Thin film magnetic head

Abstract: There is disclosed a thin film magnetic head which requires less recording current, and is capable of recording and reproducing with a high sensitivity. To achieve this magnetic head, a third yoke (15,21) of a high permeability is bridged across a notched portion of a second yoke (12) between front (10) and back (11) portions of the second yoke constituting part of a magnetic circuit. With this construction, the third yoke serves to extremely reduce a magnetic resistance between the front and back portions of the second yoke, so that the record­ ing current can be smaller, thereby enhancing the recording efficiency.

Description: This invention relates generally to a thin film magnetic head for use in a magnetic recording apparatus and more particularly to a thin film magnetic head which comprises a recording and reproducing head and provides a single common read-write gap. A conventional coil-type magnetic head produces a reproducing output proportional to the running speed of a recording medium. On the other hand, a thin film magnetic head using a magneto-resistive effect produces a constant reproducing output irrespective of a relative speed between the magnetic head and the recording medium, and therefore a high reproducing output is available even under the condition of low relative speed. For this reason, recently, thin film magnetic heads of this type have been extensively used in magnetic recording apparatii. However, a thin film magnetic head of the magneto-resistance effect type has no recording ability, and therefore in order for the magnetic head to have both recording and reproducing functions, it has been necessary that such a head be combined with a coil-type inductive thin film magnetic head. Such a magnetic head is already known, for example, from Japanese Patent Unexamined Publication Nos. 52-12814 and 61-48116. In a conventional thin film magnetic head, a lower magnetic layer and an upper magnetic layer both extend linearly in opposed relationship to each other on a substrate. The lower and upper magnetic layers cooperate with a magnetic gap, formed between these magnetic layers, to provide a magnetic circuit. A coil layer is formed around the magnetic circuit. The upper magnetic layer is divided into two portions, i.e., a front portion and a rear (back) portion, and a magneto-resistive element is provided to bridge the front and rear portions. The operation of this thin film magnetic head will now be described. At the time of recording, recording current flows through the coil layer, so that a recording magnetic field leaks from the magnetic gap to the outside. Recording onto a recording medium is effected by this magnetic field. At the time of reproducing, a signal flux generated from the recording medium flows into the magneto-resistive element from the magnetic gap via the front portion of the upper magnetic layer. The signal is sensed by variations in resistance of the magneto-resistive element. Namely, a drive current is applied to the magneto-resistive element, and the variation in resistance of the magneto-resistive element is converted into a voltage such that the signal can be read. However, in such a conventional thin film magnetic head, a magnetic resistance is large at a dividing portion of the upper magnetic layer which separates its front portion from its rear portion. This results in a problem that the recording medium is quite large. The increase of the recording current requires an increase in the size of a circuit for driving the thin film magnetic head, and therefore is a factor in the failure to provide a compact or small-size construction for a magnetic recording apparatus. Also, the increase of the recording current raises the temperature of the thin film magnetic head, and therefore is a factor in the deterioration of the durabilities of the thin film magnetic head and the magnetic recording medium. United States patent specification No. 3 921 217 describes a thin film magnetic head comprising a first yoke of a soft magnetic material; a second yoke of a soft magnetic material, part of said second yoke being notched to provide a notched portion dividing said second yoke into a front yoke and a back yoke, the front yoke cooperating with the first yoke to provide a read-write gap and the back yoke being magnetically connected to the first yoke; a magneto-resistive element disposed below the notched portion; current supply means for supplying drive current to said magneto-resistive element; and a third yoke of a soft magnetic material bridging the front and back yokes. With the problems of the prior art in mind, it is an object of this invention to provide a thin film magnetic head which needs a small recording current, and is capable of recording and reproducing with high sensitivity. One aspect of the present invention is characterised in that said third yoke does not extend to the read-write gap and bridges the front and back yokes such that the overall magnetic reluctance of the magnetic head is reduced. Another aspect of the present invention is characterised in that the third yoke bridges the front and back yokes such that it connects directly with said front and back yokes and the coercive force of the material of the third yoke is greater than that of the material of the second yoke. Fig. 1 is a schematic perspective view of a thin film magnetic head according to one preferred embodiment of the present invention; Fig. 2 is a cross-sectional view taken along line II-II of Fig. 1; Fig. 3 is a cross-sectional view of a portion of a thin film magnetic head according to a second embodiment of the present invention; and Fig. 4 is a cross-sectional view of a portion of a thin film magnetic head according to a third embodiment of the invention. A thin film magnetic head 100 according to a preferred embodiment of the invention will now be described with reference to the structures shown in Figs. 1 and 2. A first yoke 2 of a soft magnetic material, such as permalloy and Sendust, is formed by a sputtering process on a substrate 1 of a non-magnetic material such as ceramics and glass. A first insulative layer 4 made of an insulative material (i.e., SiO₂) is formed on an upper surface of the first yoke 2, part of the first insulative layer 4 serving as a read-write gap 3. A coil layer 5 and a second insulative layer 6 are formed on the first insulative layer 4 by sputtering process or the like. A magneto resistive element 7, made of a nickel-iron alloy, and electrodes 8 and 9 are formed on the second insulative layer 6. A second yoke 12 divided into two portions, i.e., a front yoke 10 and a back yoke 11, is formed over the magneto resistive element 7 on a third insulative layer 13, the second yoke 12 being made of permalloy, Sendust or the like. A non-magnetic layer 14 is formed on the second yoke 12, and a third yoke 15 of a soft magnetic material is formed to bridge the front and back yoke 10 and 11 of the second yoke 12. Reference numeral 16 denotes a protective layer made of an alumina film. The operation of the thin film magnetic head 100 will now be described. At the time of recording, write current is applied to the coil 5 to generate a recording magnetic field which is fed to the read-write gap 3 via a magnetic circuit constituted by the back yoke 11 of the second yoke 12, the third yoke 15, the front yoke 10 of the second yoke 12 and the first yoke 2, so that the signal is written onto a recording medium. Because of the provision of the third yoke 15, a magnetic reluctance (resistance) produced between the front and back yokes 10 and 11 of the second yoke 12 at the time of recording is very small. Therefore, the recording efficiency of the thin film magnetic head of this embodiment can be improved so as to provide the efficiency of several times higher than that of a conventional thin film magnetic head not provided with such third yoke. At the time of reproducing, a signal flux from the recording medium flows into the magneto resistive element 7 via the front yoke 10. At this time, part of the signal flux also flows into the third yoke 15. However, because of the provision of the third yoke 15, the overall magnetic resistance of the magnetic head is reduced, and the amount of the signal flux flowing into the magnetic head from the recording medium is markedly increased. Therefore, the amount of the magnetic flux flowing into the magneto resistive element 7 is generally equal to that achieved with the conventional magnetic head. Therefore, the composite-type thin film magnetic head of this embodiment has generally the equivalent reproducing sensitivity in comparison with that of the conventional magnetic head. Such effects can also be obtained when the third yoke 15 is so formed as to be in direct contact with the back yoke 11 of the second yoke 12. By forming the second yoke 12 and the third yoke 15 from the same soft magnetic material, the steps of the manufacturing process can be reduced. Fig. 3 is a view similar to Fig. 2, but showing a thin film magnetic head 200 according to a second embodiment of the present invention. In this embodiment, a third yoke 21 is formed in such a manner that it is connected directly to the upper portion of the second yoke 12. The third yoke 21 is made of such a material that the coercive force of the magnetic material for the third yoke 21 is greater than the coercive force of the magnetic material for the second yoke 12. The operation of the thin film magnetic head 200 of the second embodiment will now be described. At the time of recording, as in the first embodiment of Fig. 1, a recording magnetic field is fed to the read-write gap 3 via a magnetic circuit constituted by the back yoke 11 of the second yoke 12, the third yoke 21, the front yoke 10 of the second yoke 12 and the first yoke 2, so that the signal is recorded onto the recording medium. The reproducing in the second embodiment differs from that of the first embodiment. Namely, a signal magnetic flux from the recording medium flows into the magneto resistive element 7 and the third yoke 21 via the front yoke 10. At this time, most of the signal magnetic flux flows into the magneto resistive element 7. The reason for this is that since the third yoke 21 is made of a soft magnetic material having a large coercive force, the third yoke 21 hardly allows a weak magnetic flux to pass during the reproducing. Therefore, the thin film magnetic head of this embodiment has generally the same reproducing sensitivity as the conventional magnetic head. Fig. 4 is a sectional view similar to Fig. 2, but showing a thin film magnetic head 300 according to a third embodiment of the present invention. A third yoke 21 is formed in such a manner that it is extended to the read-write gap 3. In this case, since a recording magnetic field passes through the third yoke 21 and reaches the read-write gap 3, the recording efficiency is further improved. Also, the film thickness of the second yoke 12 can be reduced, and this simplifies the manufacturing process of the thin film magnetic head. In the above three embodiments, although the first yoke 2 is formed on the non-magnetic substrate, the substrate may be made of a magnetic material, in which case this magnetic substrate can be used as the first yoke.

Claims: A thin film magnetic head comprising a first yoke (2) of a soft magnetic material; a second yoke (12) of a soft magnetic material, part of said second yoke (12) being notched to provide a notched portion dividing said second yoke (12) into a front yoke (10) and a back yoke (11), the front yoke (10) cooperating with the first yoke (2) to provide a read-write gap (3) and the back yoke (11) being magnetically connected to the first yoke (2); a magneto-resistive element (7) disposed below the notched portion; current supply means for supplying drive current to said magneto-resistive element (7); a third yoke (15) of a soft magnetic material bridging the front and back yokes (10,11); and a coil (5) disposed around a magnetic circuit constituted by said first yoke (2), said second yoke (12), said third yoke (15) and said read-write gap (3) characterised in that said third yoke (15) does not extend to the read-write gap (3) and it bridges the front and back yokes (10,11) such that the overall magnetic reluctance of the magnetic head is reduced. A thin film magnetic head comprising a first yoke (2) of a soft magnetic material; a second yoke (12) of a soft magnetic material, part of said second yoke (12) being notched to provide a notched portion dividing said second yoke (12) into a front yoke (10) and a back yoke (11), the front yoke (10) cooperating with the first yoke (2) to provide a read-write gap (3) and the back yoke (11) being magnetically connected to the first yoke (2); a magneto-resistive element (7) disposed below the notched portion; current supply means for supplying drive current to said magneto-resistive element (7); a third yoke (21) of a soft magnetic material bridging the front and back yokes (10,11); and a coil (5) disposed around a magnetic circuit constituted by said first yoke (2), said second yoke (12), said third yoke (21) and said read-write gap (3), characterised in that the third yoke (21) bridges the front and back yokes (10,11) such that it connects directly with said front and back yokes (10,11) and the coercive force of the material of the third yoke (21) is greater than that of the material of the second yoke (12). A thin film magnetic head as claimed in claim 2, characterised in that the third yoke (21) bridges the front and back yokes (10,11) such that it extends to the read-write gap (3). A thin film magnetic head as claimed in any preceding claim, characterised in that the first yoke (2) is used as a substrate (1) for the magnetic head.

Inventors: FUKAZAWA TOSHIO, MITANI SATORU, NAGATA YUJI, FUKAZAWA, TOSHIO, MITANI, SATORU, NAGATA, YUJI
Applicants: MATSUSHITA ELECTRIC IND CO LTD, MATSUSHITA ELECTRIC INDUSTRIAL CO., LTD.
Application year: 1990
Main classification: G11B5
IPC codes: G11B5