Dynamic magnetic information storage or retrieval – Head – Hall effect
Reexamination Certificate
2002-02-19
2004-09-14
Evans, Jefferson (Department: 2652)
Dynamic magnetic information storage or retrieval
Head
Hall effect
Reexamination Certificate
active
06791792
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a magnetic sensor for sensing magnetic fields and a magnetic reading head for reproducing information recorded onto a magnetic disc, and particularly to a magnetic sensor and a magnetic reading head, which offer excellent reproduction and resolution.
2. Descriptions of the Related Arts
Magnetic recording/reproduction apparatuses have made remarkable improvements in their recording densities. Magnetic recording/reproduction heads thereof have been required to possess high performance in terms of both recording and reproduction characteristics. Concerning reproduction devices, improvements of three technical points have been demanded: (1) an improvement in a high sensitivity technique, (2) an improvement in a narrowing technique of a track width, and (3) an improvement in a narrowing technique of a reproduction gap. As to the point (1), the high sensitivity of the reproduction device has been advanced by improving a MR head utilizing a magnetoresistive effect. In a low recording density of several Gb/in
2
, the MR head converted a magnetic signal recorded on a recording medium to an electric signal by use of an anisotropic magnetoresistive effect (AMR), and when the recording density became high so as to exceed several Gb/in
2
, the MR head coped with this high recording density by use of a giant magnetoresistive effect (GMR) capable of producing higher sensitivity. With regard to the magnetic head utilizing the GMR, a structure called a spin valve is described, for example, in Japanese Patent Laid-Open No. 4(1992)-358310. The spin valve consists of a fixed layer made of a magnetic substance in which magnetization is fixed in a specified direction by an antiferromagnetic layer, and a free layer made of a magnetic film laminated on the fixed layer with a nonmagnetic thin film interposed therebetween. The spin-valve changes its electric resistance in response to a relative angle between the magnetization directions of the fixed and free layers.
However, with the recent development as to the high sensitivity of the reproduction device, a novel reproduction system for coping with further high sensitivity has been required. As likely reproduction systems, an advanced GMR effect called a specular-GMR or a NOL-GMR, in which a high spin polarization material or an oxide layer is sandwiched between interfaces of a GMR structure, and an increase of outputs is aimed at by a multi-reflective effect of spins of electrons; a GMR (CPP-GMR) which adopts a system for allowing a detection current to flow in a direction perpendicular to a film plane; and a tunneling magnetoresistive effect (magnetic tunnel junction effect) (TMR) are nowadays prospective.
These effects apply magnetoresistivity change phenomenon in a magnetoelectric effect. Herein, a Hall effect is also a kind of magnetoelectric effects, and a phenomenon in which when a magnetic field is applied in a direction perpendicular to a current flowing through a substance, a voltage is generated in a direction perpendicular to both of the current and the magnetic field. The Hall effect has been recognized for a long time, in which a carrier density and a scattering constant of electrons participate. The Hall effect has been applied to magnetic field measurements by use of a Hall generator formed of a semiconductor as that substance. The attempts to apply the Hall effect to the magnetic reading head are disclosed in Japanese Patent Laid-Open No. 2(1990)-308409 and the like. In this case, similarly to the Hall generator formed of a semiconductor, proposed are a system in which four electrode terminals as current terminals and voltage terminals are provided in a film plane and a signal magnetic field perpendicular to the film plane is measured; and a differential mechanism for sensing an inversion portion of a magnetic field by using a structure in which the two films are superposed thus forming an element having a thickness smaller than a bit interval of a magnetic recording. In Japanese Patent Laid-Open No. 9(1997)-289344, a fundamental principle for an in-plane magnetic recording is proposed as the magnetic field sensor utilizing an anomalous Hall effect of 3d-metal.
In a case where a structure of a reproduction device in future is considered, when the recording device adopts the conventional in-plane magnetic recording system, it is difficult for the recording device to produce a sufficient recording magnetic field, and the CPP-GMR and the TMR that are magnetic resistance sensors showing a high sensitivity are magnetic field sensors utilizing a structure for allowing a sensing current to flow perpendicularly to the film plane. Accordingly, it is anticipated that the reproduction device will switch over a structure of the CPP type through which a sensing current flows. However, when such a structure is adopted and a device area of the magnetoresistive sensor film is made small, a volume of a thickness of the magnetic film constituting the sensor film becomes small with the microfabrication and the thinness of the magnetoresistive sensor device, and its magnetization fluctuates by thermal fluctuation. Accordingly, a new problem that a predetermined magnetization ratio cannot be secured occurs.
When the Hall effect is utilized, materials of the current semiconductor Hall generator fundamentally show a linear output voltage for a magnetic field. Accordingly, the Hall generator demonstrates an advantage in measuring the magnetic field in a wide range. However, the Hall generator shows a small output for a micro magnetic field. Moreover, since these semiconductor materials are generally nonmagnetic (antimagnetic), it is difficult to concentrate a stray magnetic field from a recording medium on a sensing portion in the case where the magnetic field sensor is constituted by the Hall generator, and to enhance sensitivity. When the high-sensitive magnetic field sensor is fabricated with such a film, a structure capable of concentrating the magnetic filed on the sensing portion must be adopted, and a sensor film showing a large output for the magnetic field is necessary.
SUMMARY OF THE INVENTION
In consideration for the problems of the magnetic field sensor utilizing the Hall effect, an object of the present invention is to provide a magnetic field sensor having a structure which can be applied to magnetic reading heads and magnetic random access memories (MRAM).
To achieve the foregoing object, in the present invention, the magnetic field sensor is constituted by use of a material showing an anomalous Hall effect (magnetically induced Hall effect). This magnetic field sensor is applied with a magnetic field to detect a signal containing anomalous Hall effect components.
FIG. 1
shows a relation between a magnetic field B of a material showing the Hall effect and a material showing the anomalous Hall effect and a Hall voltage thereof. The conventional magnetic field sensor, particularly the Hall generator, which utilize the Hall effect (normal Hall effect), use a nonmagnetic semiconductor such as InSb. As apparent from
FIG. 1
, an output (Hall resistance) &rgr;
H
at this time is expressed as follows,
&rgr;
H
=R
H
B
where B is an applied magnetic field (magnetic flux density), and R
H
is a Hall constant. The output &rgr;
H
is a value in proportion to the applied magnetic field B, and the Hall constant R
H
is in inverse proportion to a carrier density of a substance forming the sensor. On the contrary, when a material showing the Hall effect is a magnetic substance, the output (Hall resistance) &rgr;
H
is expressed as follows,
&rgr;
H
=R
H
B+R
S
M
where B is an applied magnetic field (magnetic flux density), M is magnetization of the magnetic substance, and R
S
is an anomalous Hall constant. The output &rgr;
H
contains components in proportion to the magnetization M. Moreover, the anomalous Hall constant R
S
has a value anticipated by fluctuations of temperature and magnetization. Accordingly, in the magnetic substance having a soft magne
Antonelli Terry Stout & Kraus LLP
Evans Jefferson
Hitachi , Ltd.
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