above seems to be partly caused by different orientations among the crystal faces, or by different orientations of the crystals in different regions.

[0139] Furthermore, crystal orientation in the direction parallel to the surface of the seed layer 22 is weakened in the crystal orientation state as described above. Consequently, the atoms constituting the antiferromagnetic layer 4 are hardly affected by crystal orientation on the surface of the seed layer 22 during the film deposition process of the antiferromagnetic layer 4 on the seed layer, making the antiferromagnetic layer to be ready for uniform deposition on the seed layer 22 . In addition, wettability of seed layer 22 is quite excellent, the atoms scattered on the surface of the seed layer 22 can more freely move on the seed layer 22 , thereby allowing the atoms to be effectively and uniformly deposited on the seed layer 22 .

[0140] Since crystal orientation in the direction parallel to the direction of the surface of the seed layer 22 is weakened in the present invention as described above, it can be conjectured that no large crystal grains are found on the seed layer 22 as compared with the seed layer comprising the NiFeCr alloy.

[0141] Growth of grain boundary steps on the antiferromagnetic layer 4 deposited on the seed layer 22 is accelerated by a shadow effect caused by inclined irradiation of film deposition particles at the grain boundaries formed, when the seed layer 22 contains large crystal grains, to increase undulation on the surface of the antiferromagnetic layer 4 . However, since no large crystal grains are found in the seed layer 22 due to weak crystal grain orientation, the grain boundary steps are hardly formed at the crystal grain boundaries in the antiferromagnetic layer 4 .

[0142] Consequently, undulations are hardly generated on the surface of the antiferromagnetic layer 4 formed on the seed layer 22 , enabling lubricity of the surface of the antiferromagnetic layer 4 to be properly improved.

[0143] The seed layer 22 is formed of Cr and comprises at least a crystalline phase in the present invention. Moreover, since at least the direction of the crystal face in one region of the seed layer is different from the direction of the crystal face in another region of the seed layer, wettability of the surface of the seed layer can be markedly improved to enable lubricity of the layer on-the seed layer 22 to be improved.

[0144] The unidirectional exchange bias magnetic field (Hex*) in the pinned magnetic layer 3 may be increased in the present invention by improving wettability. The unidirectional exchange bias magnetic field (Hex*) as used herein is defined to be the magnitude of the exchange bias magnetic field (Hex*) when the rate of change of resistance (ΔR/R) decreases to half of its maximum value.

[0145] Since the pinned magnetic layer has the laminated ferrimagnetic structure, the coupling magnetic field in the RKKY mutual exchange coupling generated, for example, between the CoFe alloys constituting the pinned magnetic field 3 is included in the unidirectional exchange bias magnetic field (Hex*), in addition to the exchange coupling magnetic field generated between the pinned magnetic layer 3 and antiferromagnetic layer 4 .

[0146] The unidirectional exchange bias magnetic field (Hex*) principally means an exchange coupling magnetic field generated between the pinned magnetic field 3 and antiferromagnetic layer 4 when the pinned magnetic field 3 does not have the laminated ferrimagnetic structure. On the other hand, the unidirectional exchange bias magnetic field (Hex*) principally means a magnetic field as a combination of the exchange coupling magnetic field above and the coupling magnetic field in the RKKY mutual exchange coupling when the pinned magnetic layer 3 has the laminated ferrimagnetic structure shown in FIG. 1 .

[0147] The larger the unidirectional exchange bias magnetic field (Hex*) is, the more properly pinned the pinned magnetic layer 3 in a given direction, and magnetization of the pinned magnetic layer 3 remains to be tightly fixed in a given direction even in a high temperature environment while enabling electromigration to be suppressed, thereby enabling so-called electromigration resistance to be properly improved.

[0148] The unidirectional exchange bias magnetic field may be increased due to an increased blocking temperature as a result of increasing the crystal grain diameter in the direction parallel to the surface of each layer formed on the seed layer 22 due to quite good wettability of the surface of the seed layer 22 , or by enabling magnetic anisotropy of the crystals K _AF of the antiferromagnetic layer 4 to be large.

[0149] Since the crystal grain diameter in the direction parallel to the surface of each layer is made larger than in the related art, the same level as or larger than the rate of change of resistance (ΔR/R) in the related art may be may be obtained.

[0150] Improving lubricity of the surface of each layer formed on the seed layer 22 in the present invention permits the ferromagnetic coupling magnetic field (interlayer coupling magnetic field, H _in ) by static magnetic coupling (topological coupling) between the pinned magnetic layer 3 and free magnetic layer 1 through intervention of the nonmagnetic layer 2 to be reduced, thereby enabling asymmetry of the regenerative waveform to be reduced and regenerative characteristics to be improved. According to the experiments to be described hereinafter, the interlayer coupling magnetic field (H _in ) may come close to zero A/m.

[0151] Since lubricity of the surface of each specular reflection layers 16 or 7 itself is improved by improving lubricity of the surface of each layer on the seed layer 22 when the specular reflection layers 16 and 7 are provided as shown in FIG. 1 , specular reflectivity of each specular reflection layers 16 or 7 is improved. Therefore, the rate of change of resistance (ΔR/R) is properly improved by providing the specular reflection layer.

[0152] The thickness of seed layer 22 according to the present invention will be described hereinafter. The seed layer 22 is preferably formed with a thickness of 15 Å or more and 60 Å or less when the underlayer 6 comprising at least one element of Ta, Hf, Nb, Zr, Ti, Mo and W is formed under the seed layer 22 .

[0153] Since the seed layer cannot be densely grown with a uniform thickness when-the thickness of the seed layer 22 is smaller than 15 Å, wettability and planarity of the layer becomes insufficient while weakening the crystal orientation and reducing the mean crystal grain diameter of the antiferromagnetic layer and ferromagnetic layer formed on the seed layer 22 . Consequently, the rate of change of resistance (ΔR/R) as well as the unidirectional exchange bias magnetic field (Hex*) become small with an increased interlayer coupling magnetic field (H _in ).

[0154] A thickness of the seed layer 22 of larger than 60 Å is also not preferable, since the proportion of shunt of the sense current to the seed layer 22 increases to rapidly decrease the rate of change of resistance (ΔR/R).

[0155] A rate of change of resistance (ΔR/R) of 9% or more and a unidirectional exchange bias magnetic field (Hex*) of about 11.85×10 ⁴ A/M or more may be obtained by adjusting the thickness of the seed layer 22 within the range of 15 Å or more and 60 Å or less. A crystalline phase with a body-centered cubic structure (bcc structure) may be also properly incorporated in the seed layer 22 .

[0156] More preferably, the seed layer 22 has a thickness in the range of 20 Å or more and 60 Å or less when the underlayer 6 is provided under the seed layer 6 . Forming the seed layer 22 with a thickness of 20 Å or more allows a uniform layer to be densely grown to enable wettability to be properly improved.

[0157] The rate of change of resistance (ΔR/R) may be adjusted to 9% or more and the unidirectional exchange bias magnetic field (Hex*) may be increased to about 15.8×10 ⁴ A/m or more by forming the seed layer 22 with a thickness of 20 Å or more and 60 Å or less. The interlayer coupling magnetic field (H _in ) may also infinitely come close to zero A/m.

[0158] The thickness of the seed layer 22 is preferably in the range of 50 Å or more and 60 Å or less when the underlayer 6 is provided under the seed layer 22 .

[0159] The crystal structure of the seed layer may be completely composed of the crystalline phase by forming the seed layer 22 with a thickness of 50 Å or more. The direction of the crystal face at least in a region comprising the seed layer may be oriented in a different direction from the direction of the crystal face in another region of the seed layer. In addition, the crystal faces are rotated around a crystal axis perpendicular to the crystal face with each other, and at least a part of the equivalent crystal axes laying in the crystal face (for example the <001> axis when the crystal face is a {110} face) are oriented in different directions with each other. The crystalline phase has the body-centered cubic structure (bcc structure).

[0160] The experiment to be described hereinafter shows that the interlayer coupling magnetic field (H _in ) generated between the pinned magnetic layer 3 and free magnetic layer 1 may come close to zero A/m by forming the seed layer 22 with a thickness of 50 Å or more. Consequently, crystals may be properly oriented by forming the seed layer 22 with a thickness of 50 Å or more, thereby enabling lubricity of each layer formed on the seed layer to be properly improved.

[0161] Forming the seed layer 22 with a thickness of 50 Å or more and 60 Å or less permits the rate of change of resistance (ΔR/R) to be 9% or more and the unidirectional exchange bias magnetic field (Hex*) to be about 15.8×10 ⁴ A/m or more while enabling the interlayer coupling magnetic field (H _in ) to infinitely come close to zero A/m.

[0162] The seed layer 22 is preferably formed with a thickness of 25 Å or more and 60 Å or less, when the underlayer 6 comprising at least one element of Ta, hf, Nb, Zr, Ti, Mo and W is not formed under the seed layer 22 .

[0163] Wettability as well as planarity of the surface of the seed layer 22 becomes worse when the seed layer 22 has a thickness of 25 Å or less, because the seed layer 22 is not densely grown with a uniform thickness. Accordingly, crystal orientation of each layer of the antiferromagnetic layer and ferromagnetic layer formed on the seed layer 22 as well as the mean crystal grain diameter are reduced with decreased rate of change of resistance (ΔR/R) and unidirectional exchange bias magnetic field (Hex*), thereby increasing the interlayer coupling magnetic field (H _in ).

[0164] The seed layer 22 is formed with a thickness of 25 Å or more and 60 Å or less when underlayer 6 is provided under the seed layer 22 , which makes it possible to adjust the rate of change of resistance (ΔR/R) to 9% or more and the unidirectional exchange bias magnetic field (Hex*) to about 11.85×10 ⁴ A/m while allowing a crystalline phase to be incorporated in the layer structure. The crystalline phase has, for example, a body-centered cubic structure.

[0165] More preferably, the seed layer 22 is formed with a thickness of 30 Å or more and 60 Å or less when no underlayer 6 is provided under the seed layer 22 . Forming the seed layer 22 with a thickness of 30 Å or more allows the layer to be densely grown with uniform thickness, thereby enabling wettability to be properly improved.

[0166] Forming the seed layer with a thickness of 30 Å or more and 60 Å or less enables the rate of change of resistance (ΔR/R) to be 9% or more while increasing the unidirectional exchange bias magnetic field (Hex*) to about 15.8×10 ⁴ A/m or more. The interlayer coupling magnetic field (H _in ) may come infinitely close to zero A/m.

[0167] It is more preferable that the seed layer has a thickness of 50 Å or more and 60 Å or less when the underlayer 6 is formed under the seed layer 22 .

[0168] The seed layer 22 is completely composed of the crystalline phase by forming the seed layer 22 with a thickness of 50 Å or more. The crystal face in at least a region of the seed layer may be oriented in a different direction from the direction of the crystal face in another region of the seed layer. In addition, the crystal faces are rotated around a crystal axis perpendicular to the crystal face with each other, and at least a part of the equivalent crystal axes laying in the crystal face (for example the <001> axis when the crystal face is a {110} face) are oriented in different directions with each other. The crystalline phase has the body-centered cubic structure (bcc structure).

[0169] A rate of change of resistance (ΔR/R) of 9% or more and a unidirectional exchange bias magnetic field (Hex*) of about 15.8×10 ⁴ A/m may be obtained by forming the seed layer with a thickness of 50 Å more and 60 Å or less. The interlayer coupling magnetic field (H _in ) may also infinitely come close to zero A/m.

[0170] The underlayer itself has relatively good wettability. Therefore, the Cr atoms constituting the seed layer 22 is more uniformly deposited on the underlayer 6 to properly improve wettability of the surface of the seed layer 22 . Consequently, wettability of the seed layer 22 may be properly improved even when the seed layer 22 is as thin as, for example, about 15 Å, thereby enabling the preferable values of the unidirectional exchange bias magnetic field (Hex*) and interlayer coupling magnetic field (H _in ).

[0171] However, the effects manifested by providing the underlayer 6 cannot be obtained when no underlayer 6 is provided under the seed layer 22 . Consequently, wettability of the surface of the seed layer 22 that has been unevenly deposited becomes not so good when the seed layer 22 is too thin, thereby failing in obtaining a large unidirectional exchange bias magnetic field (Hex*). Therefore, it is effective to form a thick seed layer 22 in order to properly improve wettability of the surface of the seed layer 22 without providing the underlayer 6 . According to the experiment to be described hereinafter, forming the seed layer 22 with a thickness of 25 Å or more permits the unidirectional exchange bias magnetic field (Hex*) of about 11.85×10 ⁴ A/m or more and rate of change of resistance (ΔR/R) of 9% or more t be obtained. Consequently, the preferable thickness of the seed layer 22 is 25 Å or more when no underlayer 6 is provided under the seed layer 22 .

[0172] Not only setting of the thickness of the layer, nut also the deposition conditions for depositing the seed layer 22 is a crucial factor for obtaining the crystalline state of the seed layer 22 as described above.

[0173] It is preferable in the present invention to set the temperature of the substrate for depositing the seed layer 22 by sputtering at 20 to 100° C., the distance between the substrate and target at 40 to 80 mm, and the Ar gas pressure introduced for depositing the layer by sputtering at 0.5 to 3 mTorr (0.067 to 0.4 Pa). Controlling the deposition conditions as described above makes it possible to allow the crystalline phase to be incorporated at least in the seed layer 22 . The orientation of the crystal face in at least a region of the seed layer may be different from the orientation of the crystal face in another region of the seed layer. In other words, the orientation of the crystal face in one crystal grain on the surface of the seed layer may be different from the orientation of another crystal grain on the surface of the seed layer.

[0174] Crystal orientation of the seed layer 22 will be described in more detail hereinafter. The seed layer 22 contains at least a crystalline phase in the present invention, and the orientation of the crystal face at least in one region of the seed layer is different from the orientation of the crystal face in another region of the seed layer.

[0175] The crystal face is represented by an equivalent crystal face [110]. The equivalent crystal faces represented by [110] include (110), (1-10), (−110), (−1-10), (101), (10-1), (−101), (−10-1), (011), (01-1), (0-11) and (0-1-1) faces. These crystal faces indicate the crystal faces (real lattice face, or reciprocal lattice point in the diffraction image) in a single crystal structure represented by Miller indices. Any one of these crystal faces are represented by the [110] face.

[0176] An electron microscopic photograph to be described hereinafter indicates that the orientation of the [110] face in a region of the seed layer 22 is different from the orientation of the [110] face in another region of the seed layer.

[0177] While a total observation of the [110] face laying in the seed layer 22 indicates that the [110] face is oriented to be nearly parallel to the surface of the layer, the degree of orientation is smaller than the degree of orientation of the [111] face when the NiFeCr alloy is used for the seed layer.

[0178] It has been emphasized in the related art to enhance the degree of orientation of the [111] phase in the seed layer formed of the NiFeCr alloy. On the contrary, enhancing the degree of orientation of the [110] face is avoided in the present invention. As a result, the present invention succeeded in obtaining quite high wettability of the seed layer 22 formed of Cr while improving lubricity of each layer formed on the seed layer 22 by a synergetic effect for decreasing the degree of crystal orientation.

[0179] Diffraction spots corresponding to the reciprocal lattice points representing equivalent crystal faces are seen in the electron diffraction patterns measured in one area and another area of the seed layer. Shift of the inclined angle of each virtual line from the line normal to the layer surface obtained by connecting each diffraction spot and the origin of the beam is within an angle of zero to 45 degree, and the crystal axes laying in the crystal face, or at least a part of the equivalent crystal axes, are preferably oriented in different directions with each other.

[0180] Suppose that the crystal face is the (110) face. The diffraction spots corresponding to the reciprocal lattice points representing the (110) face in the electron beam diffraction pattern are connected to the origin of the beam. The inclination angle of the virtual line, obtained by the operation above, from the direction of the normal line to the layer surface is measured relative to the (110) faces appearing on one region and on another region of the seed layer, for example on one crystal grain and on another crystal grain on the seed layer. Then, the electron microscopic photograph shows that the (110) faces are oriented in an approximately the same direction with each other when the shift of the inclined angle of the virtual line is within an angle of zero to 45 degree. The shift of the angle of the virtual line of zero degree shows perfect alignment of the orientation of each (110) face among the crystal grains.

[0181] When the shift of the angle of the virtual line obtained from the measurement of the electron diffraction pattern of each crystal face is within a range of zero to 45 degree, the orientation of each (110) face is considered to be not so largely different, and the antiferromagnetic layer 4 may perform epitaxial growth on the crystal face. It has been conjectured that atoms tends to be in a conformity state with 1:1 correspondence with each other at the interface between the seed layer 22 and antiferromagnetic layer 4 when the antiferromagnetic layer performs epitaxial growth. However, the crystal faces are rotating with each other around the crystal axis in the direction perpendicular to the crystal face in the present invention, even when crystal faces in one region and another region of the surface of the seed layer, for example the crystal faces on one crystal grain and another crystal grain on the surface of the seed layer, are oriented approximately in the same direction. Accordingly, at leas t a part of the equivalent crystal axes (for example the <001> axis when the crystal face is {110} face) laying in the crystal face are oriented in different directions with each other.

[0182] The atoms constituting the antiferromagnetic layer 4 formed on the seed layer 22 , and the atoms constituting the seed layer 22 are liable to be not in a 1:1 correspondence state, or in a so-called non-coherent state, with each other when the crystal orientation is as described above.

[0183] Non-conformity between the seed layer 22 and antiferromagnetic layer 4 at the interface permits the antiferromagnetic layer 4 to transform from the disordered lattice (face-centered cubic lattice) to the ordered lattice (café-centered orthogonal lattice), and a large exchange coupling magnetic field may be obtained between the antiferromagnetic layer 4 and pinned magnetic layer 3 .

[0184] The mean crystal grain diameter of the crystal grains formed on each layer on the seed layer 22 in the direction parallel to the surface of the layer is preferably 200 Å or more. It is confirmed from the experiment to be described hereinafter that the mean crystal grain diameter of 200 Å or more is obtainable in the example in which the seed layer is formed of Cr.

[0185] The crystal grain diameter in the range as described above permits electromigration resistance to be improved to improve current floe reliability, while increasing the rate of change of resistance (ΔR/R) and heat resistance to the same as or larger than those in the related art.

[0186] It is preferable in the present invention that the crystal grain boundaries in the antiferromagnetic layer 4 and the crystal grain boundaries in the pinned magnetic layer 3 exposed by cutting the magnetic sensing element parallel to the direction of thickness are discontinuous with each other at least at a part of the interface between the antiferromagnetic layer 4 and pinned magnetic layer 3 .

[0187] Likewise, it is also preferable in the present invention that the crystal grain boundaries in the antiferromagnetic layer 4 and the crystal grain boundaries in the seed layer 22 exposed by cutting the magnetic sensing element parallel to the direction of thickness are discontinuous with each other at least at a part of the interface between the antiferromagnetic layer 4 and seed layer 22 .

[0188] It is preferable in the present invention that twin crystals are formed at least at a part of the antiferromagnetic layer 4 , and the interface between the twin crystals is formed at least a part of the twin crystals so as to be non-parallel to the interface at the seed layer 22 .

[0189] The so-called nonconformity is maintained at the interface between the antiferromagnetic layer 4 and pinned magnetic layer 3 , and the antiferromagnetic layer 4 properly transforms from the disordered lattice to the ordered lattice by heat treatment, thereby enabling a large exchange coupling magnetic field to be obtained, when the twin crystal is formed as described above.

[0190] For obtaining the conditions as described above, high wettability of the surface of the seed layer 22 and crystal orientation of the seed layer 22 are important in the present invention. However, it is also important to properly control the composition ratio of the antiferromagnetic layer 4 and deposition conditions of each layer formed on the seed layer 22 .

[0191] As hither to described, the composition ratio of the element X or elements X+X′ constituting the antiferromagnetic layer 4 is preferably in the range of 45 at % or more and 60 at % or less.

[0192] Among the film deposition conditions, the Ar gas pressure used for deposition by sputtering is adjusted to 3 mTorr. The heat treatment temperature for generating an exchange coupling magnetic field between the antiferromagnetic layer 4 and pinned magnetic layer 3 is adjusted to 200° C. or more and 300° C. or less, and the heat treatment is applied in a magnetic field for 2 hours or more in a vacuum of 10 ⁻⁶ Torr or less. The distance between the substrate and target is adjusted to 80 mm.

[0193] Proper nonconformity is provided at the interface between the antiferromagnetic layer 4 and pinned magnetic layer 3 , and at the interface between the antiferromagnetic layer 4 and seed layer 22 by controlling the composition ratio and deposition condition of the antiferromagnetic layer 4 , enabling an exchange coupling magnetic field of as high as about 15.8×10 ⁴ A/m or more to be obtained between the antiferromagnetic layer 4 and pinned magnetic layer 3 .

[0194] With respect to the crystal orientation of each layer formed on the seed layer 22 , the crystals of each layer on the seed layer may be predominantly oriented in the [111] direction as in the related art, or the degree of orientation in the [111] direction may be weak in the present invention.

[0195] An electron microscopic observation of the crystal orientation on the seed layer showed that the crystal orientation of the seed layer 22 (orientation of the (0-10) face) matches the crystal orientation (orientation of the (111) face) of each layer (pinned magnetic layer 3 , nonmagnetic layer 2 and free magnetic layer 1 ) above the antiferromagnetic layer 4 in the direction of thickness.

[0196] The antiferromagnetic layer 4 , pinned magnetic layer 3 , nonmagnetic layer 2 and free magnetic layer 1 seem to be deposited in accordance with the crystal orientation of the seed layer 22 . However, since atomic arrangement is in a non-coherent state at the interface between the seed layer 22 and antiferromagnetic layer 4 , and the interface between the antiferromagnetic layer 4 and pinned magnetic layer 3 , the antiferromagnetic layer 4 properly transforms from the disordered lattice to the ordered lattice by applying a heat treatment. While the crystal orientation of the antiferromagnetic layer 4 becomes to be different from the crystal orientation of the seed layer 22 due to a change of the crystal orientation of the antiferromagnetic layer 4 , the crystal orientation of each layer above the antiferromagnetic layer 4 remains unchanged by the heat treatment. Consequently, the crystal orientation of the seed layer 22 roughly matches the crystal orientation of each layer above the antiferromagnetic layer 4 in the direction of thickness.

[0197] The crystal structure of the seed layer 22 is the body-centered cubic structure (bcc structure) in the present invention. Although the face-centered cubic structure (fcc structure) has been emphasized in the related art as the crystal structure of the seed layer 22 , wettability of the surface of the seed layer 22 is quite high in the present invention even by forming the body-centered cubic structure as described above, thereby enabling the unidirectional exchange bias magnetic field (Hex*) to be improved over the related art.

[0198] The layer structure of the seed layer 22 may be also applied for other magnetic sensing elements.

[0199] FIG. 2 and the drawings thereafter denote magnetic sensing elements having different layer structures from that of the magnetic sensing element shown in FIG. 1 .

[0200] FIG. 2 is a partial cross section of the magnetic sensing element (spin-valve type thin film element) in the present invention viewed from the opposed face side to a recording medium.

[0201] In the spin-valve type thin film element shown in FIG. 2, a pair of seed layers 22 are formed on an underlayer 6 with a space corresponding to the track width Tw open in the track width direction (X-direction), and exchange bias layers 24 are formed on the seed layers 22 .

[0202] The spaces between a pair of the seed layers 22 , and between the exchange bias layers 24 are filled with an insulation layer 17 made of an insulation material such as SiO ₂ and Al ₂ O ₃ .

[0203] A free magnetic layer 1 is formed on the exchange bias layers 24 and insulation layer 17 .

[0204] The exchange bias layer 24 is formed of a X—Mn or X—Mn—X′ alloy. The composition range of the element X or elements X′ is preferably 45 at % or more and 60 at % or less, more preferably 49 at % or more and 56.5 at % or less.

[0205] Both ends of the free magnetic layer 1 are magnetized as single magnetic domains by an exchange coupling magnetic field between the exchange bias layers 24 , and magnetization of the free magnetic layer 1 in the track width region is properly aligned in the X-direction to an extent capable of responding to an external magnetic field.

[0206] As shown in FIG. 2, a nonmagnetic layer 2 is formed on the free magnetic layer 1 , and a pinned magnetic layer 3 is formed on the nonmagnetic layer 2 . An antiferromagnetic layer 4 and a protective layer 7 are additionally formed on the pinned magnetic layer 3 .

[0207] The seed layer 22 is formed of Cr in this embodiment and contains at least a crystalline phase in the seed layer 22 . The orientation of the crystal face in at least a region of the seed layer 22 is different from the orientation of the crystal face in another region of the seed layer. For example, the orientation of the crystal face of a crystal grain on the surface of the seed layer 22 is different from the orientation of the crystal face of another crystal grain on the surface of the seed layer.

[0208] The seed layer 22 is formed of Cr with the crystal orientations as described above. Consequently, wettability of the surface of the seed layer 22 may be remarkably enhanced, and the crystal grain diameter in each layer on the seed layer 22 may be increased, thereby enabling lubricity of the surface of each layer formed on the seed layer 22 to be improved while increasing the unidirectional exchange bias magnetic field (Hex*) in the free layer 1 .

[0209] According to the present invention, electromigration resistance represented by electron migration resistance may be improved while decreasing the ferromagnetic coupling magnetic field (interlayer coupling magnetic field, H _in ) by the static magnetic coupling between the free magnetic layer 1 and pinned magnetic layer 3 , thereby decreasing asymmetry of the regenerative wave form.

[0210] FIG. 1 should be cited with respect to the thickness of the seed layer 22 and other layers, since they are the same as described in FIG. 1 .

[0211] FIG. 3 is a partial cross section showing the structure of the dual spin-valve type thin film element according to the present invention.

[0212] As shown