Electricity: measuring and testing – Magnetic – Magnetometers
Patent
1996-08-05
1997-09-02
Snow, Walter E.
Electricity: measuring and testing
Magnetic
Magnetometers
32420721, 338 32R, G01R 3302, G01B 530, G01D 5245
Patent
active
056636440
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a magnetic signal detection apparatus utilizing a ferromagnetic thin film magneto-resistive element.
BACKGROUND ART
It has been known that a reproduced output and a reproduction sensitivity in converting a small signal magnetic field Hs to a resistance change in a resistive element are enhanced by using a ferromagnetic thin film magneto-resistive element (MR element) as a reproducing head and setting an angle .theta. to approximately 45.degree., where .theta. is an angle made between a direction of magnetization M of the ferromagnetic thin film magneto-resistive element and a current I flowing through the resistive element. An example of prior art in which a biasing magnetic field Hb is applied in a direction of 45.degree. to the direction of the current I is shown in FIG. 8. In FIG. 8, by applying the biasing magnetic field Hb by a biasing magnet 3 in the direction of approximately 45.degree. to the direction of the current I flowing through the thin film magneto-resistive element 2 as shown in a magneto-resistance characteristic of FIG. 9, an operating point at which high linearity and high reproduced output are attained is selected. In FIG. 8, numerals 4 and 5 denote power terminals for supplying the current to the thin film magneto-resistive element 2.
It has also been known to arrange ferro-magnetic thin film magneto-resistive elements at an interval of one half of a magnetic lattice pitch .lambda. and apply a biasing magnetic field. In addition, a method for applying the biasing magnetic field in the direction of 45.degree. has been known as shown in FIG. 10 (JP-B-1-45008). In FIG. 10, numerals 6 and 8 denote power terminals, numeral 7 denotes an output terminal, numeral 9 denotes a biasing magnetic field and numeral 10 denotes a signal magnetic field recording medium.
In any one of the above methods, the biasing magnetic field is applied in the direction of 45.degree. to a longitudinal direction (current direction) of the resistive element. When an MR film formed on a substrate (made of ceramic or glass material) is patterned to form a resistive element (having a film width of several .mu.m.sub..about. several tens .mu.m)., the direction of magnetization M of the resistive element is oriented in the longitudinal direction of the resistive element by a shape effect. In order to orient the magnetization in the direction of 45.degree. to the longitudinal direction by the biasing magnetic field applied in the direction of 45.degree. to the longitudinal direction of the resistive element, it is necessary to apply a large biasing magnetic field in the order of several thousands .sub..about. ten thousands Gausses because a shape energy possessed by the resistive element is large. When a relatively small biasing magnetic field (several hundreds Gausses) is applied, the magnetization of the resistive element is oriented to a direction smaller than 45.degree.. Because of those phenomena, the following problems arise.
(1) Because the magnetization of the resistive element is bound by the large biasing magnetic field or because the direction of magnetization is smaller than 45.degree., a detection output of a small leakage magnetic field of a magnetic material bearing a magnetic signal to be detected is small, a signal to noise ratio is small, a distortion increases and the processing by a signal processing circuit is difficult to attain. Recently, the compactness of the apparatus, the enhancement of the control accuracy and the fine magnetic signal for high fidelity reproduction are required and hence the leakage magnetic field to be detected is becoming more and more weak.
(2) It is necessary to bring the detection element as closely to the magnetic material bearing the magnetic signal as possible to detect in a large area of the signal magnetic field to be detected in order to attain a large output. In order to detect a relative linear displacement or rotational displacement between the magnetic material to be detected and the detection element by a unifor
Mitani Satoru
Shimamura Hiroshi
Matsushita Electric - Industrial Co., Ltd.
Snow Walter E.
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