Dynamic magnetic information storage or retrieval – Head – Core
Reexamination Certificate
2000-03-07
2001-02-27
Korzuch, William R. (Department: 2754)
Dynamic magnetic information storage or retrieval
Head
Core
Reexamination Certificate
active
06195233
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a thin-film magnetic head for use in a magnetic disk apparatus, a VTR, etc., and a magnetic write/read apparatus equipped with this magnetic head, and more particularly, to a very small thin-film magnetic head which has low recording magnetomotive force necessary for magnetizing a magnetic recording medium, has a fewer number of recording coil turns and has a very narrow track width, and a magnetic write/read apparatus equipped with this magnetic head.
2. Description of the Related Art
For an inductive magnetic head which has been conventionally popular, when used both for writing and reading, it is in principle advantageous to increase the number of coil turns because this provides a larger reading output. With such a magnetic head used exclusively for information writing, however, the number of coil turns can be reduced as long as the magnetomotive force required for writing is satisfied. The inductive magnetic head for exclusive use in information writing, therefore, has a simpler structure than the aforementioned inductive magnetic head designed both for writing and reading, thus facilitating the head fabrication process and improving the production yield. The magnetic head for writing only has a further advantage in easier miniaturization of the magnetic core portion and easily ensuring the high efficiency of the head.
It is a magnetic head with a single-turn coil which has the simplest structure and is attractive. It is known that the recording current needed to magnetize a magnetic recording medium using a single-turn magnetic head fabricated by the prior art design technology is around 1 A (Ampere), namely, 0.7 to 0.8 A or 1.5 A. (See E. P. Valsyn and L. F. Shew, “Performance of Single-Turn Film Heads,” IEEE Trans. MAG-9, No. 3, September 1973, and W. Chynoweth, “Small Thin-film Transducers Point to Fast, Dense Storage Systems, Electronics, July 25, pp. 122-127, 1974.)
This means that the magnetomotive force of the conventional single-turn coil magnetic head does not differ from that of the conventional inductive magnetic head designed for writing and reading (several dozens of turns), which is about 1 A·T (Ampere·Turn).
Since the conventional single-turn head or few-turns head requires a recording current larger by a factor of several tens than that of the writing/reading head, the burden on the driver circuit to supply the recording current is very heavy. What is more, because of the large current, the heat generated by the coil portion will deteriorate the characteristic and reliability of the head. To cope with never stopping improvement of the density of magnetic recording apparatuses, there will be expected demands for further miniaturization of the magnetic core and further reduction of the number of coil turns. This therefore requires some design scheme for a low-magnetomotive force magnetic head, which can magnetize a magnetic recording medium with a low magnetomotive force, preferably of several dozens of milliamperes·turns (mA·T), similar to the writing current needed by the conventional inductive write/read magnetic head.
Further, since the thickness of the magnetic pole in the plane facing the recording medium for the conventional inductive magnetic head is on the order of several micrometers (&mgr;m), the dimensional tolerance of machining for the pole track width has been considered to be limited to around ±0.5 &mgr;m as long as the state-of-the-art film etching process is used, and it is very difficult to provide a narrow track width of 1 &mgr;m or below. A solution to this shortcoming has been craved so far.
SUMMARY OF THE INVENTION
It is therefore a primary object of the present invention to provide a very small, single-turn or few-turns thin-film magnetic head, which needs considerably lower magnetomotive force for recording than the conventional heads, is excellent in processing precision, and will ensure recording with a very narrow track width of several &mgr;m or narrower, particularly, 1 &mgr;m or narrower.
It is another object of this invention to provide a magnetic write/read apparatus which will exhibit excellent writing and reading characteristics and a high reading S/N ratio.
To achieve the above objects, according to one aspect of this invention, there is provided a thin-film magnetic head comprising a ring-shaped magnetic core and a coil surrounded by the magnetic core, given that an inner circumferential length of the magnetic core surrounding the coil is Lc, a magnetic gap length is g, a magnetic gap depth is D, an average magnetic flux density (unit: T (tesla)) is Bav and an effective magnetic permeability of the magnetic core is &mgr;, Lc, g and D being determined in such a manner that a magnetomotive force I needed for recording, expressed by a following equation (1), becomes 0.001 A·T to 0.1 A·T (Ampere·Turn):
I
=
2
π
DBav
μLog
{
[
(
Lc
+
g
)
+
2
π
D
]
/
(
Lc
+
g
)
}
(
1
)
wherein Log is a natural logarithm, and variables in the equation (1) are expressed in SI units.
According to another aspect of this invention, there is provided a perpendicular thin-film magnetic head comprising a magnetic core having a main magnetic pole and a return path of a high magnetic permeability to be magnetically coupled to the main magnetic pole, and a coil surrounded by the magnetic core, for accomplishing writing and reading when in use with a perpendicular double-layered magnetic recording medium having a highly permeable layer and a perpendicular recording layer laminated on a substrate in a named order, given that an inner circumferential length of the magnetic core surrounding the coil is Lc, a distance from the medium opposing face of the perpendicular thin-film magnetic head to a recording-layer side face of the highly permeable layer of the recording medium is S, an interval between the main magnetic pole and the return path at a position of the medium opposing face is Lb, a film thickness in a vicinity of the medium opposing face of the main magnetic pole is Tm, an average value of the density of a magnetic flux (unit: T (tesla)) generated toward the highly permeable layer from a distal end portion of the main magnetic pole, needed for sufficiently magnetizing the perpendicular recording layer, is Bav and an effective magnetic permeability of the magnetic core is &mgr;, Lc, S, Lb and Tm being determined in such a manner that a magnetomotive force I needed for recording, expressed by a following equation (2), becomes 0.001 A·T to:
I
=
2
π
TmBav
μLog
{
(
L
+
2
π
Tm
)
/
L
}
(
2
)
wherein Log is a natural logarithm, L=Lc+2S+Lb, and variables in the equation (2) are expressed in SI and variables in the equation (2) are expressed in SI units.
According to a further aspect of this invention, there is provided a magnetic writing/reading apparatus equipped with a recording magnetic head comprising a ring-shaped magnetic core and a coil surrounded by the magnetic core, and a magnetic recording medium on which recording is done by the recording magnetic head, given that an inner circumferential length of the magnetic core surrounding the coil of the recording magnetic head is Lc, a magnetic gap length is g, a magnetic gap depth is D, an average magnetic flux density (unit: T (tesla)) is Bav and an effective magnetic permeability of the magnetic core is &mgr;, Lc, g and D are determined in such a manner that a magnetomotive force I needed for recording, expressed by a following equation (1), becomes 0.001 A·T to 0.1 A·T (Ampere·Turn), and a magnetic field Hx in a magnetic-head running direction of the magnetic recording medium immediately below a center portion of a magnetic gap of the recording magnetic head being expressed by a following equation (3) and the magnetic field Hx and coercive force Hc of the magnetic recording medium having a relation of Hx>Hc:
I
=
2
π
DBav
μLog
{
[
(
Lc
+
g
)
+
2
π
D
]
/
(
Lc
+
g
)
}
(
1
)
where Log is a n
Akiyama Junichi
Yoda Hiroaki
Kabushiki Kaisha Toshiba
Korzuch William R.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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