GB2301710A

GB2301710A - Giant magnetoresistance

Info

Publication number: GB2301710A
Application number: GB9611390A
Authority: GB
Inventors: Makoto Iijima
Original assignee: Fujitsu Ltd
Current assignee: Fujitsu Ltd
Priority date: 1995-06-01
Filing date: 1996-05-31
Publication date: 1996-12-11
Anticipated expiration: 2016-05-31
Also published as: DE19622040A1; KR970003289A; GB9611390D0; GB2301710B

Description

GIANT MAGNETORESISTANCE is 2301710 The present invention relates to a

giant magnetoresistive (GMR) element and a process of production thereof, more especially to a giant magnetoresistive element advantageously applicable to magnetic sensors such as a read head for reading information recorded on a magnetic disk at a density of more than 5 Gbit/in2.

Magnetoresistive (MR) heads are commercially used to read information recorded on magnetic disks at a high density by utilizing the magnetoresistance effect. MR heads are commonly made of Permalloy or of a Ni-Fe alloy. To read information recorded at an increased density of more than 5 Gbit/in2, read heads utilizing the giant magnetoresistance (GMR) effect are being studied.

The GMR effect is obtained by a combination of magnetic and non-magnetic metals. There are proposed different GMR structures including a multilayer structure composed of an alternate laminate of magnetic and non-magnetic metal layers, a spin valve structure utilizing a difference in magnetization of two magnetic layers, one having a fixed magnetization and the other unfixed magnetization, with a non-magnetic layer intervening therebetween, and a granular structure composed of magnetic metal grains dispersed in a matrix of a non-magnetic metal.

The granular structure is more advantageous than other two structures because it is easier to produce and has higher thermal stability, which is important for a production process for magnetic heads which includes heating steps.

US 5,366,815 discloses an MR element having a magnetic multilayer structure composed of an alternate is laminate of one or more magnetic layers comprising at least one selected. from Fe, Cc and Ni and one or more Ag layers, in which the magnetic and Ag layers are deposited to a thickness of 2A to 60A by molecular beam epitaxy under the conditions such that the deposited particles have a kinetic energy of 0.01 to 5 eV and a medium energy of 0.05 to 0.5 eV during deposition. The magnetic multilayer structure has an easy magnetization axis in a plane parallel to its surface and an in-plane square ratio of 0.5 or less and exhibits a ferromagnetism and a giant magnetoresistance effect at low magnetic fields, such as a magnetoresistance change of 1 to 40!k in a magnetic field of 0.01 to 20 kOe.

US 5,341,118 discloses a magnetic multilayer structure having a size which is a function of the nonmagnetic layer thickness, in which non- magnetic layers are composed of Cu or Ru and magnetic layers are composed of Co or Ni.

US 5,341,261 discloses a magnetoresistive sensor having a laminated structure composed of at least two bilayers each being composed of a first film of a ferromagnetic material and an adjoining second film of a non-magnetic material, a means for generating a current flowing through the sensor and a means for detecting a voltage change across the sensor due to a resistivity change of the sensor as a result of a rotation of magnetization direction in the first film as a function of an external magnetic field to be detected. The said first films of the ferromagnetic material each contain at least one material layer having a thickness of one or several monolayers and located at a distance X from the adjoining interface. The laminate structure is expressed by [F/NM]n in which F is a film of a ferromagnetic material such as Fe or Cc and NM is a spacer layer of a non-magnetic material such as Cr or Cu.

Japanese Unexamined Patent Publication (Kokai) No. 6-326377 discloses a granular multilayer MR element provided with an MR sensing element including one or more discontinuous layers or quasicircular grains of a ferromagnetic material embedded in a non-magnetic electrically conductive material. The granular multilayer MR element is produced by a process including a step of depositing, on a substrate, plural double-layer structures including a first layer of the non-magnetic electrically conductive material and a second layer of the ferromagnetic material and a step of annealing the thus-deposited multilayer structure at a selected temperature to cause the second layer of the ferromagnetic material to decompose to form plural ferromagnetic grains and to cause the nonmagnetic material of the first layer to flow or diffuse between and surround the ferromagnetic grains. The ferromagnetic grains consist of a ferromagnetic material selected from Fe, Co, Ni, NiFe and ferromagnetic alloy based on Fe, Co, Ni and NiFe. The non-magnetic material consists of Ag, Au, Cu or Ru. The ferromagnetic grains have a thickness of about 10A to about 30A. The non-magnetic electrically conductive layer has a thickness of from about 10A to about 50A. In the above-mentioned JP-A-6326377, the ferromagnetic grains and the surrounding non-magnetic material collectively form a discontinuous magnetic layer of the grains laminated with a non-magnetic layer of the non-magnetic material, as can be best seen from Fig. 2 of this publication. The ferromagnetic grains have the form of quasicircular platelets having a thickness which determines, and is therefore equal to, the thickness of the magnetic layer to form the discontinuous magnetic layer having that thickness.

Journal of Magnetism and Magnetic Materials 114, 1992, L230 - L234 disclosed a non-laminated structure is of a Cox-Agl_x alloy film (x = 0.25 - 0.56) having a thickness of 70 - 100 nm, which was formed by DC magnetron sputtering using a composite target at room temperature and exhibited a maximum MR ratio of greater than 17t at room temperature.

J. Appl. Phys. 70, 1991, 5862 - 5884 disclosed a nano-structure Co/Ag composite film of a COSOA950 alloy (39 volt Co) including 30A to 297A Co crystals and 39A to 423A Ag crystals, which was formed by a magnetron sputtering using a mixed Co/Ag sintered target at a substrate temperature of 100 to 6000C and exhibited a maximum coersive force of 565 Oe at 6K.

Physical Review Letters, vol. 166, 1991, 3060 3063 disclosed a perpendicular GMR exhibited by an Ag/Co multilayer structure at 4.2K. The Ag layer had a thickness of 2 to 60 nm and the Co layer had a thickness of 6 to 15 nm.

Japanese Unexamined Patent Publication (Kokai) No. 6-318749 disclosed an MR element having a magnetic layer composed of fine grains of an amorphous magnetic metal including at least one of Fe, Co and Ni dispersed in a noble metal matrix of Cu, Ag, or Au. Also disclosed is an MR element having a laminate structure including a magnetic layer composed of fine grains of a crystalline or amorphous magnetic metal including at least one of Fe, Co and Ni and a non-magnetic layer including a noble metal. To form the laminate structure, a magnetic layer composed of at least one of Fe, Co and Ni and a non-magnetic layer are alternately deposited and the as-deposited laminate is then heat-treated to cause the noble metal to flow or diffuse into the magnetic layer. The magnetic layer has a thickness of 5 to 200A and the non-magnetic layer has a thickness of 10 to 100A. The number of the laminated layers is about 5 to 50.

This Japanese publication describes, as a preferred example, a 100A thick magnetic layer of an A975CO25 granular alloy laminated with a 50A thick Ag non-magnetic layer. The low Co content of 25 at% is believed to be selected as an optimum value to maximize the magnetic interaction between the Co magnetic grains in the Ag-Co granular alloy magnetic layer based on the established concept for optimizing the chemical composition of the non-laminated GMR element composed of a Ag-Co granular alloy only. This concept does not lead to the high Co content of from 55 at% to 80 at-O. of the present invention, which is necessary to develop an antiferromagnetic coupling between magnetic layers, not between magnetic grains in a magnetic layer, in order to achieve an improved sensitivity of a GMR element.

The magnitude of the GMR effect, particularly in GMR elements using a granular alloy, depends on the size and shape of the magnetic metal grains and the operating temperature. The magnetic metal grains each forms a single magnetic domain and the magnetization direction of the grain varies with temperature. Therefore, the granular alloy requires a high external magnetic field of several to several tens of koe for aligning the magnetization directions of the magnetic grains. This is a substantial drawback of the GMR element using a granular alloy when applied to a read head for magnetic disks, which must have good sensitivity at low magnetic fields of several tens of Oe.

According to a first aspect of the present invention, there is provided a giant magnetoresistive element comprising:

an alternate laminate of magnetic and non-magnetic layers, the alternate laminate being composed of plural magnetic/non-magnetic laminate units each composed of one magnetic layer and one non-magnetic layer; the magnetic layers being composed of a granular is alloy consisting of numerous fine grains of a magnetic metal and a matrix of a first non-magnetic metal, the fine grains being sufficiently small in size to form a single magnetic domain and being dispersed in the matrix in a density sufficient to provide an antiferromagnetic coupling between each neighbouring pair of the magnetic layers; and the non-magnetic layers being composed of a second non-magnetic metal.

By contrast, it is noted that formation of the magnetic grains as relatively large quasicircular platelets as in the above-mentioned JP-A-6326377 does not result in a single magnetic domain as in the first aspect of the present invention.

With preferred embodiments of the invention it is therefore possible to provide a giant magnetoresistive element having an improved sensitivity at low magnetic fields by having a magnetic/non-magnetic laminate structure including magnetic layers composed of a granular structure or granular alloy in which antiferromagnetic coupling between neighbouring magnetic layers is developed while the interaction between fine grains in the magnetic layer is controlled. The herein used term "sensitivity" means, if not otherwise specified, the magnetic field sensitivity defined as a magnetoresistance change per unit magnetic field, which can be expressed in 110.-/Oell.

In a preferred embodiment of the giant magnetoresistive element, the granular alloy contains the fine grains of the magnetic metal in a density or concentration of 55 to 80 at% in terms of the concentration of the magnetic metal in the granular alloy. This range of the density of the fine grains has been found to advantageously facilitate or develop the antiferromagnetic coupling between the neighbouring magnetic layers while controlling the interaction is between the magnetic grains in the magnetic layers, thereby enhancing the giant magnetoresistance effect.

If on the one hand the grain density is less than 55 at-., the antiferromagnetic coupling is found to be generally not strong enough to enhance the giant magnetoresistance effect. Lower grain densities also have the disadvantage that the grain size is small enough to cause significant superparamagnetism effects which makes it difficult for the magnetic fine grains to change in the magnetization direction in response to a change in the external magnetic field.

If on the other hand the grain density is more than 80 at%, the magnetic fine grains are brought into contact with each other and form larger grains having irregular shapes, in which plural magnetic domains are formed which decrease the sensitivity and induce Barkhausen noise.

The alternate lamination of the magnetic and nonmagnetic layers is preferably composed of 5 to 7 magnetic/non-magnetic laminate units (i.e. periods). To develop an antiferromagnetic coupling between neighbouring magnetic layers of a granular alloy, the alternate laminate must be composed of at least two magnetic/non-magnetic laminate units. There is however little advantage to be gained in increasing the number of the magnetic/non-magnetic laminate units beyond much more than 10 because the incremental increase in the MR ratio and sensitivity resulting from an increase in the number of lamination periods becomes small. Moreover, the size of the alternate laminate, and thus of a magnetic head, incorporating such a laminate, increases and this increase in size may be undesirable in some applications.

The magnetic layer composed of a granular alloy preferably has a thickness of 15A to SOA, more preferably 15A to 30A. This range of the magnetic layer thickness advantageously limits the size of the magnetic fine grains to 50A or less and ensures that each of the magnetic fine grains form a single magnetic domain. If the magnetic layer is too thick, the magnetic fine grains grow too large and plural magnetic domains are formed in the grains and cause Barkhausen noise to occur or the sensitivity to be decreased.

Preferably, the alternate laminate has a thickness of 400A or less. This is particularly preferable if a GMR element or magnetic sensor is to be used to fabricate a read head for an advanced high density record of 5 Gbit/in2 or more.

The individual non-magnetic layers preferably have respective thicknesses of 10A to 50A to advantageously develop the antiferromagnetic coupling between each nearest neighbour pair of magnetic layers between which a non-magnetic layer is interposed.

Preferably, the magnetic metal is selected from the group consisting of Ni, Co, Fe and alloys thereof and the first non-magnetic metal composing the matrix and the second non-magnetic metal composing the non-magnetic layers are selected from the group consisting of Cu, Ag, Au, Pt and alloys thereof.

The magnetic layers composed of the granular alloy as defined above have no magnetic anisotropy relative to an external magnetic field. There is thus a high degree of freedom in designing devices using GMR elements embodying the present invention.

According to a second aspect of the present invention there is provided a magnetic sensor comprising a giant magnetoresistive element according to the first aspect of the invention.

A magnetic sensor according to the second aspect of the present invention typically includes a film of the giant magnetoresistive element (GMR film), a magnetic metal film disposed close to the GMR film for -gproviding a biasing magnetic field, a pair of electrodes connected to the GMR film at two selected points for supplying a constant current to the GMR film and a detector for detecting a voltage generated between the electrodes.

The GMR element and the magnetic sensor according to the first and second aspects of the invention are advantageously applied to a magnetoresistive (MR) sensor having a laminate structure composed of at least two doublelayer units, each being composed of a first film of a ferromagnetic material and an adjoining second film of a non-magnetic material, a means for generating a current flowing through the sensor and a means for detecting a vcltage change across the sensor due to a resistivity change of the sensor as a result of a rotation of magnetization direction in the first film as a function of an external magnetic field to be detected.

According to a third aspect of the present invention there is provided a process of producing a giant magnetoresistive element, the process comprising alternately depositing, on a substrate, a first layer of a solid solution of a magnetic metal and a first non-magnetic metal and a second layer of a second nonmagnetic metal to form an as-deposited laminate, the magnetic metal being present in the solid solution in an amount corresponding to the density of the numerous fine grains of the magnetic metal that is desired in the first layers subsequent to the following step of heat-treating the as-deposited laminate to cause, in the first layer, the magnetic metal to precipitate from the solid solution to form numerous fine grains of the magnetic metal, which grains are sufficiently small in size to each form a single magnetic domain and are dispersed in a matrix of the first non-magnetic metal, the numerous fine grains and the matrix composing a granular alloy, thereby forming an alternate laminate of a magnetic layer of the granular alloy and a non-magnetic layer of the second non-magnetic metal. The proportion of the magnetic material to be incorporated in the as-deposited first layers is preferably selected with a view to producing a desired level of antiferromagnetic coupling between nearest neigbour first layers subsequent to the postdeposition heat-treatment.

In the process according to the third aspect of the present invention, the step of alternate deposition is preferably carried out by any of sputtering, ion beam sputtering, molecular beam epitaxy, and combinations thereof. The substrate on which the magnetic and non-magnetic layers are deposited may be any of glass, silica glass, silicon and ceramics. The step of heat treating the as-deposited laminate causes a phase separation in the as-deposited solid solution of the magnetic metal and the first non-magnetic metal, in which a homogeneous solid solution forming a single phase is separated into two distinct phases, one being numerous fine magnetic metal grains of the magnetic metal and the other being a non-magnetic metal matrix of the first non-magnetic metal.

To deposit the first layers, which will form the magnetic layers of the granular alloy of the alternate laminate, a sputtering target or a molecular beam source may be made of an alloy consisting of any one nonmagnetic metal of Cu, Ag, Au and Pt, or alloys thereof and any one magnetic metal of Ni, Cc and Fe, or alloys thereof. The sputtering target may also be in a composite form composed of small chips, strips, flakes or foils of the magnetic metal placed on a base of the non-magnetic metal.

To deposit the second layer of the second nonmagnetic metal, which will form the non-magnetic layers of the alternate laminate, another sputtering target or molecular beam source is made of any of the above-recited non-magnetic metals.

The sputtering targets or molecular beam sources for the first and second layers are alternately used to deposit the alternate laminate of the first and second layers.

Preferably, the first and second layers are deposited in one and the same vacuum chamber in order to provide good bond between these layers in the as deposited state, as well as between the magnetic granular alloy layer and the non-magnetic metal layer after heat treatment.

The magnetic metal is present in an atomic form in the solid solution in the as-deposited state, and when the solid solution is heat-treated, the atoms then aggregate to form fine grains of the magnetic metal, thereby forming a granular alloy composed of numerous fine magnetic metal grains dispersed in a matrix of the non-magnetic metal, i.e. the heat treatment causes rearrangement of atoms in the solid solution (the first layers) such that the single phase of the solid solution is separated into two distinct phases of the numerous magnetic metal grains and the nonmagnetic metal matrix.

An interlayer rearrangement or diffusion of atoms between the first layer of the solid solution and the second layer of the second non-magnetic metal occurs to a considerably lesser extent than those within the first layer, resulting in the formation of a mutual diffused zone in a minute amount, if any, which has no substantial influence on the formation of the alternate laminate of distinct magnetic and non-magnetic layers in which a non-magnetic layer of the second non-magnetic metal is interposed between magnetic layers composed of a granular alloy consisting of numerous fine grains of the magnetic metal dispersed in a matrix of the first non-magnetic metal, thereby ensuring that the alternate laminate of magnetic and non-magnetic layers exhibits the giant magnetoresistive (GMR) effect.

The heat treatment is preferably carried out in vacuum, hydrogen gas, nitrogen gas, or inert gas to prevent oxidation of metals. An optimum heat treatment temperature may be determined in accordance with the alloy composition, the as-deposited thickness, the heating rate and the heating time.

For a better understanding of the invention, and to show how the same may be carried into effect, reference will now be made, by way of example only, to the accompanying drawings, in which:- Fig. 1 schematically illustrates a giant magnetoresistive (GMR) element according to an embodiment of the present invention in a cross-sectional view; Fig. 2 is a graph showing a magnetoresistance (MR) curve for the GMR element shown in Fig. 1; Fig. 3 is a graph showing the MR ratio and the saturation magnetization Hs of a GMR element as a function of the Co content of the granular alloy forming a magnetic layer; Fig. 4 is a graph showing an MR curve of a GMR element having an alternate laminate structure according to an embodiment of the present invention in comparison with that of a non-laminated single layer GMR element, before and after annealing treatment; Fig. 5 is a graph showing an MR curve of a GMR element according to an embodiment of the present invention in comparison with those of conventional GMR elements; Fig. 6 is a graph showing the MR ratio of GMR element according to an embodiment of the present invention as a function of the thickness of a non-magnetic Cu layer; Fig. 7 schematically illustrates a magnetic sensor according to an embodiment of the present invention in a cross-sectional; and Fig. a is a schematic perspective view of the magnetic sensor shown in Fig. 7. Examvle 1 Figure 1 shows an alternate laminate structure of a GMR element according to a first example. The alternate laminate shown in Fig. 1 was produced by the following process.

An adhesive layer 6 of Ta or Ti was first formed on a glass substrate 5, and on the layer 6, a Co-Ag alloy layer 3 and a Cu layer 4 were then alternately formed layer by layer to deposit ten layers, respectively, i. e., ten pairs of Co-Ag alloy layers 3 and Cu layers 4 were deposited sequentially as noted by "X1011 in Fig. 1. More specifically, a 20A thick alloy layer 3 of a C066A934 solid solution and a 25A thick Cu layer 4 were alternately deposited by sputtering (back pressure: 5 x 10-5 Pa and Ar: 0.1 Pa). To sputter the C066A934 alloy, a target made of a blended compact of Co and Ag powders in a proportion of 66 at% and 34 atoi was used. The as-deposited laminate was heat treated in a vacuum of 2 x 10-8 Torr with a heating rate of 10 OC/minute at a holding temperature of 4000C for a holding time of 1 hour, followed by furnace cooling to room temperature. By this heat treatment Co-Ag alloy layer 3, which was initially a solid solution, was converted to a Co-Ag granular alloy 3 composed of numerous fine grains 1 of Co dispersed in matrix 2 of Ag.

Figure 2 shows MR curves of the above-produced GMR element having a Ti adhesive layer 6 determined by a DC four-probe method in a range of the external magnetic is field of 1000 Oe. An MR ratio of 7.4% was achieved in an external magnetic field range of 30 Oe. A sensitivity of 0.1 %/Oe was determined from the slope of the MR peak, which is fifteen times greater than that obtained by an MR element composed of a granular alloy alone.

The same MR curves were obtained for both of the current directions perpendicular to and parallel with the direction of the external magnetic field, which shows that this GMR element has no magnetic anisotropy. This provides an increased degree of freedom in designing magnetic sensors using the GMR element, such as read heads for magnetic disks, thus facilitating the design of devices incorporating GMR elements.,Example 2

GMR elements according to a second example were produced under the same conditions as used for the first example, except for the following points. The as-deposited laminates had 16A thick Co-Ag alloy layers and 40A thick Cu layers with a 50A thick Ta adhesive layer and different Co contents in the Co-Ag alloy of from 50 to 100 at% Co. To sputter the Co- Ag alloys having different Co contents, targets made of a blended compact of Co and Ag powders in proportions corresponding to the alloy compositions were used. The as-deposited laminates were annealed at 3000C for I hour followed by furnace cooling to room temperature.

Figure 3 shows the MR properties of the thusproduced GMR elements plotted against the Co content of the Co-Ag magnetic layer. It can be seen from Fig. 3 that the MR ratio monotonically increases as the Co content increases while the saturation magnetization Hs sharply decreases when the Co content increases up to 55 at%, and then, the Hs gradually increases with the increase of the Co content. It is noted that saturation magnetization Hs represents the sensitivit -is- of the GMR element. Therefore, to achieve an improvement in both the MR ratio and the sensitivity, the Co content is preferably 55 at% or more. It should also be taken into consideration that, if the grain density or concentration is more than 80 atok, the magnetic fine grains are brought into contact with each other to form large grains having irregular shapes, in which plural magnetic domains are formed to decrease the sensitivity and induce Barkhausen noise to occur.

Therefore, the Co content is preferably within the range of from 55 at% to 80 at%. Examnle 3 The MR properties were also compared between a GMR element embodying the invention, having an alternate laminate composed of Co-Ag granular alloy layers and Cu non-magnetic layers, and a comparative GMR element having a non-laminated structure composed of the same Co-Ag granular alloy only.

The GMR element of this example has the alternate laminate structure shown in Fig. 1 and was produced under substantially the same conditions as used in Example 1, except for the following changes. The as-deposited laminates had 20A thick C066A934 alloy layers and 25A thick Cu layers with SOA thick Ta adhesive layer. The as-deposited laminate was annealed at 3000C for 1 hour followed by furnace cooling to room temperature.

The comparative GMR element was produced by only forming a Co-Ag alloy layer having the same composition as used above and the same thickness as the total thickness of the alternate laminate structure as described above. The as-deposited sample was annealed under the same conditions as used above.

Figure 4 shows MR curves measured for both the asdeposited and annealed samples. In the as-deposited state, the GMR element of this example exhibited a weak is GMR effect due to a weak antiferromagnetic coupling between the layers of the Co-Ag solid solution, and when annealed at 3000C, exhibited a remarkably enhanced GMR effect due to precipitation of fine Co grains from the solid solution, i.e. conversion from the Co-Ag solid solution to a Co-Ag granular alloy.

The comparative sample exhibited merely a slight GMR effect even after the annealing at 3000C.

The desirable properties displayed by the GMR element of this example are attributable to the alternate laminate structure of magnetic and nonmagnetic layers in which structure a non-magnetic layer of Cu intervenes between magnetic layers of the Co-Ag granular alloy to provide an extensive magnetic/nonmagnetic interface which advantageously develops the antiferromagnetic coupling between the magnetic layers. Example 4 The MR properties were compared between a GMR element having an alternate laminate structure as shown in Fig. 1 comprising paired granular C066A934 alloy magnetic layers and Cu non-magnetic layers and two conventional GMR elements, one having an alternate laminate structure of Co magnetic layers and a Cu non-magnetic layers and the other having a non-laminate structure composed of a granular C041A934 alloy only.

Figure 5 shows MR curves for these three samples.

As shown by the fine broken line, the conventional GMR element having the Cc/Cu alternate laminate structure provides a large MR ratio of 25% but has a large hysteresis and a low sensitivity (slope of the MR peak) at low magnetic fields.

The conventional GMR element having the granular 41at%-Co-59at'iAg alloy non-laminated structure, shown by the thick broken line, has a small MR ratio and sensitivity and also has a large hysteresis. The GMR element of this example having the is alternate laminate of

magnetic layers of the granular Co-Ag alloy and non- magnetic Cu layers, shown by the solid line, exhibites an improved sensitivity and a decreased hysteresis although the MR ratio is not remarkably large. ExamiDle 5 GMR elements having an alternate laminate structure as shown in Fig. 1 comprising Co 66A934 granular alloy magnetic layers and Cu non-magnetic layers were produced under the same conditions as used in Example 1, except that the thickness of the Cu layer was varied over the range of 20A to 40A.

Figure 6 shows the MR ratio of the thus-produced GMR elements as a function of the Cu layer thickness.

As can be seen from Fig. 6, the MR ratio depend s on the Cu layer thickness within the range of 20A to 40A and a maximum MR ratio is obtained for a Cu layer thickness of 25A. Namely, an optimum Cu layer thickness is 25A in this specific sample. ExamiDle 6 A magnetic sensor embodying the present invention was produced in the following process sequence.

Referring to Figs. 7 and 8, an alternate laminate 8 having the same structure of that produced in Example I was formed on a Si substrate by a process substantially the same as that used in Example 1. Namely, the alternate laminate 8 included ten pairs of a 20A C066A934 granular alloy magnetic layer and a 25A Cu non-magnetic layer. More specifically, a 200A N'77Fej8Cr. biasing film 10 and a 150A Ta adhesive layer 9 were first formed on a Si substrate 11, in that order, and the alternate laminate 8 was then formed on the Ta adhesive layer 9. The alternate laminate 8, together with the adhesive layer 9 and the biasing film 10, was then patterned to a dimension of lAm x 0.2gm x 450A. Cu electrodes 7 were formed on both ends of the alternate laminate 8.

A detection current of 5 mA was applied to the Cu electrodes 7. The resistance change measured at an external magnetic field within a range of 100 Oe was 800 MV in terms of the voltage change.

is

Claims

CLAIMS:

1. A giant magnetoresistive element comprising:

a laminate of magnetic and non-magnetic layers, the laminate comprising a plurality of laminate subsections each having one magnetic layer and one non-magnetic layer; the magnetic layers comprising a granular alloy consisting of numerous fine grains of a magnetic metal in a matrix of a first non-magnetic metal, the fine grains being sufficiently small in size to form a single magnetic domain and being dispersed in the matrix in a density sufficient to provide an antiferromagnetic coupling between each neighbouring pair of the magnetic layers; and the non-magnetic layers comprising a second non-magnetic metal.

2. An element according to claim 1, wherein the granular alloy contains the fine grains of the magneti metal in a density of 55 to 80 at% in terms of the concentration of the magnetic metal in the granular alloy.

3. An element according to claim 1 or 2, wherein the laminate comprises 5 to 7 laminate subsections.

4. An element according to claim 1, 2 or 3, wherein the laminate has a thickness of 400A or less.

5. An element according to any one of the preceding claims, wherein the magnetic layers of the laminate each have a thickness of between 15A and 50A.

6. An element according to any one of the preceding claims, wherein the non-magnetic layers of the laminate each have a thickness of between 10A and 50A.

7. An element according to any one of the preceding claims, wherein the magnetic metal is selected from the group Ni, Cc, Fe, and alloys thereof.

8. An element according to any one of the c preceding claims, wherein the first non-magnetic metal is a different metal from the second non-magnetic metal.

9. An element according to any one of the preceding claims, wherein the first non-magnetic metal and the second non-magnetic metal are selected from the group Cu, Ag, Au, Pt, and alloys thereof.

10. A giant magnetoresistive element substantially as hereinbefore described in any one of Examples 1 to 6 with reference to Figure 1 of the accompanying drawings.

11. A magnetic sensor comprising a giant magnetoresistive element according to any one of the preceding claims.

12. A magnetic sensor substantially as hereinbefore described with reference to Figures 7 and 8 of the accompanying drawings, the sensor comprising a giant magnetoresistive element according to claim 10.

13. A process of producing a giant magnetoresistive element, comprising the steps of:

alternately depositing, on a substrate, a first layer of a solid solution of a magnetic metal and a first non-magnetic metal and a second layer of a second non-magnetic metal to form an as-deposited laminate; and heat-treating the as-deposited laminate to cause, in the first layers, the magnetic metal to precipitate from the solid solution to form numerous fine grains of the magnetic metal, which grains are sufficiently small in size to each form a single magnetic domain and are dispersed in a matrix of the first non-magnetic metal, the numerous fine grains and the matrix composing a granular alloy, thereby forming a laminate of magnetic layers of the granular alloy and non-magnetic layers of the second non-magnetic metal.

14. A process according to claim 13, wherein the h density of the numerous fine grains of the magnetic metal in the matrix of the first non-magnetic metal is 55 to 80 at% in terms of the amount of the magnetic metal in the solid solution.

15. A process according to claim 13 or 14, wherein the step of alternate deposition is carried out by any of sputtering, ion beam sputtering and molecular beam epitaxy.

16. A process according to claim 13, 14 or 15, wherein the substrate is made of a material selected from the group: glass, silica glass, silicon and ceramic.

17. A process substantially as hereinbefore described in any of Examples 1 to 6 with reference to Figure 1 of the accompanying drawings.