Stock material or miscellaneous articles – Composite – Of inorganic material
Reexamination Certificate
1998-10-22
2001-02-06
Kiliman, Leszek (Department: 1773)
Stock material or miscellaneous articles
Composite
Of inorganic material
C428S690000, C428S690000, C428S690000, C428S141000, C428S900000, C360S112000, C427S128000, C427S129000, C427S130000
Reexamination Certificate
active
06183890
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a magneto-resistance effect device (namely, an MR device), and in particular, to a magneto-resistance effect device which is capable of reproducing a desired recording information from a magnetic recording medium by the use of the magneto-resistance effect.
A magneto-resistance effect device (namely, an MR device) of the type described conventionally and widely has been used for a magnetic sensor, a magnetic head and an large-scale integrated circuit (namely, an LSI) memory.
Recently, a giant magneto-resistance (namely, GMR) effect has been developed, and has been widely applied for the industry field.
In this event, it has been conventionally and widely known that the spin scattering causes the magneto-resistance effect. Specifically, the phenomenon regarding the spin scattering results from the fact that an electron of up-spin has low scattering probability for an electron of the up-spin, and has high scattering probability for an electron of downspin.
In other words, the up-spin electron has low scattering probability in a magnetic domain of the up-spin while it has high scattering probability in different magnetic domain. As a result, the magneto-resistance effect takes place.
Therefore, it is required that a magnetization direction is variable in accordance with a change of a desired external magnetic field, and the domains of the up-spin and the down-spin coexist in the MR device in order to realize the MR effect in accordance with difference of the spin scattering. Namely, magnetization directions are different to each other in the respective domains.
In particular, when each magnetic domain has a magnetization direction of parallel opposite to each other, the MR effect indicates a maximum value. Therefore, it is important as a device parameter to realize the opposite parallel state under a low external magnetic field because the parameter relates to high sensitivity of the MR device.
Several methods have been so far reported in accordance with difference in structure to form the above-mentioned opposite parallel state.
For instance, devices, which utilize MR effect, are conventionally known, and are classified into (1) the MR devices formed by a granular film, (2) MR device formed by a metal multi-layer, (3) MR devices (magnetic bulb) of the spin-bulb type due to a sandwich structure via a tunnel barrier.
In the above-mentioned MR device formed by the granular film, ferromagnetic material, such as Fe, Co, and Ni, is precipitated or deposited in a non-magnetic layer, as disclosed in Japanese Unexamined Patent Publication No. Hei. 6-318749.
In this event, a precipitated state (namely, shape, size and direction of the precipitated particle) becomes irregular. More specifically, the precipitated particle has a long ellipse in accordance with a precipitated condition, and thereby, the size of the particle becomes random.
On the other hand, difference of one axis anisotropy or coercive force occurs for each precipitated particle by the randomness in size of the particles. Thereby, the MR effect brings about. At the same time, the magnetization is reversed under a low external magnetic field because the precipitated particle is small in size. In consequence, the MR device can operate under the low magnetic fields.
Subsequently, the MR effect due to the metal multi-layer has been disclosed in many papers. For example, the GMR effect caused by a multi-layer film consisting of iron and chromium is described in Physical Review Letter, 1998, volume 61, number 21, page 2472.
Further, the above-mentioned spin-bubble type MR device has been disclosed, for example, in Journal of Applied Physics, Aprl 1991, Vol. 69 (8), pages 4774-4779.
Specifically, MR devices having three layer structure have been suggested. In this case, the MR device utilizes the difference of the coercive force between a permalloy layer that is magnetically free and a permalloy layer that is magnetically pinned by a manganese layer.
However, ferromagnetic material, such as Fe, Co, and Ni, is precipitated in the non-magnetic electrical conductive layer in the conventional MR device of the granular type. In this event, it is difficult to control subtle differences of coercive force and precipitation particle density because the ferromagnetic material is naturally precipitated or deposited. In consequence, it is difficult to keep uniformity in manufacturing. As a result, the MR effect can not be essentially and sufficiently realized.
On the other hand, a large GMR effect of 200% or more at maximum is observed in the MR device of the metal multi-layer type. However, it is difficult to process the device because a current flows in a direction perpendicular to a plane.
Moreover, the resistance of the device is extremely low (approximately, several tens macro-ohm) because a practical device has a size of 0.24 micron in the perpendicular direction for the plane at several tens micron square.
In addition, an external magnetic field of several tesla is required to reverse the magnetization, and this is not a practical sensitivity.
Thus, there are a plurality of problems in putting conventional MR devices to practical use.
SUMMARY OF THE INVENTION
It is therefore an object of this invention to provide an MR device which is capable of artificially and readily controlling a magnetic domain of nano-meter size.
It is another object of this invention to provide an MR device which has high sensitivity and high gain.
According to this invention, a magneto-resistance effect device includes a plurality of magnetic dots. In this event, each of the magnetic dots is formed by magnetic material on a substrate and where a magneto-resistance effect occurs by applying an external magnetic field.
With such a structure, the magnetic dots are arranged on the substrate in a two-dimensional array. Herein, the two-dimensional array has a plurality of rows along a column direction and a plurality of columns along a row direction.
Further, the magnetic dots include at least first magnetic dots and second magnetic dots. In this case, the first magnetic dots are arranged on first rows while the second magnetic dots are arranged on second rows.
Under this circumstance, the first magnetic dot is different from the second magnetic dot in shape.
In this invention, the MR device having high sensitivity and high gain can be obtained because fine magnetic dots are arranged in the two-dimensional array. Further, the resistance of the MR device can be set to extremely high value as compared to the GMR device of the vertical plane type because the width of the device can be narrowed. For instance, the device resistance of the conventional laminate type MR device is micro-ohm per unit. In contrast, in the MR device according to this invention, device resistance of several hundreds-ohms can be obtained. Therefore, the MR device according to this invention has an advantage in matching with the LSI memory device.
As a result, the MR device according to this invention is applicable for a magnetic sensor itself, a magnetic head of a magnetic memory device, and a super high-integrated memory device of a data recording type, such as, a magnetic RAM.
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patent: 5585198 (1996-12-01), Maeda et al.
patent: 5738929 (1998-04-01), Maeda et al.
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Ootuka et al., “A new fabrication method of ultra small tunnel junctions”, Third Int'l Symposium . . . Dec. 4-8, 1995 vol. 227, p.p. 307-309.
Dieny et al., Magnetotransport properties of magnetically soft spin-valve structures (invited), J. Applk. Physics, vol. 69, No. 8, (1991), pp 4775-4779.
Baibich et al., Giant Magnetroresistance of (001) Fe/(001)Cr Magnetic Superlattices, Physical Review Letter, vol. 61, No. 21, (1988), pp 2472-2475.
Foley & Lardner
Kiliman Leszek
NEC Corporation
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