Magnetic head device

Abstract: A magnetic head device of thin-film type having superior recording and reproducing character­ istics. The magnetic head device has a non-magnetic substrate (11) and lower (12) and upper (23) magnetic layers formed on the substrate. At least one of the magnetic layers (23) has a double-layered structure composed of two soft magnetic layers. One (20) of these soft magnetic layers, which is disposed at the inner side of the magnetic circuit, has a coercive force smaller than that of the other (21) soft magnetic layer. The soft magnetic layer having the greater coercive force, at least at a portion thereof contactable with the recording medium, has a greater width (T1) than the soft magnetic layer of the smaller coercive force as viewed in the direction of the track.

Description: The present invention relates to a magnetic head device and, more particularly, to a magnetic head device of thin-film type. In general, a known magnetic head device of a thin film type has a lower magnetic layer (yoke) made of a soft magnetic material, a gap made of a non-magnetic material and an upper magnetic layer (yoke) which are laminated in the above-mentioned order on a substrate made of a non-magnetic material, so as to form a ring-like magnetic circuit. At the same time, a coil is arranged to wind around this magnetic circuit. When the magnetic head device is used for recording, a signal current is supplied to the coil so that a magnetic field is generated at the gap in accordance with the signal current, so that the signals are magnetically recorded on a recording medium by the magnetic field. Conversely, when the magnetic head device is used for reproducing, a signal magnetic field introduced through the gap is detected by the coil. In the conventional thin-film magnetic head device of winding type, the same magnetic structure is driven both in recording and in reproduction. This means that the track width is the same for both the recording and reproducing phases, so that recording and reproducing performance is impaired for the following reasons. In general, a magnetic head device inevitably exhibits an off-track due to a running offset during running of the recording medium. Representing the track width of the thin-film magnetic head by T and the amount of running offset of the recording medium by ±a, the deviation of the track between the recording phase and the reproducing phase is 2a at its maximum. In such a case, the effective reproduction track width is reduced to (T - 2a), so that reproduction output is undesirably decreased. United States patent specification No. US 3 867 368 discloses a magnetic head device comprising a substrate, a lower yoke formed on said substrate, an upper yoke which forms a magnetic gap at an end thereof adjacent a surface of said lower yoke for making a sliding contact with a recording medium, a conductive coil which winds around a magnetic circuit formed by said lower and upper yokes, wherein the upper yoke forms a coupling magnetically at its other end with the lower yoke and at least one of said lower and upper yokes has a double-layered soft magnetic structure comprising two soft magnetic layers having different levels of coercive force, such that one of the soft magnetic layers which is located on an inner side of said magnetic circuit has a smaller coercive force than that of the other soft magnetic layer and the width of the soft magnetic layer having the greater coercive force, at least at a portion thereof for contacting with a recording medium, is greater than the width of the soft magnetic layer having the smaller coercive force when viewed from a side for making contact with a recording medium. In this construction of a magnetic head device, a magnetic yoke has a double-layered structure but said layers are separated by a non-magnetic layer which acts to magnetostatically decouple said magnetic layers, which have different coercive forces, since it is imperative that the magnetisation of the magnetic layer with the smaller coercive force is not influenced by the magnetisation of the magnetic layer having the larger coercive force. Applicant's own European application No. 90 308 446.5 discloses a magnetic head device comprising a substrate, a lower yoke formed on said substrate, an upper yoke which forms a magnetic gap at an end thereof adjacent a surface of said lower yoke for making a sliding contact with a recording medium and a magnetic coupling at its other end, and a conductive coil which winds around a magnetic circuit formed by said lower and upper yokes, and said upper yoke has a double-layered soft magnetic structure comprising two soft magnetic layers having different levels of coercive force, such that one of the soft magnetic layers which is located on an inner side of said magnetic circuit has a smaller coercive force than that of the other soft magnetic layer. This application forms part of the state of the art pursuant to Articles 54(3) and (4) EPC since is was filed prior to the date of filing of the present application but published subsequent to said date of filing. The magnetic head device of this disclosure is concerned with improving the efficiency of reproduction and recording from/onto a recording medium but does not concern the problem of offtracking. An object of the present invention is to provide a magnetic head device having superior recording and reproducing performance, thereby overcoming the above-described problems of the prior art. To this end, the present invention is characterised over US 3 867 368 in that the layer with the smaller coercive force of the at least one of said lower and upper yokes is formed directly on the other layer having the higher coercive force. The arrangement described above makes it possible to employ different track widths during recording and reproduction, so that the thin-film magnetic head device can maintain an on-track condition regardless of any running offset during recording and reproduction, whereby recording and reproduction are performed stably without causing any reduction in the reproduction output. The features of the invention will be more readily understood from the following description of preferred embodiments, by way of example, with reference to the drawings, of which: Fig. 1 is a schematic perspective view of a first embodiment of a magnetic head device of the present invention; Fig. 2 is a sectional view taken along line A-A of Fig. 1; Fig. 3 is a front elevational view of the magnetic head device of Fig. 1 as viewed from a side contactable with a recording medium; Fig. 4 is a schematic perspective view of a second embodiment of a magnetic head device of the present invention; Fig. 5 is a sectional view taken along line B-B of Fig. 4. Referring to Figs. 1 and 2, a magnetic head device as a first embodiment of the present invention has a substrate 11 made of a non-magnetic material on which are successively formed a lower magnetic layer (yoke) 12 made of a soft magnetic material, a first insulating layer 17 made of a non-magnetic material, and an upper magnetic layer (yoke) 23. The first insulating layer 17 forms a gap between the upper and lower magnetic layers at portions thereof for abutting a recording medium. The second insulating layer 14 is provided between the first insulating gap layer 17 and the upper magnetic layer 23 so as to be enveloped by these two layers. A conductive coil 15 is embedded in the second insulating layer 14. The upper magnetic layer 23 is composed of two layers: namely, a soft magnetic layer 20 disposed on the lower side and having a small coercive force and a soft magnetic layer 21 disposed on the upper side and having a large coercive force. Referring to Fig. 3, the breadth of the soft magnetic layer 20 is determined to provide a predetermined reproduction track width T2, while the breadth of the coercive layer 21 is determined to provide a predetermined recording track width T1. The operation of this embodiment will be described with reference to Fig. 2. When the magnetic head device is used for recording, a recording current is supplied to the conductive coil 15 so as to produce a magnetic field which is introduced to the gap 17 through a magnetic circuit formed by the lower magnetic layer 12 and the upper magnetic layer 23 composed of the soft magnetic layers 20,21, whereby signals carried by the recording current are recorded in a recording medium. The intensity of the recording magnetic field is much greater than the coercive forces of the soft magnetic layers 20,21 so that the magnetic field equally penetrates these two soft magnetic layers, so that the recording is conducted with a recording pattern width T1 (see Fig. 3). When the magnetic head device is used for reproducing, a signal magnetic field from the magnetic recording medium is introduced to the upper magnetic layer 23. The intensity of the signal magnetic field, however, is so small that the greater part of this magnetic field penetrates the soft magnetic layer 20 having a smaller coercive force. Thus, reproduction is conducted with a reproduction track width T2. According to the invention, it is possible to employ different track widths in the recording and reproduction phases using the same magnetic head device. It is therefore possible to eliminate any reduction in reproduction output due to off-tracking, regardless of any possible running offset of the recording medium between the recording and the reproducing phases. It may happen that the soft magnetic layer partially invades an adjacent track, depending on the magnitude of the turning offset of the recording medium. However, magnetic flux from the adjacent track does not enter the magnetic head device because the soft magnetic layer 21 has a large coercive force, so that crosstalk can advantageously be avoided. A description will now be given of a second embodiment of the invention with reference to Figs. 4 and 5. Referring particularly to Fig. 5, the second embodiment of the magnetic head device of the present invention has a third insulating layer 33 formed on an upper side of the second insulating layer 14 of the structure as shown in Fig. 2. A magneto resistive element 30 made of a thin film of Ni-Fe or Ni-Co, is provided on the underside of the third insulating layer 33 so as to contact the second insulating layer 14A. The magnetic head device also has a magnetic layer 20A which is substantially the same as the soft magnetic layer 20 of Fig. 2 except that it is partly notched as at 34. The notch 34 is disposed above the magneto resistive element 30. The magneto resistive element 30 is adapted to be supplied with electrical driving power through electrodes 31 and 32 as shown in Fig. 4. The operation of the second embodiment of the magnetic head device will be described with specific reference to Fig. 5. When the magnetic head device is used for recording, a recording current is supplied to the conductive coil 15 so as to produce a magnetic field which is introduced to the gap 17 through a magnetic circuit composed of the soft magnetic layer 21 having a large coercive force and the lower magnetic layer 12, whereby the signals are recorded in a recording medium. Thus, the recording is conducted with a recording pattern width T1 which is the same as that of the soft magnetic layer 21 (see Fig. 3). When the magnetic head device is used for reproducing, a signal magnetic field from the recording medium is introduced to the magneto resistive element 30 through the soft magnetic layer 20 of small coercive force, whereby reproduction is conducted with a reproduction track width T2 which is equal to the width of the soft magnetic layer 20. In the first and second embodiments as described, a lower magnetic layer is formed on a substrate made of a non-magnetic material. This, however, is only illustrative and the combination of the non-magnetic substrate and the lower magnetic layer may be substituted by a ferromagnetic substrate. As will be understood form the foregoing description, according to the invention, it is possible to employ different track widths for recording and reproduction with a single magnetic head device, thus offering remarkable advantages such as elimination of a reduction in reproduction output regardless of any running offset of the recording medium and increase in crosstalk. In general, magnetic recording of digital signals is conducted with a magnetic field intensity of 1000 A/m or greater, while the intensity of the signal magnetic field derived from a recording medium is as low as 80 A/m or less. Therefore, by using a double-layered structure composed of a soft magnetic layer of 80 A/m or greater and a soft magnetic layer of 80 A/m or less, it is possible to introduce the signal magnetic field from the recording medium only to the soft magnetic layer having a smaller coercive force, thus enhancing the above-described advantages of the invention.

Claims: A magnetic head device comprising a substrate (11), a lower yoke (12) formed on said substrate (11), an upper yoke (23; 23A) which forms a magnetic gap at an end thereof adjacent a surface of said lower yoke (12) for making a sliding contact with a recording medium, a conductive coil (15) which winds around a magnetic circuit formed by said lower and upper yokes (12,23;12,23A), wherein the upper yoke (23) forms a coupling magnetically at its other end with the lower yoke (12) and at least one of said lower and upper yokes (12,23; 12,23A) has a double-layered soft magnetic structure comprising two soft magnetic layers (20,21;20A,21) having different levels of coercive force, such that one of the soft magnetic layers (20;20A) which is located on an inner side of said magnetic circuit has a smaller coercive force than that of the other soft magnetic layer (21) and the width of the soft magnetic layer (21) having the greater coercive force, at least at a portion thereof for contacting with a recording medium, is greater than the width of the soft magnetic layer (20;20A) having the smaller coercive force when viewed from a side for making contact with a recording medium, characterised in that the layer (20;20A) with the smaller coercive force of the at least one of said lower and upper yokes (23;23A) is formed directly on the other layer (21) having the higher coercive force. A magnetic head device according to claim 1, characterised in that a part of the soft magnetic layer (20A) having the smaller coercive force is cut-away and substituted by a magneto resistive element (30) and electrode means (31,32) are provided for supplying driving electric current to said magneto resistive element (30). A magnetic head device according to claim 1 or claim 2, characterised in that one of said soft magnetic layers (20;20A) of the at least one of said lower and upper yokes (23;23A) has a coercive force of 80 A/m or less, while the other of said soft magnetic layers (21) has a coercive force of 80 A/m or greater.

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