Abstract:
A thin film magnetic head used for a magnetic disk device. The thin film magnetic head comprises two magnetic layers, a magnetic insulating layer sandwiched between the magnetic layers, an intermediate magnetic layer which is thinner than the magnetic layers, and an intermediate magnetic insulating layer formed in the vicinity of a gap surface between the intermediate magnetic layer and one of the magnetic layers. A track width in the gap surface of the intermediate magnetic layer is narrower than a track width in the gap surface of the two magnetic layers.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a thin film magnetic head used for a magnetic disk device or the like. 
     2. Description of the Prior Art 
     A construction of a thin film magnetic head of this kind in the prior art will be described with reference to FIGS. 6 and 7. 
     In these figures, reference numeral 1 designates a substrate formed of non-magnetic material (such as glass, ceramics, etc.); 2 and 3 upper and lower magnetic layers formed of magnetic material (such as Permalloy, Sendust, amorphous alloy, etc.); 4 a magnetic insulating layer formed of non-magnetic material (such as SiO 2 , Al 2  O 3  or resin); 5 a protective layer formed of non-magnetic material (such as SiO 2 , Al 2  O 3  or resin); and 6 a conductive coil formed of a conductive material (such as gold, silver, copper, aluminum, etc.). The thin film magnetic head is formed by a method which comprises forming the lower magnetic layer 3 on the substrate 1 using a method such as sputtering, forming the magnetic insulating layer 4 on the lower magnetic layer 3 using sputtering or the like and forming the conductive coil 6 within the magnetic insulating layer 4, and further successively forming the upper magnetic layer 2 and the protective layer 5 using sputtering or the like to thereby form a gap G on a gap surface 7. 
     In the operation of the thin film magnetic head constructed as described above, in the case where a signal is recorded in a magnetic recording medium (not shown), a signal current is applied to the conductive coil 6 to thereby magnetize the upper and lower magnetic layers 2 and 3, and the magnetic flux is outside the thin film magnetic head in the gap on the gap surface 7 of the thin film magnetic head to record a signal in a magnetic recording medium (not shown) adjacent to the gap surface 7 as a change of a magnetic pole. Conversely, in the case where a signal recorded in the magnetic recording medium is reproduced, a signal recorded as a change of the magnetic pole on the magnetic recording medium is detected at the gap G whereby the magnetic field in the upper and lower magnetic layers 2 and 3 is changed. A current is produced in the conductive coil 6 sandwiched between the upper and lower magnetic layers 2 and 3 due to the electromagnetic induction caused by the change of the magnetic field, and the current is sent to outside the thin film magnetic head as a signal. 
     In the above-described thin film magnetic head, recording and reproduction of a signal to the magnetic recording medium are carried out by one and the same gap G. However, the spacing (gap width) of the gap G suitable for recording operation and the gap width suitable for reproduction are in the relationship contrary to each other. That is, the narrower the gap width at the time of reproduction with respect to the recording wavelength of the signal on the magnetic recording medium, the smaller the frequency loss at the time of reproduction, and the reproduction efficiency is improved. Conversely, at the time of recording, the narrower the gap width with respect to the recording wavelength, the larger the gap loss at the time of recording, and the recording efficiency lowers. Therefore, in the actual thin film magnetic head, the gap width so as to minimize the lowering of the reproduction efficiency and the recording efficiency has to be set and the operation efficiency of the thin film magnetic head is to be lowered, posing a great obstruction in providing a high resolving power. 
     The present invention has been achieved in view of the aforementioned point. It is an object of the present invention to provide a thin film magnetic head in which two kinds of gaps are formed whereby the operating efficiency, particularly the operating efficiency during reproduction, is improved and high resolving power is provided. 
     SUMMARY OF THE INVENTION 
     According to a feature of the present invention, there is provided (see FIG. 3) a thin film magnetic head comprising an upper and lower magnetic layers 2 and 3 formed of a magnetic material, a magnetic insulating layer 4 formed of a non-magnetic material sandwiched between said upper and lower magnetic layers 2 and 3, an intermediate magnetic layer 10 formed along one of said upper and lower magnetic layers 2 and 3, said intermediate magnetic layer 10 being thinner than said upper and lower magnetic layers 2 and 3, and an intermediate magnetic insulating layer 11 formed in the vicinity of at least gap surface 7 between said intermediate magnetic layer and one of said upper and lower magnetic layers 2 and 3. 
     According to another feature of the present invention (see FIG. 3), a track width T R  in the gap surface 7 of the intermediate magnetic layer 10 is formed to be narrower than a track width T W  in the gap surface 7 of said upper and lower magnetic layers 2 and 3. 
     Since the upper and lower magnetic layers 2 and 3 form a recording gap G W  and the intermediate magnetic layer 10 and the lower magnetic layer 3 form a reproducing gap G R , the reproducing gap G R  can be set independently of the recording gap G W . Therefore, the reproducing gap G R  is formed to be narrow and the intermediate magnetic layer 10 constituting the reproducing gap G R  is formed to be thin, whereby the operating efficiency (reproducing efficiency) during reproduction can be enhanced without almost changing the operating efficiency (recording efficiency) during recording of the thin film magnetic head as compared with prior art, and a fine signal is easily detected, improving a resolving power. 
     Furthermore, since the intermediate magnetic layer 10 acting during reproduction can be set independently of the upper and lower magnetic layers 2 and 3, the track width (reproducing track width) T W  of the intermediate magnetic layer 10 can be set to be narrower than the track width (recording track width) T R  of the upper and lower magnetic layers 2 and 3 to thereby increase an off track margin for reproduction. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIGS. 1 to 4 show an embodiment of the present invention. 
     FIG. 1 is a schematic structural view of a thin film magnetic head according to the present invention; 
     FIG. 2 is an enlarged view showing essential parts of a gap surface in a thin film magnetic head; 
     FIG. 3 is an enlarged view showing essential parts of a gap surface according to the present invention; 
     FIG. 4 is a schematic structural view of another embodiment according to the present invention; 
     FIG. 5 is a view showing the relationship between a gap width with respect to a recording wavelength and a gap loss; 
     FIG. 6 is a schematic structural view of a conventional thin film magnetic head; and 
     FIG. 7 is an enlarged view showing essential parts of a gap surface of the prior art. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     An embodiment of the present invention will be described hereinafter with reference to FIGS. 1 and 2, in which the same parts as those in the prior art are indicated by the same numerals and the description thereof is omitted. 
     In this embodiment, reference numeral 10 designates an intermediate magnetic layer formed of a magnetic material (such as Permalloy, Sendust, amorphous alloy, etc.), and 11 denotes an intermediate magnetic insulating layer formed of a non-magnetic material (such as SiO 2 , Al 2  0 3  or resin). The intermediate magnetic layer 10 is formed on the magnetic insulating layer 4 formed similarly to prior art so that the layer 10 is thinner than the upper and lower magnetic layers 2 and 3 by a sputtering method or the like; then, the intermediate magnetic insulating layer 11 is selectively formed in the vicinity of the gap surface of the intermediate magnetic layer 10 by a sputtering method or the like; and thereafter the upper magnetic layer 2 and the protective layer 5 are formed similarly to the prior art to constitute a thin film magnetic head. 
     In the above-described structure, the recording gap G W  is formed by the upper magnetic layer 2 and the lower magnetic layer 3, and the gap width R of the reproducing gap G R  is formed to be narrower than the gap width W of the recording gap G W  by the intermediate magnetic layer 10 and the lower magnetic layer 3. The gap width R of the reproducing gap G R  is set to be considerably narrower than the recording wavelength on the magnetic recording medium so as to reduce the gap loss during reproduction, and the gap width W of the recording gap G W  is set to have a gap width so that the gap loss during reproduction is large and a signal cannot be detected. The gap width W of the recording gap G W  is decided as follows, for example: 
     First, a gap loss L g  during reproduction is roughly expressed by the following equation. ##EQU1## g: gap width λ: recording wavelength on a magnetic recording medium 
     This equation (1) is graphically shown in FIG. 5. As will be understood from FIG. 5, the gap width is present in which the gap loss during reproduction in a certain recording wavelength is the maximum. In FIG. 5, when the gap width is the same as or a multiple of the recording wavelength, the gap loss is the maximum. The gap width W of the recording gap G W  is set to this condition. 
     According to the above-described setting, at the time of reproduction, the reproducing gap G R  is small in the gap loss during reproduction since the gap width R is formed to be considerably narrow with respect to the recording wavelength, and the signal can be efficiently detected. Since the intermediate magnetic layer 10 is formed to be thin, even a fine variation in magnetic pole on the magnetic recording medium, a magnetic field within the intermediate magnetic layer 10 tends to be varied to improve a sensitivity of signal detection. Furthermore, since at that time, the recording gap G W  is large in gap loss during reproduction, a signal is not detected. 
     Next, at the time of recording, the upper, lower and intermediate magnetic layer 2, 3 and 10 are magnetized by a signal current flowing through the conductive coil 6 within the thin film magnetic head. However, since the intermediate magnetic layer 10 is formed so that a saturated magnetic flux amount thereof is smaller than the upper and lower magnetic layers 2 and 3, the intermediate magnetic layer 10 is apparently the same as the upper magnetic insulating layer 4 because the magnetic flux becomes saturated, and the reproducing gap G R  becomes invalid. In the recording gap G W  formed by the upper and lower magnetic layers 2 and 3, a signal is recorded on the magnetic recording medium. The gap loss during recording is not so rapidly changed as in the gap loss during production as far as about the same adequate gap width with respect to the recording wavelength exists. The gap loss during recording does not change so much as compared with the prior art. 
     FIG. 3 shows a second embodiment according to the present invention. The width (reproducing track width) T R  in the lateral direction in the gap surface 7 of the intermediate magnetic layer 10 according to the present invention is formed to be narrow as compared with the width (recording track width) in the lateral direction of the upper and lower magnetic layers 2 and 3. According to the invention, the intermediate magnetic layer 10 used for reproduction is formed independently of the upper and lower magnetic layer 2 and 3. Therefore, as shown in FIG. 3, the reproducing track width T R  of the intermediate magnetic layer 10 is formed to be narrower than the recording track width T W  formed by the upper and lower magnetic layers 2 and 3 whereby an off track margin in the lateral direction of the thin film magnetic head during reproduction can be increased with respect to the track width of the recording signal on the magnetic recording medium. 
     It is noted that the equation (1) in the above-described embodiment is a simplified equation used to facilitate the discussion of the present invention. The characteristic of the thin film magnetic head is not determined by the equation (1) and the present invention is not limited thereby. 
     While in the above-described embodiment, the intermediate magnetic insulating layer 11 is formed merely in the vicinity of the gap surface 7 between the upper magnetic layer 2 and the intermediate magnetic layer 10, it is to be noted that the intermediate magnetic insulating layer 11 may be formed on the whole surface between the upper magnetic layer 2 and the intermediate magnetic layer 10, as shown in FIG. 4, and that the intermediate magnetic layer 10 may be formed of a material having a low saturated magnetic flux density as compared with a material for the upper and lower magnetic layers 2 and 3, to thereby more positively invalidate the function of the intermediate magnetic layer 10 during recording. 
     Furthermore, the lateral width of the intermediate magnetic layer 10 in the second embodiment of the present invention will suffice to be narrower than the lateral width of the upper and lower magnetic layers 2 and 3, and the whole intermediate magnetic layer 10 may be formed to be narrower than the lateral width of the upper and lower magnetic layers 2 and 3. 
     In the thin film magnetic head according to the present invention, as described above, the recording gap G W  is formed by the upper and lower magnetic layers 2 and 3 and the reproducing gap G R  is formed by the lower and intermediate magnetic layers 3 and 10. Therefore, the reproducing efficiency only can be rapidly enhanced without much changing the recording efficiency. In addition, the intermediate magnetic layer 10 is formed to be thinner than the upper and lower magnetic layers 2 and 3, whereby the sensitivity of signal detection on the magnetic recording medium is improved. This can also be provided with the high resolving power. 
     Moreover, since the intermediate magnetic layer 10 is formed independently of the upper and lower magnetic layers 2 and 3, the reproducing track width T R  of the intermediate magnetic layer 10 is formed to be narrower than the recording track width T W  of the upper and lower magnetic layers 2 and 3, whereby an off track margin during reproduction can be increased.