Thin film magnetic head

Abstract: The head includes an upper magentic layer comprising a first yoke (6), a portion of which is divided into front and rear sections and which is provided near the divided sections with a magneto-resistive element (5), a second yoke (7) provided adjacent to the opposite ends of the first yoke in a widthwise direction of a recording track and a third yoke (28) provided between the first yoke and the second yoke and having a larger magnetic reluctance than those of the first and second yokes. In the above constitution, the first, second and third yokes can be mainly used in recording to record in an area of a large width (TW) on the recording medium, and only the first yoke can be used in reproducing to reproduce in an area of a small width (TR) on the recording medium, so that the reproducing output is not reduced when the recording medium experiences a running deviation.

Description: The present invention relates to a thin film magnetic head for use with a magnetic recording apparatus, and, more particularly, to a thin film magnetic head in which a recording head and a reproducing head are formed integrally with each other. A prior inductive head produces a reproducing output proportional to running speeds of a recording medium. On the other hand, a thin film magnetic head using the magnetoresistance effect is not dependent upon a relative speed between the head and a recording medium and produces a constant reproducing output such that the output is not reduced even when such relative speed is small. Accordingly, this type of thin film magnetic head has been widely used with magnetic recording equipment in recent years. However, since such a thin film magnetoresistive head is not capable of recording, it must be combined with an inductive thin film head of a coil type in order to provide both recording and reproducing functions. An example of such a thin film magnetic head is disclosed in Japanese Patent Unexamined Publication Nos. 52-12814 and 61-48116. In a prior thin film magnetic head, lower and upper magnetic layers are linearly extended in opposed relationship with each other on a substrate, and these magnetic layers and a magnetic gap formed therebetween constitute a magnetic circuit. In addition, a coil layer is formed around the magnetic circuit. The upper magnetic layer is divided into front and rear sections, and a magnetoresistive element is arranged to bridge these sections. A thin film magnetic head of this type is disclosed in WO 88/07741 and comprises a thin film magnetic head including a non-magnetic substrate, a lower magnetic layer formed on said substrate, non-magnetic layers constituting magnetic gaps provided on said lower magnetic layer, an upper magnetic layer including a first yoke divided into front and rear sections, a magnetoresistive layer having electric current supply means provided below the upper magnetic layer, and a coil layer surrounded by a magnetic circuit consisting of the lower and upper magnetic layers and the magnetic gaps. This thin film magnetic head acts in the manner described hereinbelow. In recording, a recording current flows through the coil layer, so that a recording magnetic field leaks to the outside through the magnetic gap; writing on a recording medium is performed by the resultant leaking magnetic field. In reproducing, a signal magnetic flux generated from the recorded medium passes through the magnetic gap and the front section of the upper magnetic layer to flow into the magnetoresistive element. The signal is detected form the resistance change of the magnetoresistive element. More specifically, a sensing current is applied to the magnetoresistive element and the resistance change of the element is transformed into a voltage change such that the signal can be read. However, a prior thin film magnetic head such as this can not provide favourable recording and reproducing in the case where the recording medium has poor running accuracy because the track width is the same in recording and reproducing. More specifically, assuming that the prior thin film magnetic head has a recording and reproducing track width T₁ and the recording medium has a running accuracy of ± a, the maximum running deviation in recording and reproducing will become 2a and the effective reproducing track width will become T₁ - 2a, which means a reduction in the reproducing output. It is an object of the present invention to solve the problems of the prior art and to provide a thin film magnetic head capable of performing favourable magnetic recording and reproducing. To this end, the invention provides a thin film magnetic head characterised in that the upper magnetic layer is divided to provide the first yoke, second yokes adjacent to opposite ends of said first yoke in a widthwise direction of a recording track and third yokes between said first and second yokes, said third yokes having a larger magnetic reluctance than that of said first and second yokes, and wherein a reproduction width of the track is defined by the width of the first yoke and a recording width by the widths of the first, second and third yokes. The larger magnetic reluctance may be achieved by making the third yokes thinner. If their thickness is reduced to zero, then in fact air gaps remain. This is expressed in independent claim 6. In the above constitution of the invention, the first and second yokes can be used mainly to wide-record on the recording medium, and only the first yoke can be used to narrow-reproduce on the recording medium, so that the reproducing output is not reduced when the recording medium experiences running deviation. The features of the invention will be more readily understood from the following description of preferred embodiments with reference to the drawings, of which:- Fig. 1A is a plan view of a thin film magnetic head according to a first preferred embodiment of the invention; Fig. 1B is a cross-sectional view taken along line IB - IB of Fig. 1A; Fig. 1C is a front view of the thin film magnetic head of Fig. 1A as viewed from a sliding surface of a recording medium; Fig. 2 is a plan view of a thin film magnetic head according to a second embodiment of the invention; Fig. 3A is a plan view of a thin film magnetic head according to a third embodiment of the invention; Fig. 3B is a cross-sectional view taken along line IIIB - IIIB of Fig. 3A; Fig. 3C is a front view of the thin film magnetic head of Fig. 3A as viewed from a sliding surface of a recording medium; and Fig. 4 is a plan view of a thin film magnetic head according to a fourth embodiment of the invention. As shown in Figs. 1A to 1C, a thin film magnetic head according to a first embodiment of the invention includes a non-magnetic substrate 1 made of ceramics, glass or the like, a lower magnetic layer 2 formed of a soft magnetic material such as permalloy, sendust or the like by a sputtering process and provided on the non-magnetic substrate 1 to have the same width as that of a recording track, a gap layer 3 made of an insulating material (SiO₂) and provided on the lower magnetic layer 2, a conductor coil 4 formed on an insulating layer 10, a magnetoresistive element 5 made of a nickel-iron alloy and provided on the insulating layer 10, and first and second yokes 6 and 7 each made from permalloy or sendust by sputtering and divided into front and rear sections. The first yoke 6, magnetoresistive element 5, gap layer 3 and the lower magnetic layer 2 cooperate to form a magnetic circuit which surrounds the conductor coil 4. The second yokes 7 are arranged at positions spaced by a distance X from the first yoke 6 in the widthwise direction of the recording track. Provided contiguous to the first and second yokes are third yokes 28 which are positioned therebetween so as to be contacted by the recording medium and have a larger magnetic reluctance than those of the first and second yokes 6 and 7. Like the first yoke, the second and third yokes cooperate with the gap layer 3 and the lower magnetic layer 2 to form magnetic circuits which surround the conductor coil 4. Furthermore, at the opposite ends of the magnetoresistive element 5 are provided electrodes 8 for reproducing only a signal magnetic field which is generated from the recording medium by the first yoke 6. In operation, a recording current is applied to the conductor coil 4, and the induced magnetic field for recording is directed to the gap layer 3 through the magnetic circuit comprising the first yoke 6 and the lower magnetic layer 2 and through the magnetic circuits comprising the second yokes 7 and the lower magnetic layer 2 so that recording is effected on the recording medium. Simultaneously, the magnetic field for recording flows into the third yokes 28. As a result, the width Tw of the recording track is the sum of the widths of the first, second and third yokes. In reproducing, the magnetic field from the recording medium is conducted mainly through the first and second yokes 6 and 7. However, since the third yokes 28 are provided between the first and second yokes 6 and 7 and the magnetic reluctance of the third yokes 28 is larger than that of the first and second yokes, the magnetic field conducted through the second yokes 7 will not flow into the magnetoresistive element 5, so that the width of the first yoke 6 substantially defines a width of the reproducing track. The thin film magnetic head is constructed such that the recording track width Tw and the reproducing track width Tr make Tw ≧ Tr + 2a, so that even when the running deviation of the recording medium becomes 2a at maximum in recording and reproducing, the reproducing track is included within the recording track and presents the reproducing signal output from being lowered. Furthermore, when a second yoke 7 enters into an adjacent track due to a running deviation of the recording medium, the signal magnetic field in the adjacent track flows into the yoke 7, but will not flow into the magnetoresistive element 5 since the third yoke provided between said second yoke 7 and the first yoke 6 has a larger magnetic reluctance than that of the first and second yokes. Accordingly, good reproduction with little cross talk can be obtained. With reference to Fig. 2, a second embodiment of the invention will be described hereinbelow. In Fig. 2, the same parts as those shown in Figs. 1A to 1C are designated by the same reference numerals, and the explanation thereof is omitted. The second embodiment is different from the first embodiment in that second yokes 17 are divided into front and rear sections, like the first yoke 6. As the result, the magnetic circuit comprising the lower magnetic layer 2 and the first yoke 6 and the magnetic circuits comprising the lower magnetic layer 2 and the second yokes 17 are substantially identical to each other in constitution. Thus, in recording, a magnetic field generated by applying a recording current to the conductor coil 4 passes through the magnetic circuits comprising the lower magnetic layer 2 and the second yokes 7 to reach the respective magnetic gaps, thus generating recording magnetic fields of substantially the same strength. Accordingly, dispersion in the quality of recording over the recording medium is reduced. To improve such effect, dummy magnetoresistive elements may be provided on the divided sections of the second yokes 17. Figs. 3A to 3C show a third embodiment of the invention. In Figs. 3A to 3C, the same parts as those of the first and second embodiments are designated by the same reference numerals. In the third embodiment, third yokes 18 are formed to have a thinner film thickness and a larger magnetic reluctance than those of the first yoke 6 and the second yokes 17. The third embodiment operates in substantially the same manner as the first and second embodiments, thus providing substantially the same effect as that of the preceding embodiments. Fig. 4 shows a plan view of a thin film magnetic head according to a fourth embodiment of the invention, in which the second yokes 7 are arranged at positions laterally spaced by a distance X from the opposite ends of the first yoke 6. Accordingly, the recording track width Tw is the sum of the widths of the first yoke 6, the second yokes 7 and the distances X of the gaps between the first yoke 6 and the second yokes 7. The width of the reproducing track corresponds to the width T R of the first yoke 6. In this embodiment, portions of the recording tack corresponding with the gaps X are in non-recording condition, so that the width of the effective reproducing track is represented by the equation T R ' = T R - X when the recording medium experiences running deviations. However, if the distance X is sufficiently small as compared with the width T R of the first yoke 6, the reproducing output is little affected by such running deviations. Accordingly, favourable recording and reproducing can be effected. In the third and fourth embodiments, the second yokes 7 may be divided into front and rear sections in a similar manner to the second embodiment. Although the recording track width is defined with the upper and lower magnetic layers set at the same width in all of the embodiments, upper and lower magnetic layers having different widths to provide a magnetic layer of a small width may define the width of the recording track. Furthermore, it is possible that in reproduction an electric current passes through the conductor coil 4 to apply a bias magnetic field to the magnetoresistive element 5, thereby improving reproduction sensitivity.

Claims: A thin film magnetic head including a non-magnetic substrate (1), a lower magnetic layer (2) formed on said substrate (1), non-magnetic layers (3,10) constituting magnetic gaps provided on said lower magnetic layer (2), an upper magnetic layer (6) including a first yoke (6) divided into front and rear sections, a magnetoresistive layer (5) having electric current supply means (8) provided below the upper magnetic layer (6), and a coil layer (4) surrounded by a magnetic circuit consisting of the lower (2) and upper (6) magnetic layers and the magnetic gaps, characterised in that the upper magnetic layer (6) is divided to provide the first yoke (6), second yokes (7;17) adjacent to opposite ends of said first yoke (6) in a widthwise direction of a recording track and third yokes (28;18) between said first (6) and second (7;17) yokes, said third yokes having a larger magnetic reluctance than that of said first and second yokes, and wherein a reproduction width of the track is defined by the width of the first yoke and a recording width by the widths of the first, second and third yokes. A thin film magnetic head as set forth in claim 1, characterised in that said magnetoresistive element (5) is disposed adjacent to the divided sections of said first yoke (6). A thin film magnetic head as set forth in claim 1 or claim 2, characterised in that said second yokes (17) are divided into front and rear sections at positions corresponding to the divided sections of said first yoke (6) and over substantially the same area as that of said first yoke (6). A thin film magnetic head as set forth in any preceding claim, characterised in that said first (6), second (17) and third yokes (18) are made of the same soft magnetic material, and said third yokes (18) have a thinner film thickness than that of said first (6) and second (17) yokes. A thin film magnetic head as set forth in claims 1 and 4, characterised in that said third yokes (18) are formed between said first (6) and second yokes (18) at positions where they are contacted by the recording medium. A thin film magnetic head including a non-magnetic substrate (1), a lower magnetic layer (2) formed on said substrate (1), non-magnetic layers (3,10) constituting magnetic gaps provided on said lower magnetic layer (2), an upper magnetic layer (6) including a first yoke (6) divided into front and rear sections, a magnetoresistive layer (5) having electric current supply means (8) provided below the upper magnetic layer (6), and a coil layer (4) surrounded by a magnetic circuit consisting of the lower (2) and upper (6) magnetic layers and the magnetic gaps, characterised in that the upper magnetic layer (6) is divided to provide the first yoke (6), second yokes (17) adjacent to opposite ends of said first yoke (6) in a widthwise direction of a recording track with predetermined air gaps therebetween, wherein a reproduction width of the track is defined by the width of the first yoke (6) and a recording width by the widths of the first and second yokes and said air gaps.

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