JP2000294854A - Magnetoresistive element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To significantly exceed the rates of change of reluctance observed in reproducing elements such as MR heads by providing magnetic particles with rutile-type crystal structure in a granular tunnel magnetoresistive material of such a structure that the magnetic particles are dispersed in insulator phase. SOLUTION: An Au electrode 2 is formed on a quartz substrate 1 by sputtering and an oxide film 3 of Ti and Cr, 1 μm in film thickness, is formed thereon by oxygen reactive sputtering in Ar+O2 gas using a Ti-Cr-O target. Thereafter, CrO2 particles are deposited in the oxide film 3 by heat treatment to form a granular film 3' with TiO2 of rutile-type crystal structure in insulation phase. A Au electrode film 4 is formed thereon by sputtering to obtain a magnetoresistive element. The magnetoresistive element uses a novel granular tunnel magnetoresistive material and a rate of change of reluctance not less than 9% is obtained at room temperature.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a magnetoresistive element used for a magnetic field sensor, and more particularly to a magnetoresistive element of a magnetoresistive head (MR head, GMR head) used as a reproducing head in magnetic recording. is there.

[0002]

2. Description of the Related Art In recent years, the progress of magnetic recording has been remarkable, and the recording density has been improved to reduce the size and weight in the field of home VTR and to reduce the size and capacity in the field of magnetic disk drives. ing.

In particular, taking a magnetic disk device as an example, the development of a recording / reproducing separation type head for improving the recording density is active. An MR head is used as a reproducing head of the recording / reproducing separation type head. Hereinafter, a reproducing head using a multilayer film having a magnetic film exhibiting a magnetoresistive effect is abbreviated as an MR head. When the relative speed between the medium and the head is reduced due to the miniaturization of the magnetic disk drive, the output of the conventional inductive head is reduced, but the output of the MR head is constant regardless of the relative speed. This is because it has the feature of being. This M
A single layer film of a permalloy film is usually used for the magnetic sensing portion of the R head.

On the other hand, the fact that a magnetoresistive element in which a few atomic layers of a nonmagnetic layer are sandwiched between ferromagnetic layers having different anisotropic magnetic fields exhibits a large magnetoresistance effect is based on a spin valve made of cobalt / Cu / iron nickel. Type of reproducing element.

Next, the basic principle of the conventional granular tunnel magnetoresistance effect will be described. An insulator film containing ferromagnetic metal fine particles (for example, cobalt ₅₂ Al ₂₀ O
₂₈ ) shows a magnetoresistance, according to a report by Fujimori et al. (H. Fujimori, S. Mita Nickel and S. Ohnuma: Mat. Sc.
i. Eng. B31 (1995) p219.). This is generally understood as follows. The electric conduction in such a composite system is caused by the tunnel effect between the magnetic particles of the upward spin electrons and the downward spin electrons, and the density of states of the electrons at the Fermi level in the metal particles contributing to the conduction depends on the spin. . Therefore, the tunnel conductance differs between a case where the magnetizations of the two magnetic particles are parallel and a case where the magnetizations are antiparallel. Therefore, the tunnel current when the direction of magnetization of each magnetic particle is aligned by the magnetic field is different from the tunnel current in the absence of a magnetic field, giving a magnetoresistance effect. This is generally called a granular tunnel magnetoresistance effect.

[0006]

The permalloy film of the MR head has good sensitivity due to a small anisotropic magnetic field, but the magnetoresistance effect is at most 3%, which is not so large. for that reason,
An MR head using a permalloy single-layer film for the magnetic sensing portion has a disadvantage that the reproduction output is not always sufficient.

[0007] The magnetoresistive change rate of the spin-valve type reproducing element is less than 10%, and a higher magnetoresistive change rate is desired as a next-generation reproducing element for high recording density. Further, in a multilayer film in which a magnetic layer and a non-magnetic layer are combined and laminated, the number of layers to be laminated increases as the improvement of the magnetoresistance ratio is improved. However, in the MR head, there is a tendency that the size of the reproducing gap for arranging the MR element is reduced in order to cope with high-density recording, and it is required to reduce the number of stacked layers and to reduce the thickness of the reproducing element. It is an object of the present invention to propose a novel granular tunnel magnetoresistive material and to provide a magnetoresistive element that greatly exceeds the magnetoresistance change rate found in a reproducing element such as the MR head.

[0008]

The magnetoresistive element of the present invention is a granular type tunnel magnetoresistive material having a structure in which magnetic particles are dispersed in an insulator phase, wherein the magnetic particles have a rutile type crystal structure. It is desirable to use a chromium oxide having a rutile crystal structure as the magnetic particles. In addition, in the insulator phase, it is desirable that the magnetic particles are dispersed so as not to be in direct contact with each other, but a unit in which several magnetic particles are assembled is dispersed as a whole. Even with a structure, the function of the present invention can be achieved. Note that a large magnetoresistance change rate can be obtained by filling the insulating phase with magnetic particles as densely as possible while satisfying the above-mentioned particle dispersion state.

In the present invention, the insulator phase has a rutile-type crystal structure, a titanium oxide, and a halide of M (M = magnesium, nickel, cobalt, iron, zinc,
Manganese), or one or more of aluminum oxide and silicon oxide. As the halide of M, it is preferable to use a fluoride of M, for example, one having a chemical formula of MF ₂ as a main component.
Examples of the titanium oxide include those having a chemical formula of TiO ₂ as a main component. When magnetic particles are incorporated as fine particles into such an insulator phase, the magnetic particles are microcrystalline particles having a particle diameter smaller than that of a single magnetic domain, and are dispersed so that their easy axes of magnetization are random. Is preferred. Here, the single magnetic domain particle size is a particle size of a particle having a single magnetic domain in a magnetic particle, or a particle of a particle in a substantially single magnetic domain state in which one main magnetic domain and other minute magnetic domains do not move. Refers to the diameter.
Further, in the present invention, the size of the magnetic particles is 0.5 to 5 nm, and the thickness of the insulating phase between the magnetic particles is 0.5 to 5 nm.
It is preferably 3 nm.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The idea according to the present invention has been derived from consideration of the generation mechanism of the granular tunnel magnetoresistance effect described below. In the granular type magnetic particles, tunneling conduction is caused by electrons near the Fermi level of the majority spin and the minority spin. However, when the magnetization of the two magnetic particles is parallel or antiparallel, either The electronic density of states of the majority and minority spins of the magnetic particles is reversed. Therefore, when electrons cross two magnetic particles during conduction, the number of states near the Fermi level that electrons of each spin can take in each magnetic particle differs between the case where the magnetization is parallel and the case where the magnetization is antiparallel. It is considered that there is a difference in electric resistance between the two.

Therefore, if the electronic state density near the Fermi level in the magnetic particle is extremely different between the majority spin and the minority spin, that is, one state density has a finite value near the Fermi level, When the density of states of the other spin is 0 near the Fermi level, when the magnetizations of the two magnetic particles are parallel, the electron of the spin having a finite value near the Fermi level can tunnel, In the case of antiparallel, a spin having a finite state density in one magnetic particle has a state density of 0 in the other magnetic particle. Therefore, tunnel electrons of any spin do not flow, and the electric resistance may be significantly increased. Be expected.

A metal oxide having a rutile-type crystal structure is expected to be a substance that satisfies such conditions of the electronic state. Figure 3 shows SFMater et al. (J. de Physique France
2,315 (1992)) is an electron density of states of CrO ₂ calculated by. In FIG. 3, the upper half represents the density of states of majority (up) spin, and the lower half represents the density of states of minority (down) spin. In addition, the horizontal axis is the energy measured from the Fermi energy E _F. The state density of majority spins has a finite value near the Fermi level, but the state density of minority spins has a gap of about 3 eV near the Fermi level and the state density is zero.

That is, in such a substance, it is considered that electrons of majority spin show metallic behavior, while electrons of minority spin show insulator or semiconductor behavior. Therefore, when such a material is incorporated as fine particles in an insulator, it is expected that tunnel conduction is possible when the magnetizations are parallel, and a complete insulator is obtained when the magnetizations are antiparallel. Chromium oxide having a rutile-type crystal structure has an easy axis of magnetization along the c-axis and has an anisotropic magnetic field of 1 kOe or less at room temperature.

Therefore, when microcrystalline grains of chromium oxide having a single magnetic domain grain size or less are dispersed in the insulator so that the axis of easy magnetization is random, the case where the magnetization becomes parallel depending on the magnitude of the external magnetic field is realized. Is done. In other words, this granular insulating film is expected to have a remarkable change in magnetoresistance depending on the magnitude and direction of the external magnetic field.

The present inventor made a composite film of chromium oxide as the magnetic particles and titanium oxide having the same rutile type crystal structure as the insulator based on the above idea, and measured the magnetoresistance effect. It was confirmed that the magnetoresistance change rate of was obtained. In the magnetoresistive material of the present invention, as the insulating phase, rutile-type titanium oxide, a halide of M (M = magnesium, cobalt, nickel,
Zinc) or one or more of silicon oxide and aluminum oxide can be used. This is because these elements do not substitute for chromium oxide and are excellent in magnetically shielding.

The size of the magnetic particles is 0.5 to 5 nm, and the thickness of the insulating phase between the magnetic particles is 0.5 to 3 nm. If the thickness of the ferromagnetic layer is less than 0.5 nm, the influence of the grain interface on the electric resistance is too weak, and if it exceeds 5 nm, the total surface area is reduced and the tunnel magnetoresistance effect is weakened. If the thickness of the insulating phase between the magnetic particles is less than 0.5 nm, the magnetic insulation of the magnetic particles is weak, and if it exceeds 3 nm, the resistance itself increases and the effect of the magnetoresistance is weakened.

[0017]

The present invention will be described below with reference to examples. (Embodiment 1) FIG. 1 shows a process for forming a reproducing element of this embodiment. First, an Au electrode 2 is formed on a quartz substrate 1 by a sputtering method, and a 1 μm-thick Ti and Cr oxide film 3 is formed on the Au electrode 2 by an oxygen reaction sputtering using an Ar + O ₂ gas using a Ti—Cr—O target. Filmed (step 1). Then, CrO ₂ is introduced into the oxide film 3 by heat treatment.
The particles were deposited to form a granular film 3 'using TiO ₂ as an insulating phase (Step 2). An Au electrode film 4 was formed thereon by sputtering. Granular film 3 'and Au
The bonding area of the electrode 4 was 1 mm × 1 mm (Step 3). Through the above steps, a sample of the reproducing element was manufactured.

A magnetic field of 4 [KA / m] was applied to the sample, and the magnetoresistance ratio was measured by a DC four-terminal method. As a result, even in the case of a substantially composite single layer film, a magnetoresistance change rate of 11% was obtained at room temperature, and a magnetoresistance change rate of about 3% using a conventional material such as permalloy for the magnetic layer. A magnetoresistance change rate several times larger than that of the laminated film having the above was confirmed.

Example 2 Samples were prepared using targets of various compositions in the same manner as in Example 1, and their magnetoresistance ratios were measured. In each case, the thickness of the granular film was 1 μm, the applied magnetic field was 4 [KA / m], and the measurement temperature was 21.
° C. The results are summarized in FIG. According to the configuration of this example, a magnetoresistance ratio (magnetic susceptibility) of 9% or more could be obtained even when the composition of the insulating phase was changed.

[0020]

The magnetoresistive element of the present invention uses a novel granular type tunnel magnetoresistive material, and has a magnetoresistance ratio of 9% or more at room temperature. Therefore, when the magnetoresistive element of the present invention is used, a large reproduction output is achieved with a magnetic field of 4 [KA / m] or less.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing a manufacturing process of a read element according to one embodiment of the present invention.

FIG. 2 is a table showing an insulating phase and a magnetoresistance ratio according to the present invention.

FIG. 3 is a graph citing a calculation result of an electronic state density of CrO ₂ .

[Explanation of symbols]

 1 quartz substrate, 24 Au electrode, 3 oxide film, 3 'granular film.

Claims (4)

[Claims] 1. A granular tunnel magnetoresistive material having a structure in which magnetic particles are dispersed in an insulator phase, wherein the magnetic particles have a rutile crystal structure. 2. The magnetoresistive element according to claim 1, wherein said magnetic particles are a chromium oxide having a rutile type crystal structure. 3. The method according to claim 1, wherein the insulator phase is a titanium oxide having a rutile crystal structure, a halide of M (M = magnesium, nickel, cobalt, iron, zinc, manganese), or an aluminum oxide or a silicon oxide. The magnetoresistive element according to claim 1, wherein the magnetoresistive element is composed of one or more types. 4. The size of the magnetic particles is 0.5 to 5 n.
The magnetoresistive element according to any one of claims 1 to 3, wherein m and the thickness of the insulating phase between the magnetic particles are 0.5 to 3 nm.