Stock material or miscellaneous articles – Composite – Of inorganic material
Reexamination Certificate
1998-08-27
2001-02-06
Kiliman, Leszek (Department: 1773)
Stock material or miscellaneous articles
Composite
Of inorganic material
C428S690000, C428S690000, C428S690000, C428S900000, C360S112000, C360S114050, C360S125330, C148S304000, C148S403000
Reexamination Certificate
active
06183889
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a magneto-impedance element comprising a glassy alloy which is composed of at least one base metal selected from the group consisting of Fe, Co and Ni; at least one additional metal selected from the group consisting of Zr, Nb, Ta, Hf, Mo, Ti and V; and B.
The present invention also relates to a magnetic head having the magneto-impedance element.
The present invention further relates to a thin film magnetic head comprising an upper core and a lower core which have the magneto-impedance element.
The present invention also relates to an azimuth sensor having the magneto-impedance element.
The present invention further relates to an atutocanceler having a magnetic sensor composed of the magneto-impedance element.
2. Description of the Related Art
With rapid progress in development of information devices, gauging devices, and control devices, magneto-detective elements, which have a smaller size, higher sensitivity and more rapid response than conventional magnetic-flux type elements, have been required. Elements having a magneto-impedance effect, i.e., magneto-impedance elements (hereinafter referred to as MI elements) have attracted attention.
The magneto-impedance effect indicates a phenomenon causing a change in impedance in, for example, a closed circuit as shown in FIG.
5
. When an alternating current Iac having a MHz band is applied to a wire or ribbon magnetic material Mi through an electrical power source Eac while an external magnetic field Hex of several gausses is applied in the longitudinal direction of the magnetic material Mi, a voltage Emi by an impedance inherent in the magnetic material occurs between two ends of the magnetic material Mi, and its amplitude varies within a range of several tens percent in response to the intensity of the external magnetic field Hex. Since the MI element is sensitive to an external magnetic field in the longitudinal direction of the element, the sensitivity for detecting a magnetic field does not deteriorate when the length of the sensor head is 1 mm or less. The MI element enables fabrication of a very weak magnetic field sensor having a high resolution of 10
−5
Oe or more and excitation at several MHz or more, hence a high-frequency magnetic field of 200 MHz to 300 MHz can be used as a carrier for frequency modulation, and thus the cutoff frequency of the magnetic field sensor can be easily set to 10 MHz or more. Accordingly, the MI element is expected to be used in novel ultra-compact magnetic heads and sensors for very weak magnetic fields.
Known materials having MI effects include, for example, (1) amorphous ribbons of Fe—Si—B type alloys, e.g. Fe
78
Si
9
B
13
, and (2) amorphous wires of Fe—Co—Si—B system alloys, e.g. (Fe
6
Co
94
)
72.5
Si
12.5
B
15
(Kaneo Mouri et al., “Magneto-Impedance (MI) Elements”, Papers of Technical Meeting on Magnetics, MAG-94 (1994), Vol. 1, No. 75-84, pp. 27-36, IEE JAPAN).
The Fe—Si—B system and Fe—Co—Si—B system alloys have problems when they are used as MI elements. As shown in
FIG. 6
, when an output voltage Emi (mV) to a positive or negative magnetic field is measured, the Fe—Si—B system alloy i has low sensitivity for detecting the magnetic field, and thus a high amplitude of about 100 times is required. The element, therefore, cannot be used as a magnetic field sensor with a high sensitivity because of noise generation. On the other hand, although the Fe—Co—Si—B system alloy ii has a sufficiently high sensitivity, as shown in
FIG. 6
, it has a steep increase in the sensitivity within a range from −2 Oe to +2 Oe. As a result, it cannot be used as a sensing element for a very weak magnetic field due to non-quantitative measurement within the range. Although it can be used in magnetic field regions of 2 Oe or more as the absolute value, a coil must be provided to apply a considerable amount of current which is required for such a large bias magnetic field.
Recently, further miniaturization and further improvement in recording density have been required in magnetic recording units, such as hard disk drives as external memory units, digital audio tape recorders, and digital video tape recorders. Development of high performance magnetic heads is essential for such requirements, and magnetic reproduction heads using magnetoresistive elements (hereinafter referred to as MR elements) have been developed.
Since a magnetic head having a MR element does not have a dependence of a relative velocity to the recording medium, it is suitable for reading recorded signals at a low relative velocity. It has a low sensitivity to output signals because of a low change rate in response to a change in the recorded magnetization on the recording medium. Accordingly, it will be difficult to satisfy future demands for high-density recording.
Under the above-mentioned circumstances, MI elements have recently attracted attention. As described above, conventional MR elements have a magneto-detective sensitivity of about 0.1 Oe, whereas the MI elements having magneto-impedance effects can detect a magnetization of 10
−5
Oe and are expected to be applied to high-sensitivity magnetic heads.
A typical conventional magnetic sensor of a magnetic head using the MI element will now be described with reference to the drawings. In
FIGS. 28A and 28B
, a magnetic head
201
has a pair of cores
202
a
and
202
b
composed of ferrite as a ferromagnetic oxide, and a MI element
205
as a magnetic material which is bonded to the cores
202
a
and
202
b
with a bonding glass
203
interposed therebetween. The MI element
205
is magnetically coupled with the cores
202
a
and
202
b.
That is, the ends
205
a
and
205
b
in the longitudinal direction of the MI element
205
are bonded to the magnetic circuit connecting faces
203
a
and
203
b
of the cores
202
a
and
202
b,
respectively. An insulating layer is formed on the magnetic circuit connecting faces
203
a
and
203
b.
The cores
202
a
and
202
b
and the MI element
205
thereby form a closed magnetic circuit.
The bonding glass
203
is composed of a nonmagnetic material, prevents direct magnetic coupling between the paired cores
202
a
and
202
b,
and is bonded to the lower faces of the cores
202
a
and
202
b.
A magnetic gap G is provided between the cores
202
a
and
202
b.
A regulating groove
204
is provided on the magnetic gap G for regulating the track width of the magnetic gap G, and filled with glass which is a nonmagnetic material. Conductive films composed of Cu, Au, or the like is deposited to form terminals
206
a
and
206
b
on the two ends of the MI element
205
in the longitudinal direction. The terminals
206
a
and
206
b
are each connected to a lead
207
for extracting output signals and a lead (not shown in the drawings) for applying an alternating current.
The magnetic head
201
operates as follows. An external magnetic field by the recorded magnetization on a recording medium not shown in the drawing invades the cores
202
a
and
202
b
through the magnetic gap G and is applied to the MI element
205
. An alternating current having a MHz band has been previously applied to the MI element
205
to generate a voltage between both ends of the MI element
205
by the impedance inherent in the MI element. The amplitude of the voltage varies within a range of several tens percent in response to the intensity of the external magnetic field and is extracted as output signals through the lead
207
.
The magnetic head
201
using the MI element
205
has a significantly high change in the extracted voltage for a very weak external magnetic field of several gausses which is applied to the MI element
205
from the recording medium, hence the magnetic head
201
can have high sensitivity. Further, such high sensitivity permits reduction in the effective cross-sectional area of the magnetic flux in the magnetic circuit, and thus reduction in the size of the cores
202
a
and
202
b,
resulting in miniaturization of the magnetic head
Inoue Akihisa
Koshiba Hisato
Makino Akihoro
Mizushima Takao
Sasagawa Shinichi
Alps Electric Co. ,Ltd.
Brinks Hofer Gilson & Lione
Kiliman Leszek
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