Dynamic magnetic information storage or retrieval – Head – Hall effect
Patent
1997-04-18
1999-07-13
Cao, Allen T.
Dynamic magnetic information storage or retrieval
Head
Hall effect
G11B 5127
Patent
active
059235047
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a magnetoresistance device having a magnetoresistance effect element for reading the magnetic field intensity of a magnetic recording medium or the like as a signal and, in particular, to a magnetoresistance device, such as a magnetoresistance effect type head, having a magnetoresistance effect element which is capable of reading a small magnetic field change as a greater electrical resistance change signal.
BACKGROUND ART
Recently, there has been the development for increasing the sensitivity of magnetic sensors and increasing the density in magnetic recording and, following this, magnetoresistance effect type magnetic sensors (hereinafter referred to as MR sensors) and magnetoresistance effect type magnetic heads (hereinafter referred to as MR heads) using magnetoresistance change have been actively developed. Both MR sensors and MR heads are designed to read out external magnetic field signals on the basis of the variation in resistance of a reading sensor portion formed of magnetic material. The MR sensors have an advantage that a high sensitivity can be obtained and the MR heads have an advantage that a high output can be obtained upon reading out signals magnetically recorded in high density because the reproduced output does not depend on the relative speed of the sensors or heads to the recording medium.
However, conventional MR sensors which are formed of magnetic materials such as Ni.sub.0.8 FeO.sub.0.2 (Permalloy), NiCo or the like have a small resistance change rate .DELTA.R/R which is about 1 to 3% at maximum, and thus these materials have insufficient sensitivity as the reading MR head materials for ultrahigh density recording of the order of several Giga Bits Per Square Inches or more.
Attention has been recently paid to artificial lattices having the structure in which thin films of metal having a thickness of an atomic diameter order are periodically stacked, because their behavior is different from that of bulk metal. One of such artificial lattices is a magnetic multilayer film having ferromagnetic metal thin films and antiferromagnetic metal thin films alternately deposited on a substrate. Heretofore, magnetic multilayer films of iron-chromium and cobalt-copper types have been known. Among these materials, the iron-chromium (Fe/Cr) type was reported to exhibit a magnetoresistance change which exceeds 40% at an extremely low temperature (4.2 K). However, this artificial lattice magnetic multilayer film is not commercially applicable if it is left as it is because the external magnetic field at which a maximum resistance change occurs (operating magnetic field intensity), is as high as ten to several tens of kilo-oersted. Additionally, there have been proposed artificial lattice magnetic multilayer films of Co/Ag, which require too high operating magnetic field intensity.
Under these circumstances, a new structure which is called a spin valve has been proposed. In this structure, two NiFe layers are formed through a non-magnetic layer, and an FeMn layer is further formed so as to be adjacent to one of the NiFe layers. In this case, since the FeMn layer and the NiFe layer adjacent thereto are directly exchange-coupled to each other, the direction of the magnetic spin of this NiFe layer is fixed in the range of several tens to several hundreds Oe in magnetic field intensity. On the other hand, the direction of the magnetic spin of the other NiFe layer is freely varied by an external magnetic field. As a result, there can be achieved a magnetoresistance change rate (MR ratio) of 2 to 5% in a small magnetic field range which corresponds to the degree of coercive force of the NiFe layer. In addition, the following papers have been published.
a. Physical Review B, 43 (1991) 1297 film thickness (unit: .ANG.) of each layer, also applied hereinafter! is reported to exhibit that its MR ratio sharply rises up to 5.0% at an applied external magnetic field of 10 Oe.
b. Journal of Magnetism and Magnetic Materials, 93 (1991) 101
Si/Ta(50)/NiFe(60)/Cu(
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Araki Satoru
Sato Yuichi
Shinoura Osamu
Cao Allen T.
TDK Corporation
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