Static information storage and retrieval – Systems using particular element – Magnetoresistive
Reexamination Certificate
2000-07-10
2001-07-03
Mai, Son (Department: 2818)
Static information storage and retrieval
Systems using particular element
Magnetoresistive
C365S171000, C365S173000
Reexamination Certificate
active
06256222
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a magnetoresistance effect device, and also relates to a magnetic head, a memory device, and an amplifying device using such a magnetoresietance effect device.
2. Description of the Related Art
A magnetoresistive sensor (hereinafter referred to as an MR sensor) and a magnetoresistive head (hereinafter referred to as an MR head) using a magnetoresistance effect device have been under development. The term “a magnetoresistance effect element” indicates a device which varies an electric resistance depending on the magnetic field externally applied. The characteristic of the magnetoresistance effect device is generally represented by a ratio of change of magnetoresistance (hereinafter abbreviated as an MR ratio). The MR ratio is defined by the following equation:
MR ratio (%)=(R(maximum)−R(minimum))/R(minimum)×100,
where R(maximum) and R(minimum) denote the maximum value and the minimum value of the resistance of the magnetorealstance effect device when a magnetic field is applied to the magnetoresistance effect device. Conventionally, as a material for a magnetoresistance effect device, a permalloy of Ni
0.5
Fe
0.2
is mainly used as the magnetic body. In the case of such magnetoresistance effect materials, the MR ratio is about 2.5%. In order to develop an MR sensor and an MR head with higher sensitivity, a magnetoresistive device exhibiting a higher MR ratio is required. It was recently found that [Fe/Cr] and [Co/Ru] artificial multilayers in which anti-ferromagnetic coupling is attained via a metal non-magnetic thin film such as Cr and Ru exhibit a giant magnetoresistance (GMR) effect in a ferromagnetic field (1 to 10 kOe) (see Physical Raview Latter Vol 61, p. 2472, 1988; and Physical Review Letter Vol. 64, p. 2304, 1990). However, these artificial multilayers require a magnetic field of several kilooersteds to several tens of kOe in order to attain a large MR change, so that such artificial multilayers cannot be practically used for a magnetic head and the like.
It was also found that an [Ni—Fe/Cu/Co] artificial multilayer using magnetic thin films of Ni—Fe and Co having different coercive forces in which they are separated by a metal non-magnetic thin film of Cu and are not magnetically coupled exhibits a GMR effect, and an artificial multllayer which has an MR ratio of 8% when a magnetic field of 0.5 kOe is applied at room temperature has been hitherto obtained (see Journal of Physical Society of Japan, Vol. 59, p. 3061, 1990). However, as is seen from the typical MR curve of this type of artificial multilayer shown in
FIG. 11
, a magnetic field of about 100 Oe is required for attaining a large MR change. Moreover, the MR asymmetrically varies from the negative magnetic field to the positive magnetic field, i.e., the MR exhibits poor linearity. That is, such an artificial multilayer has characteristics which are difficult to use in practice.
Also, it was found that [Ni—Fe—Co/Cu/Co] and [Ni—Fe—Co/Cu] artificial multilayers using magnetic thin films of Ni—Fe—Co and Co in which RKKY-type anti-ferro-magnetic coupling is attained via Cu exhibit a GMR effect, and an artificial multilayer which has an MR ratio of about 15% when a magnetic field of 0.5 kOe is applied at room temperature has been hitherto obtained (see Technical Report by THE INSTITUTE OF ELECTRONICS, INFORMATION AND COMMUNICATION ENGINEERS of Japan, MR91-9). As is seen from the typical MR curve of this type of artificial multilayer shown in
FIG. 12
, the MR substantially linearly varies from zero to the positive magnetic field, so that the film has characteristics which are sufficient for the application to an MR sensor. However, in order to get a large MR change, a magnetic field of about 50 Oe is required. Such a characteristic of the film is not appropriate for the application to an MR magnetic head which is required to be operated at most at 20 Oe and preferably less.
As a film which can be operated in a very weak magnetic field to be applied, a spin-valve type film in which Fe—Mn as an anti-ferromagnetic material is attached to Ni—Fe/Cu/Ni—Fe has been proposed (see Journal of Magnetism and Magnetic Materials 93, p. 101, 1991). As is seen from the typical MR curve of this type shown in
FIG. 13
, the operating magnetic field is actually weak, and a good linearity is observed. However, the MR ratio is as small as about 2%, and the Fe—Mn film has a poor corrosion resistance. The Fe—Mn film has a low Neel temperature, so that the device characteristics disadvantageously have great temperature dependence.
On the other hand, as a memory device using a magnetoresistance effect, a memory device using a conductor portion (sense lines) made of Ni—Fe(—Co)/TaN/Ni—Fe(—Co) in which Ni—Fe or Ni—Fe—Co as a conventional MR (magnetoresistance effect) material is laminated via TaN has been proposed (see U.S. Pat. No. 4,754,431, and IEEE Trans. Magn. Vol. 27, No. 6, 1991, pp. 5520-5522). Such a memory device utilizes the conventional material as an MR material, so that the MR ratio is 2% to 3%. Thus, the memory device has disadvantages in that the output during the information read-out is weak, and it is inherently difficult to perform nondestructive read-out.
SUMMARY OF THE INVENTION
The magnetoresistance effect device of this invention, includes a substrate; and a multilayer structure formed on the substrate, the multilayer structure including a hard magnetic film, a soft magnetic film, and a nonmagnetic metal film for separating the hard magnetic film from the soft magnetic film, wherein a magnetization curve of the hard magnetic film has a good square feature, and a direction of a magnetization easy axis of the hard magnetic film substantially agrees to a direction of a magnetic field to be detected.
In one embodiment of the invention, the multilayer structure has a structure in which the hard magnetic film, the soft magnetic film, and the non-magnetic metal film are stacked a plurality of times.
In another embodiment of the invention, a further magnetic film is inserted on both faces or on one face of the hard magnetic film, a thickness of the magnetic film is in the range of 0.1 to 2 nm, and the magnetic film includes at least one element selected from Co, Ni, and Fe as a main component.
In still another embodiment of the invention, the multilayer structure has a structure in which the hard magnetic film, the soft magnetic film, the non-magnetic metal film, and the inserted magnetic film are stacked a plurality of times.
In still another embodiment of the invention, a further magnetic film is inserted at, at least one of interfaces between the hard magnetic film and the non-magnetic metal film and between the soft magnetic film and the non-magnetic metal ffilm, a thickness of the magnetic film is in the range of 0.1 to 1 nm, and the magnetic film includes Co as a main component.
In still another embodiment of the invention, the multilayer structure has a structure in which the hard magnetic film, the soft magnetic film, the non-magnetic metal film, and the inserted magnetic film are stacked a plurality of times.
In still another embodiment of the invention, the soft magnetic film includes Ni
X
Co
Y
Fe
Z′
as a main component, and in an atomic composition ratio, X is in the range of 0.6 to 0.9, Y is in the range of 0 to 0.4, and Z is in the range of 0 to 0.3.
In still another embodiment of the invention, the soft magnetic film includes Ni
X′
Co
Y′
Fe
Z′
as a main component, and in an atomic composition ratio, X′ is in the range of 0 to 0.4, Y′ is in the range of 0.2 to 0.95, and Z′ is in the range of 0 to 0.5.
In still another embodiment of the invention, the soft magnetic film is an amorphous magnetic film.
In still another embodiment of the invention, the non-magnetic metal film is made of a material selected from Cu, Ag, and Au.
In still another embodiment of the invention, the non-magnetic metal film is made of Cu.
In sti
Irie Yousuke
Kawawake Yasuhiro
Sakakima Hiroshi
Satomi Mitsuo
Mai Son
Matsushita Electric - Industrial Co., Ltd.
Renner , Otto, Boisselle & Sklar, LLP
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