日本金属学会誌

J. Japan Inst. Metals, Vol. 56, No. 7 (1992),
pp. 849-853

Effects of Induced- and Shape-Magnetic Anisotropy on Magnetoresistive Response Curve of Permalloy Thin Film Sensor

Hitoshi Nakamura1 and Masahiro Kitada1

1Central Research Laboratory, Hitachi, Ltd., Kokubunji Tokyo

Abstract:

The purpose of this work is to establish the effect of induced and shape magnetic anisotropy on the magnetoresistive response curve (MRRC) of permalloy thin film sensors. The films were deposited by electron beam system, and the sensors were prepared using photolithography. The dimensions of the sensor were 300 μm long, 20 μm wide and 0.05 μm thick. The direction of the induced anisotropy was tilted through θ=0°~90° to shape anisotropy (along sensor's length). The MRRC was measured under 50 Hz AC field (H=8 kA/m) applied in the sensor's width. The results are as follows. Discontinuous MRRC with the Barkhausen noise was obtained in the sensors with θ≥qq10° and the maximum noise was attained at θ=90°. However, continuous MRRC without noise was obtained in the sensor with θ=0°~5°. The bitter figure, after the AC erasure along sensor's width, showed a single domain at θ=0° and hence revealing clear domain structure with increasing θ. Domain wall migration caused by the DC magnetic field was observed in the sensor with θ≥qq10°. From these facts it might be said that induced anisotropy contributes to nucleation of the reversed domains which nucleate easily as θ increases. The Barkhausen noise is due to the abrupt expansion of reversed domain. However, the θ dependence of the effective anisotropy direction, α, calculated by a coherent rotation model agrees fairly well with that of the additional AC field direction to the sensor's width direction, Δφ0, which minimizes the Barkhausen noise. This result strongly suggests that the effective anisotropy experimentally obtained is in the direction of Δφ0 from the sensor's length direction, and that the continuous parts of MRRC are due to the coherent rotation based on the effective anisotropy. The maximum value of Δφ0=3° corresponds to θ=40°~50°. Thus, the effective anisotropy might be attributable to the shape anisotropy.


(Received 1991/11/11)

Keywords:

induced-magnetic anisotropy, shape-magnetic anisotropy, magnetoresistive response curve, Barkhausen noise, domain structure, reversed domain, effective anisotropy


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