DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0065] FIG. 1 is a partial sectional view, as viewed from the side of a sensor surface positioned to face a recording medium, of a magnetoresistive sensor according to a first embodiment of the present invention.

[0066] A magnetoresistive sensor shown in FIG. 1 is a GMR head for reproducing an external signal recorded on a recording medium. Though not shown, an inductive head for recording may be formed so as to overlie the magnetoresistive sensor. Note that, in FIG. 1 , the sensor surface positioned to face the recording medium is a plane parallel to the X-Z plane. Also, when the magnetoresistive sensor is used in a floating magnetic head, the sensor surface positioned to face the recording medium means the so-called ABS (Air Bearing Surface).

[0067] The magnetoresistive sensor is formed on a trailing end surface of a slider made of, e.g., alumina-titanium-carbide (Al ₂ O ₃ —TiC). The slider is joined to an elastically deformable support member made of a stainless material, for example, on the side of a surface opposed to the sensor surface positioned to face the recording medium, whereby a magnetic head device is constituted.

[0068] The term “direction of the track width” means the direction of width of an area in which the direction of magnetization varies with an external magnetic field. By way of example, the direction of the track width is the direction of magnetization resulting when no external magnetic field is applied to the free magnetic layer, i.e., the X-direction as shown.

[0069] Furthermore, a recording medium is positioned opposite to a surface of the magnetoresistive sensor positioned to face the recording medium, and is in the Z-direction as shown. The direction of a magnetic field leaked from the recording medium is the Y-direction as shown.

[0070] Reference numeral 20 shown in FIG. 1 denotes a lower shielding layer formed of a magnetic material such as a NiFe alloy. In this embodiment, the lower shielding layer 20 serves also as a lower electrode.

[0071] A first hard magnetic layer 21 formed of a hard magnetic material is formed on the lower shielding layer 20 , a nonmagnetic layer 22 is formed on the first hard magnetic layer 21 , and a second hard magnetic layer 23 is formed on the nonmagnetic layer 22 . In this embodiment, those three layers, i.e., the first hard magnetic layer 21 , the nonmagnetic layer 22 , and the second hard magnetic layer 23 , constitute a pinned magnetic layer 24 .

[0072] As shown in FIG. 1, a nonmagnetic material layer 25 is formed on the pinned magnetic layer 24 . The nonmagnetic material layer 25 is formed of an electrically conductive material having a low electrical resistance, such as Cu.

[0073] Then, a free magnetic layer 26 is formed on the nonmagnetic material layer 25 . A nonmagnetic layer 27 is formed on the free magnetic layer 26 , and a support ferromagnetic layer 28 is formed on the nonmagnetic layer 27 . Further, an antiferromagnetic layer (referred to also as a second antiferromagnetic layer in the following description) 30 is formed on the support ferromagnetic layer 28 .

[0074] In the embodiment shown in FIG. 1, a laminate from the pinned magnetic layer 24 to the antiferromagnetic layer 30 is referred to as a multilayered film 31 . As shown in FIG. 1 , the multilayered film 31 has opposite end surfaces 31 a , 31 a spaced in the direction of the track width (X-direction as shown), which are formed by etching opposite end portions of the multilayered film 31 from a top surface toward a bottom surface. The etched surfaces are formed until reaching an intermediate depth point of the second hard magnetic layer 23 . A track width Tw is defined by a width size of the free magnetic layer 26 between the opposite end surfaces 31 a and 31 a spaced in the direction of the track width.

[0075] Also, in the embodiment shown in FIG. 1 , opposite end portions of the films positioned from midway the second hard magnetic layer 23 to the first hard magnetic layer 21 on the lower side are not subjected to the above-mentioned etching, and those films have a greater width size in the direction of the track width than the track width Tw.

[0076] In the embodiment shown in FIG. 1 , insulating layers 32 are formed so as to cover upper surfaces 23 a of the second hard magnetic layer 23 , which are extended outward from an area corresponding to the track width Tw, and the opposite end surfaces 31 a of the multilayered film 31 . The insulating layers 32 are each formed of a known insulating material such as Al ₂ O ₃ and SiO ₂ .

[0077] In the embodiment shown in FIG. 1 , an upper shielding layer 33 made of a magnetic material, such as a NiFe alloy, is formed to cover a top surface 31 b of the multilayered film 31 and upper surfaces 32 a of the insulating layers 32 . The upper shielding layer 33 serves also as an upper electrode of the magnetoresistive sensor.

[0078] In the embodiment shown in FIG. 1 , because the lower shielding layer 20 and the upper shielding layer 33 each function not only as a shielding, but also as an electrode, a gap length G1 is decided based on the film thickness from the first hard magnetic layer 21 to the antiferromagnetic layer 30 , and hence a value of the gap length G1 can be reduced.

[0079] In the embodiment shown in FIG. 1 , the shielding layers 20 , 33 serving also as electrodes are formed respectively on the lower and upper sides of the multilayered film 31 made up of from the first hard magnetic layer 21 to the antiferromagnetic layer 30 , thereby constituting a CPP (Current Perpendicular to the Plane) type structure in which a current flows between the shielding layer 20 and 33 in the direction of thickness of the multilayered film 31 (Z-direction as shown).

[0080] In the magnetoresistive sensor of this embodiment, when the magnetic field leaked from the recording medium is applied in the Y-direction, the magnetization of the free magnetic layer 26 is changed from a direction parallel to the X-direction toward the Y-direction. Depending on the relationship between a variation in the direction of magnetization of the free magnetic layer 26 and the fixed direction of magnetization of the second hard magnetic layer 23 in the pinned magnetic layer 24 , electrical resistance is changed (this is called the magnetoresistive effect). As a result, the magnetic field leaked from the recording medium is detected in accordance with a voltage change caused upon the change in value of the electrical resistance.

[0081] Features of the magnetoresistive sensor shown in FIG. 1 will be described below.

[0082] In the embodiment shown in FIG. 1 , the pinned magnetic layer 24 is formed in a three-layered structure comprising the first hard magnetic layer 21 , the second hard magnetic layer 23 , and the nonmagnetic layer 22 interposed between these two layers.

[0083] In the related art, the pinned magnetic layer ( 4 in FIGS. 13 and 14 ) is formed as a ferromagnetic layer of, e.g., a NiFe alloy or a CoFe alloy. Then, an antiferromagnetic layer is formed in contact with an interface of the pinned magnetic layer in the direction of film thickness (Z-direction as shown) to generate an exchange coupling magnetic field between the pinned magnetic layer and the antiferromagnetic layer by performing heat treatment under a magnetic field, whereupon the magnetization of the pinned magnetic layer is pinned in the height direction (Y-direction as shown).

[0084] By contrast, in the embodiment of FIG. 1 , the above antiferromagnetic layer in the related art is not employed and the hard magnetic layers 21 , 23 are used to constitute the pinned magnetic layer 24 . The magnetization of the pinned magnetic layer 24 is pinned by utilizing strong coercive forces Hc of the hard magnetic layers 21 , 23 .

[0085] More specifically, in the embodiment shown in FIG. 1 , each of the first hard magnetic layer 21 and the second hard magnetic layer 23 constituting the pinned magnetic layer 24 has a stronger coercive force Hc than that of a NiFe alloy, a CoFe alloy, etc. When a magnetic field is applied to the pinned magnetic layer 24 in the height direction (Y-direction as shown), by way of example, without heat treatment, the second hard magnetic layer 23 is magnetized in the same direction as that of the applied magnetic field, i.e., the height direction, and the magnetization of the second hard magnetic layer 23 is pinned in the height direction by its own coercive force Hc. On the other hand, the magnetization of the first hard magnetic layer 21 is reversed by exchange coupling with respect to the second hard magnetic layer 23 based on the RKKY interaction through the nonmagnetic layer 22 . Thus, the magnetization of the first hard magnetic layer 21 is oriented in a direction opposed to the height direction (i.e., direction opposed to the Y-direction as shown) in which the second hard magnetic layer 23 is magnetized, and then pinned in the direction opposed to the height direction by its own coercive force Hc and the exchange coupling based on the RKKY interaction.

[0086] By providing hard magnetic regions, which are formed as the hard magnetic layers, in the pinned magnetic layer 24 as in the embodiment shown in FIG. 1 , the following advantages are expected.

[0087] First, the pinned magnetic layer 24 can be formed in a larger film thickness t2. The first hard magnetic layer 21 and the second hard magnetic layer 23 constituting the pinned magnetic layer 24 have a film thickness t4 and t3, respectively. When the magnetization of the pinned magnetic layer ( 4 in FIGS. 13 and 14 ) is pinned by the exchange coupling magnetic field generated between the pinned magnetic layer and the antiferromagnetic layer like the related art, there has been a problem that the exchange coupling magnetic field is reduced as the film thickness of the pinned magnetic layer increases. On the other hand, when the magnetization of the pinned magnetic layer 24 is pinned by utilizing the strong coercive forces Hc of the first hard magnetic layer 21 and the second hard magnetic layer 23 themselves like the embodiment shown in FIG. 1 , the pinned magnetization can be maintained by the strong coercive forces Hc even with an increase of the film thicknesses t3, t4 of the hard magnetic layers 21 , 23 , and the hard magnetic layers 21 , 23 can be formed in larger film thicknesses t3, t4. In the CPP type magnetoresistive sensor shown in FIG. 1 , therefore, it is possible to increase the film thickness t2 of the pinned magnetic layer 24 and hence to increase the product (ΔRA) of a resistance change amount (ΔR) and a sensor area (A) in the direction parallel to the film surfaces.

[0088] In the embodiment shown in FIG. 1 , the second hard magnetic layer 23 is a layer actually contributing to the magnetoresistive effect. Accordingly, by setting the film thickness t3 of the second hard magnetic layer 23 to be larger than the film thickness t4 of the first hard magnetic layer 21 , a greater effect of bulk scattering is expected and a further increase of ΔRA can be achieved. With the increase of ΔRA, a higher reproduction output can be obtained.

[0089] A second advantage resulting from the feature that the magnetization of the pinned magnetic layer 24 is pinned by utilizing the strong coercive forces Hc of the first hard magnetic layer 21 and the second hard magnetic layer 23 themselves without utilizing the exchange coupling magnetic field generated at the interface between the pinned magnetic layer 24 and the antiferromagnetic layer, as shown in FIG. 1 , resides in point of enabling the magnetization of the pinned magnetic layer 24 and the magnetization of the free magnetic layer 26 to easily and reliably cross each other in an orthogonal state.

[0090] When employing the antiferromagnetic layers 5 , 11 to pin the magnetization of the pinned magnetic layer 4 and the magnetization in the opposite end portions of the free magnetic layer 2 like the related art shown in FIG. 14 , the heat treatment under the magnetic field must be performed twice. In such a case, there are several restrictions regarding conditions, such as the intensity of the magnetic field and the temperature of the heat treatment. Unless the proper heat treatment under the magnetic field is performed within those restrictions, a satisfactory orthogonal relation cannot be achieved between the magnetization of the pinned magnetic layer 4 and the magnetization of the free magnetic layer 2 .

[0091] On the other hand, in the embodiment shown in FIG. 1 , the magnetization of the pinned magnetic layer 24 is pinned without utilizing the exchange coupling magnetic field generated at the interface between the pinned magnetic layer and the antiferromagnetic layer, and the pinned magnetic layer 24 is made up of the first hard magnetic layer 21 and the second hard magnetic layer 23 each having a strong coercive force Hc. Therefore, magnetization control of the hard magnetic layers 21 , 23 can be performed by applying a magnetic field without heat treatment. Under the effect of the magnetic field applied for the magnetization control of the hard magnetic layers 21 , 23 , the magnetizations of the free magnetic layer 26 and the support ferromagnetic layer 28 are temporarily oriented in the same direction as that of the applied magnetic field. However, because, as described later, interlayer coupling acts between the free magnetic layer 26 and the support ferromagnetic layer 28 and an exchange coupling magnetic field acts between the support ferromagnetic layer 28 and the antiferromagnetic layer 30 , the magnetizations of the free magnetic layer 26 and the support ferromagnetic layer 28 are returned again to the direction of the track width (X-direction as shown) upon release of the applied magnetic field. Consequently, the magnetization of the free magnetic layer 26 and the magnetization of the pinned magnetic layer 24 are properly held in an orthogonal state.

[0092] In the embodiment shown in FIG. 1 , there are no restrictions imposed on the intensity of the magnetic field to be applied for pinning the magnetizations of the hard magnetic layers 21 , 23 . For example, the applied magnetic field may be set greater than the interlayer coupling acting between the free magnetic layer 26 and the support ferromagnetic layer 28 and the exchange coupling magnetic field generated between the support ferromagnetic layer 28 and the antiferromagnetic layer 30 . The reason resides in that no heat treatment is performed when applying the magnetic field to pin the magnetizations of the hard magnetic layers 21 , 23 . Because of no heat treatment being performed, the magnetizations of the support ferromagnetic layer 28 and the free magnetic layer 26 are returned again to a direction parallel to the direction of the track width (X-direction as shown) upon release of the applied magnetic field under the actions of the exchange coupling magnetic field and the interlayer coupling mentioned above, whereby the magnetization of the pinned magnetic layer 24 and the magnetization of the free magnetic layer 26 can be held in a satisfactory orthogonal state.

[0093] Thus, in the embodiment shown in FIG. 1 , since delicate restrictions, which have been required in the related art, are no longer required for achieving the orthogonal state of the magnetizations of the pinned magnetic layer 24 and the free magnetic layer 26 , the magnetizations of the pinned magnetic layer 24 and the free magnetic layer 26 can be easily and reliably made cross each other in an orthogonal state.

[0094] As characteristics required for the first hard magnetic layer 21 and the second hard magnetic layer 23 , each of the first hard magnetic layer 21 and the second hard magnetic layer 23 must have a strong coercive force Hc. This is because the magnetizations of the first hard magnetic layer 21 and the second hard magnetic layer 23 cannot be effectively pinned in a direction parallel to the height direction unless each layer has the strong coercive force Hc. The strong coercive force Hc of each of the first hard magnetic layer 21 and the second hard magnetic layer 23 is preferably not less than about 15.8×10 ³ (A/m) [=200 Oe].

[0095] A description is now made of characteristics required for the first hard magnetic layer 21 and the second hard magnetic layer 23 from the viewpoint of, in particular, increasing ΔRA.

[0096] To increase ΔRA, each of the first hard magnetic layer 21 and the second hard magnetic layer 23 preferably has a higher β value and a higher specific resistance value ρ. ΔRA is expressed by the following formula (1):

ΔRA∝[β ² /(1−β ² )]·ρ· t

[0097] As seen from the formula (1), for the purpose of increasing ΔRA, it is preferable that the β value be higher, the specific resistance value ρ be higher, and the film thickness t be larger. As described above, because the hard magnetic layers 21 , 23 each have the strong coercive force Hc, the hard magnetic layers 21 , 23 can be formed in larger film thicknesses t3, t4 and the film thicknesses t3, t4 of the hard magnetic layers 21 , 23 can be increased to increase ΔRA. However, those film thicknesses are preferably smaller than the spin diffusion distance of a conductive spin within the ferromagnetic layer. Here, the term “spin diffusion distance” represents how far a conductive spin diffuses (moves) while holding an up-spin or a down-spin. If those film thicknesses are larger than the spin diffusion distance, this increases the probability that an up-spin electron having entered the ferromagnetic layer is changed to a down-spin electron somewhere within the ferromagnetic layer. On the other hand, the magnetoresistive effect can be enhanced with an increase of the mean free path of an up-spin and a decrease of the mean free path of a down-spin. When the up-spin is changed to the down-spin, the mean free path of the up-spin is interrupted at that point. For that reason, those film thicknesses are preferably set smaller than the spin diffusion distance.

[0098] Next, the β value is a value specific to the material properties of the hard magnetic layers 21 , 23 and satisfies a formula (2), i.e., ρ⇓/ρ↑=(1+β)/(1−β) [where ρ⇓ represents a specific resistance value with respect to down-spin ones of conductive electrons, and ρ↑ represents a specific resistance value with respect to up-spin ones of conductive electrons].

[0099] The reason (mechanism) why the resistance change amount (ΔR) is increased with an increase of the β value is as follows. With an increase of the β value, as seen from the above formula (2), the specific resistance value (ρ⇓) with respect to the down-spin conductive electrons is increased, and the specific resistance value (ρ↑) with respect to the up-spin conductive electrons is decreased. This can be interpreted as implying that the down-spin conductive electrons become harder to flow in the hard magnetic layer or are shut out and the mean free path of the down-spin conductive electrons is shortened (which results in an insulating behavior), while the up-spin conductive electrons become easier to flow in the hard magnetic layer and the mean free path of the up-spin conductive electrons is lengthened (which results in a metallic behavior), whereby the difference in mean free path between the up-spin conductive electrons and the down-spin conductive electrons is increased (which results in an increase of bulk scattering).

[0100] Each of the first hard magnetic layer 21 and the second hard magnetic layer 23 preferably has the β value of 0.3 or more in absolute value. Note that the β value is defined to be within the range of larger than −1, but smaller than 1. Accordingly, a preferable β value is not smaller than 0.3, but smaller than 1 in absolute value.

[0101] Next, the specific resistance value ρ represents a mean value of specific resistance values with respect to the down-spin and up-spin conductive electrons. The specific resistance value ρ of each of the hard magnetic layers 21 , 23 is preferably not smaller than 30 (μΩ·cm).

[0102] Further, a saturation magnetization Ms of each of the hard magnetic layers 21 , 23 is preferably not larger than 1.4 T. The saturation magnetization Ms preferably has a smaller value for the reason that, because this condition is effective to reduce a demagnetizing field which is in proportion to Ms×t (magnetic moment per unit area, t=film thickness) and affects the direction of magnetization of the free magnetic layer 26 , the film thicknesses t3, t4 of the hard magnetic layers 21 , 23 can be increased and hence ΔRA can be increased.

[0103] A description is now made of a hard magnetic material having the above-mentioned properties, i.e., a strong coercive force Hc, a high β value, and a high specific resistance value ρ.

[0104] The first hard magnetic layer 21 and the second hard magnetic layer 23 are each preferably formed of a CoPt alloy, a CoPtX alloy (where X represents one or more noble metal elements selected from among Ru, Re, Pd. Os, Ir, Pt, Au and Rh), or a CoPtY alloy (where Y represents one or more elements selected from among Sc, Ti, V, Cr, Mn, Fe, Co, Ni and Cu).

[0105] The above-mentioned materials are all hard magnetic materials and are each able to have a coercive force Hc of not less than 15.8×10 ³ (A/m) [=200 Oe]. Also, those materials can be set to a β value of not smaller than 0.3 in absolute value and a specific resistance value ρ of not smaller than 30 (μΩ·cm).

[0106] Incidentally, the CoPtX alloy is an alloy obtained by adding a noble metal element X to CoPt, and the CoPtY alloy is an alloy obtained by adding a 3d-block transition element Y to CoPt.

[0107] According to experiment results described later, the Pt amount of the CoPt alloy, the CoPtX alloy or the CoPtY alloy is preferably not less than 12 at %, but not more than 34 at %. This range of Pt amount ensures that the coercive force Hc can be set not less than 15.8×10 ³ (A/m) [=200 Oe] and the specific resistance value ρ can be set not smaller than 30 (μΩ·cm). Also, the saturation magnetization Ms can be set not more than 1.4 T. The crystal structure of the CoPt alloy, etc. is in a mixed state of a crystal phase close to pure Co and a crystal phase close to pure Pt. Many of Co and Pt are not brought into a solid solution state.

[0108] The Pt amount is more preferably not less than 15 at %, but not more than 30 at %, even more preferably not less than 17 at %, but not more than 29 at %, and most preferably not less than 18 at %, but not more than 26 at %. According to experiment results described later, it is possible to further increase the coercive force Hc, further increase the specific resistance value, and further reduce the saturation magnetization by narrowing the Pt composition ratio toward the above-mentioned optimum range.

[0109] In particular, by setting the Pt amount to be not less than 18 at %, but not more than 26 at %, the coercive force Hc can be increased to 63.2×10 ³ (A/m) [=800 oe] or more and the specific resistance value ρ can be increased to the range of 37 to 42 (μΩ·cm). Also, the saturation magnetization Ms can be reduced down to 1.2 T or less.

[0110] In each of the composition ratio ranges mentioned above, the Pt amount is more preferably not less than 26 at %. By setting the Pt amount to be not less than 26 at %, the coercive force Hc can take a high value in the range of 15.8×10 ³ [=200 Oe] to 63.2×10 ³ (A/m) [=800 Oe], and the magnetizations of the first hard magnetic layer 21 and the second hard magnetic layer 23 can be pinned with stability. Also, a specific resistance value of not smaller than about 42 (μΩ·cm) can be obtained and therefore ΔR can be increased. Further, since the saturation magnetization Ms can be held down to about 1.2 T or less, the film thicknesses of the first hard magnetic layer 21 and the second hard magnetic layer 23 can be increased and hence ΔR can be increased while weakening the effect of demagnetizing fields upon the free magnetic layer 26 .

[0111] Additionally, in the embodiment shown in FIG. 1 , because of a structure in which the first hard magnetic layer 21 and the second hard magnetic layer 23 are stacked with the nonmagnetic layer 22 interposed therebetween, the overall coercive force Hc of the pinned magnetic layer 24 can be increased in comparison with the case of constituting the pinned magnetic layer 24 as a single hard magnetic layer, for example. As a result, the magnetization of the pinned magnetic layer 24 can be more effectively pinned.

[0112] FIG. 8 is a conceptual view of a hysteresis loop resulting when the pinned magnetic layer 24 is made up of the two hard magnetic layers 21 , 23 with the nonmagnetic layer 22 interposed therebetween, as shown in FIG. 1 . It is assumed, for example, that the magnetic moment (saturation magnetization Ms×film thickness t) per unit area of the first hard magnetic layer 21 (direction of magnetization thereof is denoted by P 1 in FIG. 8 ) is smaller than the magnetic moment per unit area of the second hard magnetic layer 23 (direction of magnetization thereof is denoted by P 2 in FIG. 8 ). It is also assumed that the external magnetic field is applied to the right as viewed in FIG. 8 .

[0113] When the magnitude of the magnetic field applied for control in pinning the magnetization of the pinned magnetic layer 24 exceeds the coercive force Hc, the magnetizations of the first and second hard magnetic layers 21 , 23 are brought into an antiparallel state. When the magnitude of the magnetic field applied to the right as viewed in FIG. 8 is increased, the resultant magnetic moment per unit area of the pinned magnetic layer 24 is also increased at a certain gradient. With a further increase in the magnitude of the magnetic field applied to the right as viewed in FIG. 8 , the magnetizations of the first hard magnetic layer 21 and the second hard magnetic layer 23 are brought into a perfectly parallel state in which they are both oriented to the right as viewed in FIG. 8 and the resultant magnetic moment per unit area has a constant value.

[0114] The coercive force Hc of the pinned magnetic layer 24 made up of the two hard magnetic layers 21 , 23 with the nonmagnetic layer 22 interposed therebetween is given by a coercive Hca shown in FIG. 8 . When the pinned magnetic layer 24 is constituted, for example, as a single hard magnetic layer, the coercive force Hc of the pinned magnetic layer 24 is given by a coercive force Hcb in FIG. 8 , which is smaller than the coercive force Hca obtained with the pinned magnetic layer 24 made up of the two hard magnetic layers 21 , 23 with the nonmagnetic layer 22 interposed therebetween.

[0115] Thus, to increase the coercive force Hc of the pinned magnetic layer 24 , the pinned magnetic layer 24 is preferably of a multilayered structure made up of the two hard magnetic layers 21 , 23 with the nonmagnetic layer 22 interposed therebetween. With such a multilayered structure, the pinned magnetization of the pinned magnetic layer 24 becomes harder to reverse under the effect of the external magnetic field, and reproduction characteristics can be effectively improved.

[0116] A description is now made of the film thicknesses t3, t4 of the first hard magnetic layer 21 and the second hard magnetic layer 23 . In this embodiment, the film thicknesses t3, t4 of the first hard magnetic layer 21 and the second hard magnetic layer 23 are each preferably not less than 30 Å, but not more than 200 Å. The reason why the film thicknesses t3, t4 are each set not less than 30 Å resides in that, when forming the pinned magnetic layer using a ferromagnetic material such as a NiFe alloy in the past, the pinned magnetic layer has been formed in a film thickness of not more than 30 Å.

[0117] Also, the film thickness t2 of the pinned magnetic layer 24 is preferably not less than 70 Å, but not more than 400 Å.

[0118] Further, the product of the coercive force Hc and the film thickness t for each of the first hard magnetic layer 21 and the second hard magnetic layer 23 is required to be different between the two layers. For example, when both the first hard magnetic layer 21 and the second hard magnetic layer 23 are made of the same material and have the same coercive force Hc, the two layers are preferably formed in different film thicknesses t3, t4 from each other. If the first hard magnetic layer 21 and the second hard magnetic layer 23 are formed to have the same coercive force Hc and the film thicknesses t3, t4 equal to each other, the magnetizations of the first hard magnetic layer 21 and the second hard magnetic layer 23 cannot be brought into a satisfactory antiparallel state when a magnetic field is applied to bring the magnetizations of the first hard magnetic layer 21 and the second hard magnetic layer 23 into an antiparallel state.

[0119] In addition, as described above, the film thickness t3 of the second hard magnetic layer 23 is preferably set larger than the film thickness t4 of the first hard magnetic layer 21 for the purpose of effectively causing bulk scattering. However, if the difference in film thickness between those two layers is too large, this would be not preferable.

[0120] The reason resides in that a larger difference in film thickness increases the demagnetizing fields generated from the opposite end portions of the pinned hard magnetic layer 24 in the direction of the track width (X-direction as shown). In the multilayered structure made up of the two hard magnetic layers 21 , 23 with the nonmagnetic layer 22 interposed therebetween as shown in FIG. 1 , however, the demagnetizing fields can be effectively weakened by properly adjusting the film thicknesses of the hard magnetic layers 21 , 23 in comparison with the case of forming the pinned magnetic layer 24 of only one hard magnetic layer. This is because, when the hard magnetic layers 21 , 23 are formed of the same material in different film thicknesses t3, t4 from each other, for example, the demagnetizing fields are generated just in amount corresponding to the difference in film thickness. It is therefore important to properly adjust the difference in film thickness for the purpose of weakening the demagnetizing fields. In the embodiment shown in FIG. 1 , the difference between the film thickness t4 of the first hard magnetic layer 21 and the film thickness t3 of the second hard magnetic layer 23 is preferably not less than 10 Å, but not more than 100 Å.

[0121] While the nonmagnetic layer 22 is interposed between the first hard magnetic layer 21 and the second hard magnetic layer 23 , the nonmagnetic layer 22 is preferably formed of one or an alloy of two or more selected from among Ru, Rh, Ir, Cr, Re and Cu. By forming the nonmagnetic layer 22 of a predetermined element, such as Ru, it is possible to develop exchange coupling between the first hard magnetic layer 21 and the second hard magnetic layer 23 based on the RKKY interaction, and to properly bring the magnetizations of the first hard magnetic layer 21 and the second hard magnetic layer 23 into an antiparallel state.

[0122] Also, the nonmagnetic layer 22 is preferably formed in a film thickness of not less than 3 Å, but not more than 15 Å. By properly adjusting the film thickness of the nonmagnetic layer 22 within the above-mentioned range, it is possible to enhance the exchange coupling between the first hard magnetic layer 21 and the second hard magnetic layer 23 based on the RKKY interaction, and to properly bring the magnetizations of the first hard magnetic layer 21 and the second hard magnetic layer 23 into an antiparallel state.

[0123] The magnitude of the exchange coupling based on the RKKY interaction must be greater than the coercive force Hc of each of the first hard magnetic layer 21 and the second hard magnetic layer 23 . The reason resides in that, if the coercive force Hc of at least one of the first hard magnetic layer 21 and the second hard magnetic layer 23 is greater than the exchange coupling based on the RKKY interaction, the magnetizations of the first hard magnetic layer 21 and the second hard magnetic layer 23 could not be properly brought into an antiparallel state in a direction parallel to the height direction (Y-direction as shown), and a deterioration of reproduction characteristics would result in. For example, by forming the nonmagnetic layer 22 of Ru and setting the film thickness of the nonmagnetic layer 22 to be not less than 8 Å, but not more than 11 Å, the magnitude of the exchange coupling based on the RKKY interaction can be increased up to about 39.5×10 ³ (A/m).

[0124] In the embodiment shown in FIG. 1 , the pinned magnetic layer 24 is formed on the side lower than the free magnetic layer 26 as viewed in the drawing, and opposite end portions of the second hard magnetic layer 23 , which constitutes the pinned magnetic layer 24 , spaced in the direction of the track width (X-direction as shown) are etched away until reaching an intermediate depth point of the second hard magnetic layer 23 , as indicated by the opposite end surfaces 31 a , so that the width size of the pinned magnetic layer 24 , left on the lower side than the etched portions, in the direction of the track width (X-direction) is extended to be greater than the track width Tw. This structure contributes to further weakening the effect, upon the free magnetic layer 26 , of the demagnetizing fields generated in the opposite end portions of the pinned hard magnetic layer 24 spaced in the direction of the track width (X-direction as shown), and therefore to more effectively improving the reproduction characteristics. In other words, as seen from FIG. 1 , since the opposite end portions of the pinned magnetic layer 24 extended over regions beyond the track width Tw are positioned more distant from the free magnetic layer 26 , it is possible to further weaken the effect, upon the free magnetic layer 26 , of the demagnetizing fields generated from those regions of the pinned magnetic layer 24 extended beyond the track width Tw.

[0125] Stated otherwise, as shown in FIG. 1 , the opposite end portions of the second hard magnetic layer 23 constituting the pinned magnetic layer 24 require to be etched away until reaching an intermediate depth point of the second hard magnetic layer 23 so that a central portion of the second hard magnetic layer 23 has a reduced width size comparable to the track width Tw. The reason resides in that the second hard magnetic layer 23 of the pinned magnetic layer 24 is a layer directly contributing to the magnetoresistive effect. By reducing the width size of the second hard magnetic layer 23 in the direction of the track width to a value approximately equal to the track width Tw at least until reaching an intermediate depth point of the second hard magnetic layer 23 , the reproduction output can be satisfactorily increased. Also, by etching away the opposite end portions of the second hard magnetic layer 23 at least until reaching an intermediate depth point thereof, as indicated by the opposite end surfaces 31 a , so that the second hard magnetic layer 23 left under the etched portions has a larger width size in the direction of the track width than the track width Tw, it is possible to properly generate the exchange coupling between the first hard magnetic layer 21 and the second hard magnetic layer 23 based on the RKKY interaction, and to properly bring the magnetizations of the first hard magnetic layer 21 and the second hard magnetic layer 23 into an antiparallel state.

[0126] The nonmagnetic material layer 25 is formed of a nonmagnetic electrically conductive material such as Cu, and it is preferably formed in a larger film thickness than the nonmagnetic material layer used in the related art. While in the related art the nonmagnetic material layer (corresponding to 25 ) has been formed in a film thickness of about 20 Å, the nonmagnetic material layer 25 in the embodiment of FIG. 1 is formed in a larger film thickness of about 50 Å to 100 Å. The reason resides in that, if the film thickness of the nonmagnetic material layer 25 is so thin as in the related art, the coercive force Hc of, in particular, the second hard magnetic layer 23 constituting the pinned magnetic layer 24 , which is positioned closer to the free magnetic layer 26 , is transferred to the free magnetic layer 26 and therefore the sensitivity of the free magnetic layer 26 to the external magnetic field is reduced. Further, when the magnetoresistive sensor is of CPP type like the embodiment shown in FIG. 1 , there occurs no problem of reducing the product (ΔRA) of a resistance change amount (ΔR) and a sensor area (A) even if the film thickness of the nonmagnetic material layer 25 is set larger than that of the nonmagnetic material layer used in the magnetoresistive sensor of CIP type (in which a sensing current is supplied to flow in a direction parallel to the film surfaces of the multilayered film 31 ). In the embodiment shown in FIG. 1 , therefore, the nonmagnetic material layer 25 is formed in a relatively large film thickness of not less than about 50 Å, but not more than about 100 Å.

[0127] A description is now made of materials of the free magnetic layer 26 , a manner of controlling the magnetization, and so on. In the embodiment shown in FIG. 1 , the free magnetic layer 26 is of a single-layer structure made of a magnetic material. The free magnetic layer 26 is preferably formed of NiFe or NiFeX (where X represents one or more elements selected from among Al, Si, Ti, V, Cr, Mn, Cu, Zr, Nb, Mo, Ru, Rh, Hf, Ta, W, Ir and Pt). The reason resides in that, if the free magnetic layer 26 is formed as a single-layer structure of CoFe, reproduction sensitivity would be low, hysteresis would deteriorate, and reproduction characteristics would be inferior to the case of forming the free magnetic layer 26 of NiFe or NiFeX.

[0128] The free magnetic layer 26 is formed in a film thickness of, e.g., 100 Å. Additionally, the film thickness of the free magnetic layer 26 is preferably not less than 40 Å, but not more than 150 Å.

[0129] Above the free magnetic layer 26 , as shown in FIG. 1 , the support ferromagnetic layer 28 and the antiferromagnetic layer 30 are successively formed in this order with the nonmagnetic layer 27 interposed therebetween.

[0130] The nonmagnetic layer 27 is formed of one or an alloy of two or more selected from among Ru, Rh, Ir, Cr, Re and Cu. In this embodiment the nonmagnetic layer 27 is formed in a film thickness of, e.g., 8 Å.

[0131] The support ferromagnetic layer 28 is formed of, e.g., NiFe, NiFeX (where X represents one or more elements selected from among Al, Si, Ti, V, Cr, Mn, Cu, Zr, Nb, Mo, Ru, Rh, Hf, Ta, W, Ir and Pt), CoFe, or CoFeCr. To increase an exchange coupling magnetic field generated between the support ferromagnetic layer 28 and the antiferromagnetic layer 30 , the support ferromagnetic layer 28 of a single-layer structure is preferably formed of a ferromagnetic material containing Co. Also, the support ferromagnetic layer 28 is preferably formed in a film thickness of more than 0 Å, but not more than 30 Å.

[0132] The antiferromagnetic layer 30 is preferably formed of a PtMn alloy, an X—Mn alloy (where X represents one or more elements selected from among Pd, Ir, Rh, Ru and Os), or a Pt—Mn—X′ alloy (where X′ represents one or more elements selected from among Pd, Ir, Rh, Ru, Au, Ag, Os, Cr, Ni, Ar, Ne, Xe and Kr).

[0133] By using one of the above-mentioned alloys as the antiferromagnetic layer 30 and heat-treating it, an exchange coupling film comprising the support ferromagnetic layer 28 and the antiferromagnetic layer 30 and generating a large exchange coupling magnetic field can be obtained.

[0134] In the magnetoresistive sensor shown in FIG. 1 , the direction of magnetization of the support ferromagnetic layer 28 is oriented and pinned in a direction crossing the direction of magnetization of the pinned magnetic layer 24 (i.e., the height direction) by the exchange coupling magnetic field generated between the support ferromagnetic layer 28 and the antiferromagnetic layer 30 .

[0135] Further, because the free magnetic layer 26 is opposed to the support ferromagnetic layer 28 with the nonmagnetic layer 27 interposed therebetween, the free magnetic layer 26 is brought into a single domain state by the interlayer coupling magnetic field, i.e., the RKKY interaction in this case, through the support ferromagnetic layer 28 and the nonmagnetic layer 27 , and the direction of magnetization of the free magnetic layer 26 is oriented in a direction crossing the direction of magnetization of the pinned magnetic layer 24 . The magnetizations of the free magnetic layer 26 and the support ferromagnetic layer 28 are oriented in the same direction as that of the track width (X-direction as shown). Incidentally, the film thickness of the nonmagnetic layer 27 is preferably not less than 3 Å, but not more than 15 Å.

[0136] Thus, since the transition to the single domain state and the direction of magnetization of the free magnetic layer 26 are controlled by the interlayer coupling magnetic field generated between the free magnetic layer 26 and the support ferromagnetic layer 28 through the nonmagnetic layer 27 , it is possible to suppress disturbance of the longitudinal bias magnetic field applied to the free magnetic layer 26 and hence disturbance of the domain structure of the free magnetic layer 26 , which are otherwise caused by the external magnetic field such as the magnetic field leaked from the recording medium.

[0137] When the nonmagnetic layer 27 is made of Ru and an artificial ferri-state is established in which the directions of magnetizations of the free magnetic layer 26 and the support ferromagnetic layer 28 are made 180° different from each other, the film thickness of Ru is preferably in the range of 8 Å to 11 Å or in the range of 15 Å to 21 Å.

[0138] In the present invention, the exchange coupling magnetic field generated between the antiferromagnetic layer 30 and the support ferromagnetic layer 28 is increased to firmly pin the direction of magnetization of the support ferromagnetic layer 28 in a direction crossing the direction of magnetization of the pinned magnetic layer 24 . In addition, by setting the magnitude of the interlayer coupling magnetic field generated between the free magnetic layer 26 and the support ferromagnetic layer 28 to be smaller than the exchange coupling magnetic field generated between the antiferromagnetic layer 30 and the support ferromagnetic layer 28 , the free magnetic layer 26 is brought into a single domain state and the direction of magnetization of the free magnetic layer 26 is surely oriented in a direction orthogonal to the direction of magnetization of the pinned magnetic layer 24 while allowing the direction of magnetization of the free magnetic layer 26 to fluctuate with the leakage magnetic field.

[0139] To increase the exchange coupling magnetic field generated between the antiferromagnetic layer 30 and the support ferromagnetic layer 28 and to set the magnitude of the interlayer coupling magnetic field generated between the free magnetic layer 26 and the support ferromagnetic layer 28 to be smaller than the above exchange coupling magnetic field, the magnitude of magnetic moment (Ms×t; product of density of saturation magnetic flux and film thickness) per unit area of the support ferromagnetic layer 28 is set smaller than the magnitude of magnetic moment (Ms×t; product of density of saturation magnetic flux and film thickness) per unit area of the free magnetic layer 26 in this embodiment. More practically, a ratio of the magnitude of magnetic moment (Ms×t) per unit area of the free magnetic layer 26 to the magnitude of magnetic moment (Ms×t) per unit area of the support ferromagnetic layer 28 (i.e., Ms×t of the free magnetic layer 26 /Ms×t of the support ferromagnetic layer 28 ) is preferably set to be in the range of not less than 3, but not more than 20.

[0140] In the magnetoresistive sensor shown in FIG. 1 , control of the transition to the single domain state and the direction of magnetization of the free magnetic layer 26 can be adjusted in two stages, i.e., with the magnitude of the exchange coupling magnetic field generated between the antiferromagnetic layer 30 and the support ferromagnetic layer 28 and the magnitude of the interlayer coupling magnetic field generated between the support ferromagnetic layer 28 and the free magnetic layer 26 , whereby fine control can be easily achieved.

[0141] Accordingly, it is possible to properly and easily control the transition to the single domain state and the direction of magnetization of the free magnetic layer 26 , and to promote further narrowing of the track width in the magnetoresistive sensor.

[0142] Moreover, by employing the multilayered structure of the free magnetic layer 26 /the nonmagnetic layer 27 /the support ferromagnetic layer 28 /the antiferromagnetic layer 30 as described above, the free magnetic layer 26 can be formed in a larger film thickness up to about 100 Å. As a result, the product (ΔRA) of the resistance change amount (ΔR) and the sensor area (A) can be further increased, and hence a further increase of the reproduction output can be achieved.

[0143] FIG. 2 is a partial sectional view, as viewed from the side of a sensor surface positioned to face a recording medium, of a magnetoresistive sensor according to a second embodiment of the present invention.

[0144] Of layers shown in FIG. 2 , ones denoted by the same reference numerals as those in FIG. 1 represent the same layers as those in FIG. 1 .

[0145] In the embodiment shown in FIG. 2 , the layers constituting the multilayered film 31 shown in FIG. 1 are formed in a reversed order. More specifically, a multilayered film 31 of this embodiment is constituted by successively forming, on a lower shielding layer 20 , an antiferromagnetic layer 30 , a support ferromagnetic layer 28 , a nonmagnetic layer 27 , a free magnetic layer 26 , a nonmagnetic material layer 25 , a second hard magnetic layer 23 , a nonmagnetic layer 22 , and a first hard magnetic layer 21 in this order from the lowermost side.

[0146] In the embodiment shown in FIG. 2 , the multilayered film 31 has opposite end surfaces 31 a , 31 a spaced in the direction of the track width (X-direction as shown), which are formed by etching opposite end portions of the multilayered film 31 from a top surface 31 b downward until reaching an intermediate depth point of the free magnetic layer 26 . A track width Tw is defined by a width size of the partly etched free magnetic layer 26 between the opposite end surfaces 31 a and 31 a spaced in the direction of the track width.

[0147] The reason why, in FIG. 2 , opposite end portions of the free magnetic layer 26 are cut halfway by etching, as indicated by the opposite end surfaces 31 a , while the opposite end portions of the free magnetic layer 26 on the lower side are not subjected to the etching and are formed to extend beyond the track width Tw, resides in properly generating interlayer coupling between the free magnetic layer 26 and the support ferromagnetic layer 28 and properly bringing the magnetization of the free magnetic layer 26 into a single domain state in the direction of the track width (X-direction as shown).

[0148] In the embodiment shown in FIG. 2 , as in FIG. 1 , the pinned magnetic layer 24 is formed in a three-layered structure comprising the first hard magnetic layer 21 , the second hard magnetic layer 23 , and the nonmagnetic layer 22 interposed between these two layers. Because the first hard magnetic layer 21 and the second hard magnetic layer 23 each have a strong coercive force Hc, the magnetizations of the layers 21 , 23 are pinned by their own coercive forces Hc in a direction parallel to the height direction without utilizing the exchange coupling magnetic field generated at the interface between the pinned magnetic layer and the antiferromagnetic layer. In the embodiment shown in FIG. 2 , the magnetizations of the first hard magnetic layer 21 and the second hard magnetic layer 23 are brought into an antiparallel state by exchange coupling generated between the first hard magnetic layer 21 and the second hard magnetic layer 23 based on the RKKY interaction.

[0149] With the structure of pinning the magnetizations of the first hard magnetic layer 21 and the second hard magnetic layer 23 by their own strong coercive forces Hc like the embodiment shown in FIG. 2 , the magnetizations of the first hard magnetic layer 21 and the second hard magnetic layer 23 can be maintained in a pinned state by the strong coercive forces Hc even when their film thicknesses are increased, and therefore the first hard magnetic layer 21 and the second hard magnetic layer 23 can be formed in larger film thicknesses than those in the related art. Further, in the CPP-type magnetoresistive sensor shown in FIG. 2 , since the film thickness of the pinned magnetic layer 24 can be increased, the product (ΔRA) of the resistance change amount (ΔR) and the sensor area (A) in a plane parallel to the film surfaces can be increased and hence a further increase of the reproduction output is expected.

[0150] Also, in the embodiment shown in FIG. 2 , since the pinned magnetic layer 24 is made up of the first hard magnetic layer 21 and the second hard magnetic layer 23 each having a strong coercive force Hc without utilizing the exchange coupling magnetic field generated at the interface between the pinned magnetic layer and the antiferromagnetic layer for control of the magnetization of the pinned magnetic layer 24 , the magnetizations of the hard magnetic layers 21 , 23 can be controlled by applying a magnetic field without heat treatment. Under the effect of the magnetic field applied for the magnetization control of the hard magnetic layers 21 , 23 , the magnetization of the free magnetic layer 26 is temporarily oriented in the same direction as that of the applied magnetic field. However, because, as described later, an appropriate level of interlayer coupling acts between the free magnetic layer 26 and the support ferromagnetic layer 28 , the magnetization of the free magnetic layer 26 is returned again to the direction of the track width (X-direction as shown) upon release of the applied magnetic field. Consequently, the magnetization of the free magnetic layer 26 and the magnetization of the pinned magnetic layer 24 are properly held in an orthogonal state.

[0151] In the embodiment shown in FIG. 2 , therefore, the magnetizations of the pinned magnetic layer 24 and the free magnetic layer 26 can be more easily and reliably can be made orthogonal to each other in comparison with the related art.

[0152] In the embodiment shown in FIG. 2 , it is thought that demagnetizing fields generated from ends of the pinned magnetic layer 24 are increased in comparison with those in the embodiment shown in FIG. 1 . The reason resides in that, as shown in FIG. 2 , the first hard magnetic layer 21 and the second hard magnetic layer 23 constituting the pinned magnetic layer 24 have the opposite end surfaces 31 a spaced in the direction of the track width (X-direction as shown), which are entirely given as continuous surfaces formed by etching. However, because FIG. 2 employs the multilayered structure made up of the two hard magnetic layers 21 , 23 with the nonmagnetic layer 22 interposed therebetween, the demagnetizing fields affecting the direction of magnetization of the free magnetic layer can be weakened in comparison with the case of constituting the pinned magnetic layer 24 as a single hard magnetic layer alone.

[0153] FIG. 3 is a partial sectional view, as viewed from the side of a sensor surface positioned to face a recording medium, of a magnetoresistive sensor according to a third embodiment of the