Dynamic magnetic information storage or retrieval – Head – Magnetoresistive reproducing head
Reexamination Certificate
1997-11-26
2003-03-18
Davis, David (Department: 2652)
Dynamic magnetic information storage or retrieval
Head
Magnetoresistive reproducing head
Reexamination Certificate
active
06535362
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to a magnetoresistive device and a magnetoresistive head. More particularly, the present invention relates to a magnetoresistive device in which a magnetoresistance is greatly changed in a low magnetic fields, and to a magnetoresistive head which is configured using such a magnetoresistive device and is suitable for high-density magnetic recording and reproducing operations.
2. Description of the Related Art
A magnetoresistive sensor (hereinafter, simply referred to as an “MR sensor”) and a magnetoresistive head (hereinafter, simply referred to as an “MR head”) using a magnetoresistive device have been under development. Conventionally, a permalloy made of Ni
0.8
Fe
0.2
and an alloy film made of Ni
0.8
Co
0.2
are mainly used as magnetic materials for these devices. The ratio of change in magnetoresistance (hereinafter, simply referred to as an “MR ratio”) of these magnetoresistive materials is about 2.5%. In order to develop a magnetoresistive device exhibiting a higher sensitivity, a magnetoresistive material having a higher MR ratio is required.
It was recently found that [Fe/Cr] and [Co/Ru] multilayers in which an antiferromagnetic coupling is attained via a metal non-magnetic thin film made of Cr or Ru exhibit a giant magnetoresistance effect in a ferromagnetic field (about 1 to about 10 kilo-oersteds (kOes)) (Physical Review Letter Vol. 61, p. 2472, 1988; and Physical Review Letter Vol. 64, p. 2304, 1990).
However, since these artificial multilayers require a magnetic field having an intensity of several to several tens of kOes in order to obtain a large MR change, such artificial multilayers cannot be practically applied to a magnetic head and the like.
In addition, it was also found that an [Ni—Fe/Cu/Co] artificial multilayer using magnetic thin films made of Ni—Fe and Co having different coercivities in which they are separated by a metal non-magnetic thin film made of Cu and which are not magnetically coupled to each other exhibits a giant magnetoresistance effect, and a magnetoresistive material which has an MR ratio of about 8% when a magnetic field an intensity of about 0.5 kOe is applied at room temperature was obtained (Journal of Physical Society of Japan, Vol. 59, p. 3061, 1990).
However, in the case of using a magnetoresistive material of such a type, a magnetic field having an intensity of about 100 Oes is required for obtaining a large MR change. Moreover, the magnetoresistance thereof asymmetrically varies from the negative magnetic field to the positive magnetic field. i.e. the magnetoresistance thereof exhibits a poor linearity. Thus, such a magnetoresistive material has characteristics which are not suitable for practical use.
Moreover, it was also found that [Ni—Fe—Co/Cu/Co] and [Ni—Fe—Co/Cu] artificial multilayers using magnetic thin films made of Ni—Fe—Co and Co in which an RKKY-type antiferromagnetic coupling is attained via Cu exhibit a giant magnetoresistance effect, and a magnetoresistive material which has an MR ratio of about 15% when a magnetic field having an intensity of about 0.5 kOe is applied at room temperature was obtained (Technical Report by THE INSTITUTE OF ELECTRONICS, INFORMATION AND COMMUNICATION ENGINEERS of Japan, MR91-9).
However, in the case of using a magnetoresistive material of such a type, the magnetoresistance thereof varies substantially linearly from the zero magnetic field to the positive magnetic field and the material has properties which are sufficiently suitable for the application to an MR sensor. Nevertheless, in order to obtain a large MR change, a magnetic field having an intensity of about 50 Oes is also required. Thus, such a property is not appropriate for the application to an MR head which is required to be operated at most at about 20 Oes and preferably less.
As a film which can he operated even when a very weak magnetic field is applied, a spin-valve type film in which Fe—Mn as an antiferromagnetic material is attached to a structure of Ni—Fe/Cu/Ni—Fe has been proposed (Journal of Magnetism and Magnetic Materials 93, p. 101, 1991). The operating magnetic field of a magnetoresistive material of this type is actually weak, and a good linearity is observed. However, the MR ratio thereof is as small as about 2%, and the Fe—Mn film has poor corrosion resistance and a low Neel temperature (ordering temperature). Consequently, the properties of such a device disadvantageously exhibit a great temperature dependence.
Furthermore, a spin-valve film having a structure of Ni—Fe/Cu/Co—Pt or the like using a hard magnetic material such as Co—Pt instead of an antiferromagnetic material has also been proposed. In such a case, a parallel magnetization state and an anti-parallel magnetization state are created by rotating the magnetization direction of a soft magnetic layer at a coercivity equal to or less than that of a hard magnetic layer. However, even when such a structure is employed, it is still difficult to improve the properties of the soft magnetic layer. Thus, this structure has not been used practically, either.
Moreover, a structure such as Cu/Ni—Fe/Cu/Ni—Fe/Fe—Mn formed by attaching a low-resistance back layer, made of a metal having a low resistance, to the back of a spin-valve film has also been proposed as a means for increasing the MR ratio of a spin valve film (U.S. Pat. No. 5,422,571). Such a structure is an attempt to increase the MR ratio by lengthening the mean free path of the electrons having a particular spin direction.
A conventional spin-valve type MR device, no matter whether the device is of the type using an antiferromagnetic material or of the type using a hard magnetic layer, had a problem in that the MR ratio thereof is low, even though the magnetic field sensitivity thereof is excellent. Similarly, the MR ratio cannot be satisfactorily increased even when the low-resistance back layer is provided. This is presumably because a small thickness of a spin-valve type MR device is likely to cause the diffusive scattering of electrons on the surface of the device.
Such a phenomenon can be explained in more detail as follows.
A giant magnetoresistance effect originally results from the spin-dependent scattering of electrons at an interface between a magnetic layer and a non-magnetic layer. Thus, in order to increase the possibility of the scattering generation, it is important to lower the possibility of the non-spin-dependent scattering generation and to lengthen the mean free path of electrons. In a spin-valve film, the number of magnetic layers and non-magnetic layers to be stacked is small. Thus, the film thickness of a spin-valve film is generally smaller (e.g., in the range from about 20 nm to about 50 nm) than that of an antiferromagnetic coupling type giant magnetoresistive film. Consequently, the possibility that electrons are scattered on the surface of such a film is high, and the mean free path of electrons is short. This is the principal reason why the MR ratio of a spin-valve film becomes low.
Ordinarily, the surface of a thin film has some unevenness on the order of several tenths of a nm which is substantially on the same order of the wavelength of conduction electrons (i.e., a Fermi wavelength). In such a case, the conduction electrons are subjected to diffusive scattering on the surface of the film. In general, in the case of a diffusive scattering, the spin direction of electrons is not maintained.
SUMMARY OF THE INVENTION
The magnetoresistive device of the present invention includes: at least two magnetic layers stacked via a non-magnetic layer therebetween; and a metal reflective layer of conduction electrons formed so as to be in contact with at least one of outermost two layers of the magnetic layers. the metal reflective layer being in contact with one surface of the outermost magnetic layer which is opposite to the other surface of the outermost magnetic layer in contact with the non-magnetic layer, the metal reflective layer be
Kawawake Yasuhiro
Sakakima Hiroshi
Satomi Mitsuo
LandOfFree
Magnetoresistive device having a highly smooth metal... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Magnetoresistive device having a highly smooth metal..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Magnetoresistive device having a highly smooth metal... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3063602