Magneto-resistance element in which I-III-VI2 compound semiconductor is used, method for manufacturing said magneto-resistance element, and magnetic storage device and spin transistor in which said magneto-resistance element is used

Abstract

An object of the present invention is to provide a Magneto-Resistance (MR) element showing a high Magneto-Resistance (MR) ratio and having a suitable Resistance-Area (RA) for device applications. The MR element of the present invention has a laminated structure including a first ferromagnetic layer 16, a non-magnetic layer 18, and a second ferromagnetic layer 20 on a substrate 10, wherein the first ferromagnetic layer 16 includes a Heusler alloy, the second ferromagnetic layer 20 includes a Heusler alloy, the non-magnetic layer 18 includes a I-III-VI.sub.2 chalcopyrite-type compound semiconductor, and the non-magnetic layer 18 has a thickness of 0.5 to 3 nm, and wherein the MR element shows a Magneto-Resistance (MR) change of 40% or more, and has a resistance-area (RA) of 0.1 [Ωμm.sup.2] or more and 3 [Ωμm.sup.2] or less.

Claims

1. A Magneto-Resistance (MR) element having a laminated structure comprising a first ferromagnetic layer, a non-magnetic layer, and a second ferromagnetic layer on a substrate, wherein the first ferromagnetic layer comprises a Heusler alloy, the second ferromagnetic layer comprises a Heusler alloy, the non-magnetic layer comprises a I-III-VI.sub.2 chalcopyrite-type compound semiconductor, and the non-magnetic layer has a thickness of 0.5 to 3 nm, and the MR element shows a magnetoresistance (MR) change of 40% or more, and has a resistance-area (RA) of 0.1 [Ωμm.sup.2] or more and 3 [Ωμm.sup.2] or less.

2. The MR element according to claim 1, wherein the I-III-VI.sub.2 chalcopyrite-type compound semiconductor is one of the semiconductors selected from the group consisting of Cu(In.sub.1-yGa.sub.y)Se.sub.2 (0≤y≤1), Cu(In.sub.1-yGa.sub.y)S.sub.2 (0≤y≤1), Ag(In.sub.1-yGa.sub.y)Se.sub.2 (0≤y≤1), and Ag(In.sub.1-yGa.sub.y)S.sub.2 (0≤y≤1).

3. The MR element according to claim 1, wherein the Heusler alloy is a Co-based Heusler alloy selected from the group consisting of Co.sub.2MnGa.sub.xGe.sub.1-x (0≤x≤1), Co.sub.2MnGa.sub.xSn.sub.1-x (0≤x≤1), Co.sub.2MnSi.sub.xGe.sub.1-x (0≤x≤1), Co.sub.2FeGa.sub.xGe.sub.1-x (0≤x≤1), Co.sub.2Cr.sub.yFe.sub.1-yGa (0≤y≤1), Co.sub.2MnGe.sub.xSn.sub.1-x (0≤x≤1), Co.sub.2Mn.sub.yFe.sub.1-ySn (0≤y≤1), Co.sub.2-zFe.sub.zMnGe (0≤z≤2), Co.sub.2Mn.sub.yFe.sub.1-yGa (0≤y≤1), Co.sub.2Cr.sub.yFe.sub.1-ySi (0≤y≤1), Co.sub.2MnTi.sub.xSn.sub.1-x (0≤x≤1), Co.sub.2MnAl.sub.xSn.sub.1-x (0≤x≤1), Co.sub.2MnGa.sub.xSi.sub.1-x (0≤x≤1), Co.sub.2Mn.sub.yFe.sub.1-ySi (0≤y≤1), Co.sub.2MnAl.sub.xSi.sub.1-x (0≤x≤1), Co.sub.2FeGa.sub.xSi.sub.1-x (0≤x≤1), Co.sub.2FeAl.sub.xSi.sub.1-x (0≤x≤1), Co.sub.2CrAl, Co.sub.2CrGa, Co.sub.2MnSn, Co.sub.2MnAl, Co.sub.2MnGa, Co.sub.2FeSi, Co.sub.2FeAl, Co.sub.2MnGe, Co.sub.2FeGe, Co.sub.2FeGa, Co.sub.2TiSn, Co.sub.2MnSi, Fe.sub.2VAl, and Co.sub.2VAl.sub.55, the first ferromagnetic layer has B2 or L2.sub.1 structure, and the second ferromagnetic layer has B2 structure.

4. A Magneto-Resistance (MR) element having a laminated structure comprising a first ferromagnetic layer, a non-magnetic layer, and a second ferromagnetic layer on a substrate, wherein the first ferromagnetic layer comprises one or more magnetic materials selected from the group consisting of: (i) a CoCr magnetic layer having perpendicular magnetization orientation selected from the group consisting of CoCrPt, CoCrTa, CoCrTaPt, and CoCrTaNb; (ii) an RE-TM amorphous alloy magnetic layer; (iii) an artificial lattice magnetic layer selected from the group consisting of Co/Pd, Co/Pt, CoCrTa/Pd, FeCo/Pt, and FeCo/Ni; (iv) a CoPt, FePt, or FePd alloy magnetic layer; (v) a SmCo alloy magnetic layer; (vi) a soft magnetic layer selected from the group consisting of CoFe, CoNiFe, NiFe, CoZrNb, FeN, FeSi, FeAlSi, CoFeB, and FeB; and (vii) a CoCr magnetic alloy film having in-plane magnetization orientation, the second ferromagnetic layer comprises one or more magnetic materials selected from the group consisting of: (i) a CoCr magnetic layer having perpendicular magnetization orientation selected from the group consisting of CoCrPt, CoCrTa, CoCrTaPt, and CoCrTaNb; (ii) an RE-TM amorphous alloy magnetic layer; (iii) an artificial lattice magnetic layer selected from the group consisting of Co/Pd, Co/Pt, CoCrTa/Pd, FeCo/Pt, and FeCo/Ni; (iv) a CoPt, FePt, or FePd alloy magnetic layer; (v) a SmCo alloy magnetic layer; (vi) a soft magnetic layer selected from the group consisting of CoFe, CoNiFe, NiFe, CoZrNb, FeN, FeSi, FeAlSi, CoFeB, and FeB; and (vii) a CoCr magnetic alloy film having in-plane magnetization orientation, the non-magnetic layer comprises a I-III-VI.sub.2 chalcopyrite-type compound semiconductor, and the non-magnetic layer has a thickness of 0.5 to 3 nm, and the MR element shows a magnetoresistance (MR) change of 40% or more, and has a resistance-area (RA) of 0.1 [Ωμm.sup.2] or more and 3 [Ωμm.sup.2] or less.

5. A magnetic storage device using the MR element according to claim 1, wherein spin orientation in one ferromagnetic Heusler alloy layer of the MR element is fixed and spin orientation in the other ferromagnetic Heusler alloy layer is allowed to be reversible, and electric current is passed through the MR element in the lamination direction to output a value corresponding to the spin orientation in each of the layers.

6. A spin transistor using the MR element according to claim 1, wherein a gate voltage is applied to the chalcopyrite-type compound semiconductor layer, one of the ferromagnetic Heusler alloy layer of the MR element is a source layer, and the other ferromagnetic Heusler alloy layer is a drain layer.

7. A method for producing a Magneto-Resistance (MR) element comprising the steps of: forming an Ag layer on a MgO (001) single-crystal substrate and performing a heat treatment at 300° C. to 450° C. for 10 minutes to 2 hours; forming a lower Co.sub.2FeGa.sub.0.5Ge.sub.0.5 film on the Ag layer and performing heat treatment at 270° C. to 550° C. for 10 minutes to 2 hours to order the lower Co.sub.2FeGa.sub.0.5Ge.sub.0.5 into B2 or L2.sub.1 structure; forming 0.5 to 3 nm of a Cu(In.sub.0.8Ga.sub.0.2)Se.sub.2 film on the lower Co.sub.2FeGa.sub.0.5Ge.sub.0.5; and forming an upper Co.sub.2FeGa.sub.0.5Ge.sub.0.5 film on the Cu(In.sub.0.8Ga.sub.0.2)Se.sub.2 and performing heat treatment at 270° C. to 350° C. for 10 minutes to 2 hours to order the upper Co.sub.2FeGa.sub.0.5Ge.sub.0.5 wherein the MR element shows a magnetoresistance (MR) change of 40% or more, and has a resistance-area (RA) of 0.1 [Ωμm.sup.2] or more and 3 [Ωμm.sup.2] or less.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1 is a schematic diagram of layers of an MR element using CIGS according to an example of the present invention.

(2) FIG. 2 is cross-sectional images of a multilayer film using CIGS according to an example of the present invention, including (a) a HAADF-STEM image, (b) a nano-beam electron diffraction image of an upper Co.sub.2FeGa.sub.0.5Ge.sub.0.5 (hereinafter, sometimes abbreviated as CFGG), (c) a nano-beam electron diffraction image of CIGS, (d) a nano-beam electron diffraction image of a lower CFGG, and (e) a high-resolution HAADF-STEM image.

(3) FIG. 3 shows an MR curve of a CFGG/CIGS/CFGG-MR element (open circle) and a CFGG/Ag/CFGG-CPP-GMR element (open square) according to an example of the present invention at room temperature.

(4) FIG. 4 is a graph showing dependencies of MR ratio, RA, and ARA of a CFGG/CIGS/CFGG-MR element according to an example of the present invention on the inverse of a pillar area (A.sup.−1) at room temperature.

(5) FIG. 5 is a graph showing dependencies of Magneto-Resistance ratio, RA, and ARA of a CFGG/CIGS/CFGG-MR element according to an example of the present invention on the inverse of a pillar area (A.sup.−1) at low temperature.

(6) FIG. 6 is a schematic view of an example of a magnetic recording and reading device which can be equipped with a magnetic head equipped with an MR element of the present invention.

(7) FIG. 7 is a schematic view of an example of a magnetic head assembly which is equipped with an MR element of the present invention.

(8) FIG. 8 is a schematic view of an example of a magnetic head equipped with an MR element of the present invention, in which an enlarged view of a tip of a main magnetic pole and a high-frequency oscillator (a spin-torque oscillator) is provided.

(9) FIG. 9 is a family tree of an adamantine family.

(10) FIG. 10 is a schematic diagram of atomic arrangement illustrating a chalcopyrite-type crystal structure

DESCRIPTION OF EMBODIMENTS

(11) In the present embodiment, one of I-III-VI.sub.2 chalcopyrite-type compound semiconductors in the form of Cu(In.sub.1-yGa.sub.y)Se.sub.2 (wherein 0≤y≤1, preferably y=0.2, hereinafter sometimes abbreviated as CIGS) is used as a spacer material in a non-magnetic layer of an MR element having a laminated structure including a first ferromagnetic layer, a non-magnetic layer, and a second ferromagnetic layer on a substrate. For example, when y is 0.2, the above CIGS becomes Cu(In.sub.0.8Ga.sub.0.2)Se.sub.2, which is a CIGS in which some In of CuInSe.sub.2 are substituted with Ga. The Cu(In.sub.0.8Ga.sub.0.2)Se.sub.2 is known as a solar cell material and has a chalcopyrite-type crystal structure. Band gaps of CuInSe.sub.2 and CuGaSe.sub.2 are about 1.0 eV and about 1.7 eV, respectively, and vary according to amounts of substitution with Ga. A lattice constant changes from 0.56 nm to 0.58 nm by substitution with Ga. In the CIGS, y is not limited to 0.2, and may be in the range of 0≤y≤1.

(12) In the present embodiment, as a Heusler alloy used in the first and second ferromagnetic layers, when Co.sub.2FeGa.sub.xGe.sub.1-x (0≤x≤1) in which x is 0.5 is adopted, the Heusler alloys become Co.sub.2Fe(Ga.sub.0.5Ge.sub.0.5) (hereinafter, sometimes referred as CFGG). A lattice constant of the Heusler alloy is 0.573 nm, resulting in particularly good lattice matching to Cu(In.sub.0.8Ga.sub.0.2)Se.sub.2. There has been no report to date on MTJ or CPP-GMR in which Cu(In.sub.0.8Ga.sub.0.2)Se.sub.2 is used as a spacer.

EXAMPLES

(13) Results of Experiments

(14) FIG. 1 shows a structure of layers of an MR element produced. The structure of layers is MgO (001) substrate/Cr (10 nm)/Ag (100 nm)/CFGG (10 nm)/CIGS (2 nm)/CFGG (10 nm)/Ru (8 nm). All layers were formed at room temperature.

(15) In steps for production, the MgO (001) single-crystal substrate was subjected to heat flushing in a sputter chamber before layer formation at 550° C. for 1 hour. After the Ag layer was formed, surface flatness of the Ag was improved by heat treatment at 300° C. After the lower CFGG layer was formed, heat treatment was performed at 500° C. to order the lower CFGG into L2.sub.1 structure. After all the layers were formed, heat treatment was performed at 300° C. for ordering the upper CFGG.

(16) Structure of a multilayer film was analyzed using a transmission electron microscope (TEM). Transport properties were analyzed by a four probe method. An MR element was prepared by micromachining using an electron-beam lithography, Ar ion milling, and lift off. A pillar prepared was elliptical. Some pillars having sizes of 200*100 nm.sup.2 to 400*200 nm.sup.2 were provided.

(17) FIG. 2 shows HAADF-STEM images and nano-beam electron diffraction images of the multilayer film produced. A layered structure is clearly observed in the HAADF-STEM image in FIG. 2(a). It is recognized from the nano-beam electron diffraction images of FIG. 2(b) to FIG. 2(d) that the upper CFGG has B2 structure, the lower CFGG has L2.sub.1 structure, and the CIGS has chalcopyrite structure. These layers have grown epitaxially and have an orientation relationship of (001)[110].sub.cFGG//(001)[110].sub.CIGS. A high-resolution HAADF-STEM image is shown in FIG. 2 (e). Periodic changes in contrast corresponding to the B2 and L2.sub.1 structures of the upper and lower CFGG layers are observed. Misfit dislocation is not observed in the CFGG/CIGS interface, which shows that lattice matching is remarkably good.

(18) FIG. 3 shows a representative MR curve. Open circles indicate MRs of the CIGS spacer (2 nm) and open squares indicate those of an Ag spacer (5 nm). The Ag spacer is shown as a reference. An element including the Ag spacer shows an MR ratio of 20%. On the other hand, an element including the CIGS spacer shows a significantly high MR ratio of 40%.

(19) FIG. 4 shows a graph of MR ratio, RA, and ARA versus the inverse of a pillar area (A.sup.−1). The measurement was conducted at room temperature. Although RA varies from 0.1 to 3 [Ωμm.sup.2], MR ratio is about 40%. Although the reason for the variation of RA is not clear, it can be found that preferred RA for application to a reading element of HDD and MRAM was obtained.

(20) FIG. 5 shows temperature dependencies of Magneto-Resistance ratio, RA, and ΔRA. MR ratios exceed 100% at 8K. There were about 10 to 20% increases in RA at low temperature, which shows that the increases in MR ratios at low temperature were due to increases in ΔRA. The decreases in RA with falling temperature represent that an electron transport mechanism of the CIGS spacer is a tunneling type. Thus, it is thought that the electron transport mechanism is different from that of the CPP-GMR element.

(21) FIG. 6 is a schematic oblique view of the principal part illustrating a simplified construction of a magnetic recording and reading device which can be equipped with a magnetic head equipped with an MR element of the present invention. In FIG. 6, a magnetic recording and reading device 100 is a device having a structure using a rotary actuator. In the Figure, a recording media disk 110 rotates in the direction of the arrow A by a motor (not shown) which is mounted on a spindle 140 and responds to a control signal from a motor control unit (not shown). The magnetic recording and reading device 100 may have two or more media disks 110.

(22) A schematic view illustrating an example of a magnetic head assembly equipped with an MR element of the present invention is provided by FIG. 7.

(23) FIG. 7 is an enlarged oblique view of a part of the magnetic head assembly between an actuator arm 154 and the end, which is viewed from the disk side. That is, a magnetic head assembly 150 has the actuator arm 154 having, for example, a bobbin portion supporting a drive coil or the like, and one end of the actuator arm 154 is connected with a suspension 152.

(24) A head slider 120 which records and reads data stored in a media disk 110 shown in FIG. 6 is mounted on the end of a suspension 152 which has a form of thin plate as shown in FIG. 7. Herein, the head slider 120 is equipped with, for example, a magnetic head equipped with an MR element of the present invention in the vicinity of the end of the head slider 120.

(25) When the media disk 110 rotates, the Air Bearing Surface (ABS) of the head slider 120 is maintained above the surface of the media disk 110 with a predetermined flying height. Alternatively, the slider may be a so-called “contact-type” in which the slider comes in contact with the media disk 110.

(26) The suspension 152 is connected to one end of an actuator arm 154 having, for example, a bobbin portion (not shown) which supports a drive coil. The other end of the actuator arm 154 is equipped with a voice coil motor 130 which is a type of linear motor. The voice coil motor 130 includes a drive coil (not shown) wound around a bobbin portion of the actuator arm 154 and a magnetic circuit (not shown) composed of a permanent magnet and an opposed yoke which are placed so as to sandwich the coil and face each other.

(27) The actuator arm 154 is supported with ball bearings (not shown) placed on the spindle 140, and can freely rotate and slide by the voice coil motor 130.

(28) The suspension 152 includes a lead wire 158 for writing and reading a signal. The lead wire 158 and each electrode of a magnetic head mounted on the head slider 120 are electrically connected. The reference sign 156 in the figure represents an electrode pad of the magnetic head assembly 150.

(29) FIG. 8 is a schematic oblique view illustrating a main magnetic pole and a high-frequency oscillator (a spin-torque oscillator). As shown in FIG. 8, a spin-torque oscillator 180 is placed between a tip 162 of a main magnetic pole 160 and a leading end surface 174 of an auxiliary magnetic pole 170. The spin-torque oscillator 180 includes a primary layer 182 composed of a non-magnetic conductive layer, a spin injection layer (first magnetic layer) 184, an intermediate layer 186 (a non-magnetic layer), an oscillation layer (second magnetic layer) 188, and a capping layer 190 composed of a non-magnetic conductive layer, which are stacked from the main magnetic pole 160 toward the auxiliary magnetic pole 170 in the order. The oscillation layer 188 is composed of soft magnetic FeCoNi having a high saturation flux density of 2 T. The intermediate layer 186 is composed of Cu having a long spin diffusion length, and the spin injection layer 184 is composed of an artificial lattice of Co/Ni having a high coercive force and a high spin polarization. Although FIG. 8 illustrates an example stacked in the order of a spin injection layer 184, an intermediate layer 186, and an oscillation layer 188, the order of stacking may be an oscillation layer, an intermediate layer, and a spin injection layer.

(30) In the intermediate layer 186, a material having a high spin transmission, such as Au or Ag may be used. The intermediate layer 186 preferably has a layer thickness of that of monoatomic layer to 3 nm. This enables control of a switched connection between the spin injection layer 184 and the oscillation layer 188 to give an optimal value.

(31) In the spin injection layer 184, materials having a superior perpendicular orientation, for example, CoCr magnetic layers having a magnetization orientation perpendicular to the layers, such as CoCrPt, CoCrTa, CoCrTaPt, and CoCrTaNb; RE-TM amorphous alloy magnetic layers such as TbFeCo; artificial lattice magnetic layers such as Co/Pd, Co/Pt, CoCrTa/Pd, FeCo/Pt, and FeCo/Ni; alloy magnetic layers such as CoPt and FePt; SmCo alloy magnetic layers; soft magnetic layers having a relatively high saturation flux density and magnetic anisotropy in the in-plane direction of the layer, such as CoFe, CoNiFe, NiFe, CoZrNb, FeN, FeSi, and FeAlSi; Heusler alloys selected from the group consisting of CoFeSi, CoMnSi, and CoMnAl, and the like; and CoCr magnetic alloy films having in-plane magnetization orientation can be suitably used. In addition, two or more of the above materials may be stacked and the resulting laminated material may be used.

(32) In the oscillation layer 188, a laminated material of Fe, Co, Ni, an alloy of these elements, or an artificial lattice including a combination thereof, and various materials which can be used in the above spin injection layer 184 may be used. In addition, in the oscillation layer 188, a FeCo alloy to which at least one of Al, Si, Ge, Ga, Mn, Cr, and B is added may be used. This enables control of, for example, saturation flux densities, anisotropic magnetic fields, and spin torque transmission efficiencies of the oscillation layer 188 and the spin injection layer 184.

(33) The layer thickness of the oscillation layer 188 is preferably 5 to 20 nm, and the layer thickness of the spin injection layer 184 is preferably 2 to 60 nm.

(34) A bottom surface 192 of the spin-torque oscillator 180 is exposed at a disk-facing surface (not shown), and mounted at about the same height of the tip surface of the main magnetic pole 160 above the surface of a magnetic disk (not shown). That is, the bottom surface 192 of the spin-torque oscillator 180 is flush with the disk-facing surface of a slider, and approximately parallel to the surface of the magnetic disk. The spin-torque oscillator 180 is the most distant from the disk-facing surface, and has a top surface 194 extending approximately parallel to the bottom surface 192 and two lateral surfaces 196 and 198 extending from the lower end surface to the upper end surface.

(35) At least one lateral surface, for example two lateral surfaces 196 and 198 in this figure, inclines from vertical direction to the disk-facing surface toward the center of tracks, that is, inclines inward. The surface of the spin-torque oscillator 180 facing the main magnetic pole 160 is a symmetrical trapezoid which is parallel to the width direction of the tracks.

(36) In the spin-torque oscillator 180, when a voltage is applied between the main magnetic pole 160 and the auxiliary magnetic pole 170 from a power supply (not shown) according to a control signal by a control circuit board, a direct current is passed through the spin-torque oscillator 180 in the film thickness direction. The current can rotate magnetization of the oscillation layer 188 of the spin-torque oscillator 180, leading to generation of a high-frequency magnetic field. Accordingly, the spin-torque oscillator 180 applies the high-frequency magnetic field to a recording layer of a magnetic disk. Thus, the auxiliary magnetic pole 170 and the main magnetic pole 160 act as electrodes which apply current vertically to the spin-torque oscillator 180.

(37) Although the above examples show a magnetic tunnel junction element having a laminated structure including a first ferromagnetic layer, a non-magnetic layer, and a second ferromagnetic layer on a substrate, in which Cu(In.sub.0.8Ga.sub.0.2)Se.sub.2 is used in the non-magnetic layer and Co.sub.2Fe(Ga.sub.0.5Ge.sub.0.5) is used in the first and second ferromagnetic layers, the present invention is not limited thereto. Of course, other I-III-VI.sub.2 chalcopyrite-type compound semiconductors may be used in the non-magnetic layer, and other Heusler alloys and other ferromagnetic materials may be used in the first and second ferromagnetic layers.

INDUSTRIAL APPLICABILITY

(38) The present invention provides an MR element showing a significant MR change and having a resistance-area of about 0.1 to 3 Ωμm.sup.2. Thus, the MR element can be applied to a magnetoresistive random-access memory (MRAM), a reading head of a hard disk drive (HDD), and a spin logic element.

REFERENCE SIGNS LIST

(39) 100 MAGNETIC RECORDING AND READING DEVICE 110 RECORDING MEDIA DISK 120 HEAD SLIDER 130 VOICE COIL MOTOR 140 SPINDLE 150 MAGNETIC HEAD ASSEMBLY 160 MAIN MAGNETIC POLE 170 AUXILIARY MAGNETIC POLE 180 SPIN-TORQUE OSCILLATOR