Dynamic magnetic information storage or retrieval – Head – Magnetoresistive reproducing head
Reexamination Certificate
1999-09-29
2001-12-11
Davis, David (Department: 2652)
Dynamic magnetic information storage or retrieval
Head
Magnetoresistive reproducing head
Reexamination Certificate
active
06330135
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a magneto-resistance effect element that has high magnetic sensitivity and is effective as a magnetic sensor for detecting weak magnetic fields.
2. Description of the Prior Art
A compact magnetic sensor capable of detecting weak magnetic fields is indispensable for the realization of the next-generation of high-density magnetic recording devices. Heads using the magneto-resistance (MR) effect of a metal or metal alloy (MR heads) are recently being used in place of the induction-type read heads in wide use up to now. This has enabled reading of high-density magnetically recorded information difficulty to read with an induction-type head.
The metals or alloys used in such heads obviously cannot be used for reading still higher density magnetic recording, however, because the magnitude of their magneto-resistance effects measured in terms of resistance change rate is only about 1%.
Colossal magnetoresistance oxides, which have recently been attracting attention for their ability to provide large magneto-resistance effect, have therefore come under study for use in read heads. As reported at p2041 of
Physical Review Letters
, vol. 77, for example, the large magneto-resistance effect in weak magnetic field (10% or greater) observed at the grain boundary of a polycrystal La
1−x
Sr
x
MnO
3
, a perovskite exhibiting ferromagnetism, is highly promising for application to high-sensitivity magnetic sensors. A report appearing at p8357 of
Physical Review B
, vol. 54 describes an attempt to utilize the magneto-resistance effect of this perovskite to the utmost by fabricating a so-called tunnel junction element comprised of an insulator film sandwiched between two ferromagnetic films. A magneto-resistance effect of greater than 80% is said to have been obtained.
However, this tunnel junction element has the major drawback of being difficult to fabricate. The reason for this is that the insulator film sandwiched between the ferromagnetic films of the tunnel junction should best be no greater than several nanometers (nm). Fabrication of such a thin insulation film without current shorting is extremely difficult. Moreover, the complexity of the element structure complicates the fabrication process and necessitates sophisticated process optimization. These problems can be assumed to become more pronounced with decreasing element size. Application of the tunnel junction element to a head for reading high-density magnetically recorded information is therefore thought to be quite difficult.
On the other hand, recent breakthroughs in thin oxide thin film growth technology have made it possible to obtain good quality epitaxially grown thin films of oxide that exhibit perfect lattice matching with the substrate. A report appearing at p1540 of
Science
, vol. 266, for example, points out that even if an atomic-scale level difference (step) should be present on the substrate surface owing to the crystallographic structure (crystal structure) of the substrate, the thin film will continue to grow while maintaining the stepped condition. Depending on the crystal structure of the grown thin film and the film growth conditions at this time, portions other than that directly above the step are perfectly monocrystalline while only the step portion is formed thereon with a film whose atomic arrangement exhibits disorderly periodicity in directions parallel to the thin film surface, namely, a film having a so-called antiphased domain boundary. The presence of an antiphased domain boundary is, however, undesirable in the field of compound semiconductors because it causes carrier scattering and boundary surface levels.
An object of this invention is to provide a magneto-resistance effect element that has a high magnetic sensitivity of not less than 50%, is easy to fabricate, and can be effectively used as a magnetic sensor for detecting weak magnetic fields.
SUMMARY OF THE INVENTION
For achieving this object, this invention provides a magneto-resistance effect element comprising an oxide substrate having on its surface steps of atomic layer level and on the substrate an epitaxially grown ferromagnetic oxide thin film, the thin film formed on the atomic layer level steps having an antiphased domain boundary.
In one aspect of the invention, the ferromagnetic oxide thin film is one represented by the formula RE
3−X
AE
X
Mn
2
O
7
, where RE is at least one rare earth element selected from the group consisting of Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu, AE is at least one alkaline earth metal selected from the group consisting of Mg, Ca, Sr and Ba, X is 0-3, and the oxide substrate is a <100> substrate of SrTiO
3
.
In another aspect of the invention, the ferromagnetic oxide thin film is one represented by the formula AE
2−X
RE
X
FeMO
6
, where RE is at least one rare earth element selected from the group consisting of Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu, AE is at least one alkaline earth metal selected from the group consisting of Mg, Ca, Sr and Ba, M is Mo or Re, X is 0-2, and the oxide substrate is a <111> substrate of SrTiO
3
.
When a ferromagnetic oxide thin film is epitaxially grown on an oxide substrate having atomic layer level steps on its surface in the foregoing manner, an antiphased domain boundary is formed in the thin film directly above the substrate steps and a large magneto-resistance effect is observed when the electrical resistance is measured in the direction perpendicular to the antiphased domain boundary.
When a <100> substrate of SrTiO
3
is used as the oxide substrate, the effect of the invention is maximized by conducting a chemical surface treatment that defines the atomic layer at the outermost surface of the substrate as TiO
2
. When a <111> substrate of SrTiO
3
is used as the oxide substrate, good effect is obtained when the formation of the film of AE
2−X
RE
X
FeMO
6
is preceded by forming as a buffer a SrFeO
3
thin film ending with a FeO
2
surface.
The above and other features of the present invention will become apparent from the following description made with reference to the drawings.
REFERENCES:
patent: 4586957 (1986-05-01), Masumoto et al.
patent: 4642145 (1987-02-01), Masumoto et al.
patent: 64-50575 (1989-02-01), None
patent: 1-241876 (1989-09-01), None
Q. LI, et al., Proceedings of the International Magnetics Conference, p. AC-01 “Giant Magnetoresistance in EPITAXIAL Nd-Sr-Mn-O Films and other Oxides,”April 18, 1995.
H.Y. Hwang, et al., Database Inspec. 'Online!, Institute of Electrical Engineers, vol. 77, An 5373364, “Spin-Polarized Intergrain Tunneling In La/sub 2/3/Sr/sub 1/3MnO/sub 3,” Sep. 2, 1996 (Abstract Only).
M. Kawasaki, et al., Database Inspec. 'Online!, Institute of Electrical Engineers, vol. 266, An 4873634, “Atomic Control of the SrTIO3Crystal Surface,” Dec. 2, 1994 (Abstract Only)
R. Shreekala, et al., Database Inspec. 'Online!, Institute of Electrical Engineers, vol. 71, An 5644836, “Effect of Crystallinity on the Magnetoresistance in Perovskite manganese oxide Thin Films,”Jul. 14, 1997 (Abstract Only).
M. Rajeswari, et al., Database Inspec. 'Online!, Institute of Electrical Engineers, vol. 73 AN 6076749 “Correlation Between Magnetic Homogeneity, Oxygen Content, and Electrical and Magnetic Properties of Perovskite Manganite Thin Films,” Nov. 1998 (Abstract Only).
Izumi Makoto
Kawasaki Masashi
Kobayashi Kei-Ichiro
Konishi Yoshinori
Manako Takashi
Davis David
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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