MAGNETIC HEAD AND METHOD OF PRODUCING SAME

Abstract: In a magnetic head comprising a head gap and a magnetic core composed of both a high permeability ferrite and a magnetic alloy, said magnetic alloy being disposed in the vicinity of said head gap, the improvement comprising a corrugation provided at a junction portion between said ferrite and said magnetic alloy, a height of said corrugation being not less than a value of the longest wavelength of luminance signals and color signals recorded on a magnetic recording medium, a distance defined between adjacent two crests or bottoms of said corrugation being smaller than a width of a head track.

Description: The present invention relates to a magnetic recording and/or reproducing apparatus, of the type having a magnetic head, magnetic tape and means for transporting said tape past said head, said magnetic head compromising a magnetic core composed of a high permeability ferrite in combination with a magnetic alloy, wherein said magnetic alloy has a high saturation flux density and is disposed on both sides of said head gap, a first corrugation provided along a first interface of said ferrite and said magnetic alloy and a second corrugation provided along a second interface of said ferrite and said magnetic alloy, wherein adjacent two crests or bottoms of respective first and second corrugations are separated by a distance (P) which is smaller than the track width (W). Such a head is already known from EP-A-125891. Magnetic tapes made of Fe or Co alloy powder have been used to improve the recording density but a coercive force Hc of a magnetic tape made of the alloy powder has a high value, ranging from 1,300 to 1,500 Oe. In order to record/reproduce the signal to/from such a high Hc tape, a metal head of a sendust or an amorphous material is used and, conventionally, metal heads of a variety of constructions have been proposed. However, when the head core is formed solely of the magnetic alloy, the eddy current loss is great and, particularly when used with high frequency signals, such as video signals, operating characteristics of the head are significantly degraded. Consequently, in such heads it is proposed to adopt a combination of both a ferrite magnetic material and a magnetic alloy material, in which only a head gap portion is made of the magnetic alloy and the other head core portion is made of the ferrite magnetic material. In the magnetic head according to this construction, the bonding portion between the ferrite material and the magnetic alloy acts as the pseudo-gap and picks up interface signals, which deteriorates the signal to noise (SN) ratio. To eliminate this problem, in the magnetic head described in Japanese laid-open Patent publication No. 155 513/1983, a protrusion is provided on the surface of the ferrite by mechanical processing and a magnetic alloy material is deposited on both side faces of the above protrusion by sputtering to form a head gap by the above alloy magnetic layer, so that the head gap and the junction portion between the ferrite and the magnetic alloy are not parallel to each other. In addition, as described in Japanese laid-open Patent publication No. 175 122/1983, grooves are provided along a ferrite material and a magnetic alloy material is filled within the above grooves to obtain a similar effect as in the previously identified publication. Furthermore, in Japanese laid-open Patent publication No. 125 906/1985, an inclined portion is provided on the surface of the ferrite by mechanical processing and on the inclined portion, a magnetic alloy material is deposited to have a thickness corresponding to a track width of the head, while the head gap portion is formed from a magnetic alloy material and a head gap and a junction portion, formed between the ferrite and the magnetic alloy materials, are made unparallel to each other. However, any one of the above-described prior art disclosures involves a complicated process in manufacturing the head, showing disadvantages in applying it to mass production. An object of the present invention is to eliminate the problem, present in the prior art, caused in the composite type magnetic head composed of the magnetic core made of, for example, a magnesium-zinc ferrite and a magnetic alloy such as amorphous magnetic alloy, ie problems relating to the reduction of SN ratio, with respect to recording and reproducing signals due to the action of the junction of both magnetic materials acting as the psuedo-gap, while providing a magnetic head suitable for mass production. Another object of the present invention is to provide a composite type magnetic head composed of the magnesium-zinc ferrite and a magnetic alloy, such as the amorphous alloy, and a method of making the same, wherein, during recording, it is possible to provide a recording magnetic field by which, even with metal tape having a high Hc, the magnetic head can sufficiently record thereon while the loss suffered during reproduction can be reduced, thereby obtaining a substantially improved reproduction output. According to the present invention, there is provided a magnetic recording and/or reproducing apparatus of the aforesaid type, characterised in that said corrugations of the magnetic head are of a height (D) which is not less than the value of the longest wavelength of said signals recorded on said magnetic medium. The invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figs. 1a and 1b show a perspective view, illustrating an embodiment of the magnetic head according to the invention, Fig. 2 shows an enlarged view, illustrating a head-gap portion of the sliding contact surface according to the invention, Fig. 3 shows a view, illustrating an example of the manufacturing process of the head according to the present invention, Figs. 4 and 5 show another embodiment, wherein the corrugated portions are defined on the ferrite substrate, Fig. 6 shows an enlarged view, illustrating the gap portion of the sliding contact surface of the head which is one of the features of the invention, Figs. 7a and 7b show perspective views, illustrating another embodiment of the magnetic head according to the invention, Figs. 8 (a) and (b) show explanatory views of a part of the process for manufacturing the magnetic head having the construction depicted in Fig. 7. Figs. 9a and 9b are perspective view of another embodiment of the magnetic head embodying the present invention, Fig. 10 is a partially enlarged view of a gap portion of the head shown in Fig. 9, and Fig. 11a, 11b, 11c, 11d and 11e are drawings illustrating a process of producing the magnetic head of Fig. 9. DETAILED DESCRIPTION OF THE EMBODIMENTS Figs. 1a and 1b are enlarged perspective views illustrating an example of the magnetic head according to the invention, in which Fig. 1a there are removed coil windings 10 and terminals 12. In Fig. 1a, reference numerals 1 and 2 show the magnetic core made of the Mn-Zn ferrite material. Magnetic alloys 3 and 4 such as the amorphous alloy of Co 82.9 Nb 10.9 Zr 4.0 Ta 2.2 or sendust of Fe₈₅ Si 9.5 Al 5.5 , which have a highly saturation magnetic flux density was deposited by sputtering on the faces opposed to the head gap 5 of those cores 1 and 2, and the thin layer of the non-magnetic material such as the glass or the like was provided between the magnetic alloy 3 and 4 in a predetermined thickness to define the head gap 5. 6 and 6' show bonding members for bonding the left and right magnetic cores with each other and a glass was mainly used as the bonding member. 7 shows a window for coil winding. In Fig. 1, magnetic alloys 3 and 4 were disposed above the window 7 (i.e. at both sides of the head gap 5) and at both sides of the rear gap 5' which is located below the window 7. 9 shows a sliding contact surface in sliding contact with the magnetic tape and Fig. 2 shows the enlarged plan view of the adjacent portion of the gap of the sliding contact surface 9. The magnetic head according to the present invention is characterized in that the boundary portion between magnetic cores 1 and 2 and the magnetic alloys 3 and 4 is shaped in the alternate concave and convex form (corrugated form) and in that a height D of 4 to 6 µm defined between the crest and the bottom thereof is made equivalent to or more than the longest wavelength of the luminance signals and the color signals existing in video signals which are recorded onto the magnetic tape. For example, in a case of 8 milimeter type video, regarding the signals involved in the image, the wavelength of color signals which was converted into a low frequency is the longest, that is, about 5 µm. Consequently, in this case, the height of the corrugation is made not less than 5 µm. By adopting this constitution, the color signals which are picked up as interface signals at the point A on the junction portion 8, for example, become having an inversed phase in comparison with other interface signals which are picked up at a point B at which the distance L therebetween corresponds to the half wavelength, with the result that they are negated each other, causing no disturbance. As described above, since at points on the junction portions 8 and 8' between magnetic cores 1 and 2 and magnetic alloys 3 and 4 which points are separated by the half wavelength, the interface signals have respectively inversed phases with each other, they are negated as a whole, so that the disturbance caused by the pseudo-gap can be eliminated. Further, the magnetic head according to the invention is characterized in that the distance P of about 20 µm defined between adjacent two crests or bottoms of the corrugation is made smaller than the track width W of about 30 µm of the head. Consequently, every points on the junctions 8 and 8' will have a point which is offset by the half wavelength somewhere on the junction portion, which therefore allows to negate the interface signals. By the way, as in the 8 milimeter type video, when the record of the video signal onto the magnetic tape is partially overwritten, the above distance P is preferably made smaller than the effective width of the track which is recorded onto the magnetic tape. The present invention also provides a method for readily making the magnetic head having features as specified above. One example of the method is hereinafter described with reference to Fig. 3 and so on. First, as shown in Fig. 3 (a), a parallel slit-like resist coating layer 26 having a smaller pitch P of about 20 µm than the track width of the video head was formed on the surface A of the Mn-Zn ferrite substrate 25. Next, the ferrite substrate thus obtained was subjected to the electrolytic etching within the electrolytic solution, with the result that, as shown in Fig. 3 (b), a parallel slit-like corrugation was formed on the surface Q and the surface of the ferrite substrate 25 exhibits a corrugated surface Q'. Then, the pitch P of about 20 µm of the corrugation becomes equal to the pitch P of the parallel slit-like resist coating film. Furthermore, the height D of 4 - 6 µm of the corrugation can be controlled by the period of time of the electrolytic etching and, as shown above, is made equal to or more than the value of the longest wavelength existing in the video signals which are recorded on the magnetic tape. Next, as shown in Fig. 3 (c), the magnetic alloy 27 having a high saturation magnetic flux density such as an amorphous one was deposited by sputtering to have an appropriate thickness E of 30 - 40 µm on the surface Q'. In this case, it is necessary that the thickness E of magnetic alloy 27 is greater than the height D of the corrugation of the surface Q'. Subsequently, as shown in Fig. 3 (d), after the surface of the layer 27 of the magnetic alloy had been flattened by polishing, notched grooves 29 were provided, as shown in Fig. 3 (e), at one edge 28 of the magnetic alloy layer 27 to thereby form track portions 30. The width of the track portion 30 was made equal to the width W of about 30 µm of the track of the head. When the track portion 30 was formed, there is no limitation regarding the positional relationship between the corrugation present at the junction portion located between the ferrite and the magnetic alloy and the track portion 30, because in the track portion 30 there is included a corrugation having at least one cycle in view of the fact that the distance P of about 20 µm between adjacent two crests or bottoms thereof is smaller than the width W of about 30 µm of the track portion 30. Then, as shown in Fig. 3 (f), the molten glass was filled into the notched grooves 29. As the occasion demands, a groove 32 may be provided rearwardly of the ferrite substrate 25, in which groove the glass 31 can be also filled. Subsequent thereto, by polishing the surface of the magnetic alloy layer 27, the overcoated excessive glass on the cut-in groove was removed, while the surface of the magnetic alloy layer 27 was finished to have a very smooth surface like a mirror. Both the substrate thus made and another substrate obtained by joining the ferrite and magnetic alloy in the same manner as described above and provided with a groove 33 for coil winding are prepared, a gap material such as SiO₂ or the like being provided by sputtering in the predetermined thickness on the surface of the mirror-finished face of at least one of those substrates, and a gap bar having the gap 34 is made by bonding both substrates via the gap material, as shown in Fig. 3 (g). Then, as shown by the dotted line 35, the magnetic head according to the invention was obtained by cutting the gap bar through the substantially central portion of the notched grooves 29 at a predetermined angle relative to the gap 34. Although, in Fig. 3 (b), the corrugation of the substrate 25 is defined parallel to the surface F, the parallel-slit-like resist coating film 26 may be formed at a certain angle relative to the surface F, as shown in Fig. 4. Furthermore, the parallel slit-like resist coating film need not be rectilinear but may be curved as shown in Fig. 5 without nullifying the advantage obtained in the invention. As shown in Figs. 4 and 5, since the corrugation is formed onto the surface of the ferrite substrate of Fig. 3 by using the large flat ferrite substrate and the magnetic alloy was deposited onto the surface of the corrugation by sputtering, it becomes possible to improve the efficiency of the mass production system. Furthermore, in the manufacturing process of the head, points e and f of the convex portion of the ferrite surface can be formed in the sharp angle protrusion, as shown in Fig. 6, by properly selecting the conditions of electrolytic etching. When points of convex portions e and f are made to have a sharp angle, the height D thereof can be enlarged to reduce the affect of the pseudo-gap to a great extent. The second feature of the present invention is that positions of the convex portions e and f are made asymmetrical relative to the head gap 5. Namely, convex portions e and f are provided at positions where a straight line connecting convex portions e and f does not intersect at a right angle with the head gap 5. In case points of convex portions e and f form sharp angle, the magnetic potential of the protrusion can be increased, so that convex portions e and f are apt to act as gap. However, since, in this invention, the straight line g does not intersect at a right angle with the head gap 5, i.e. forms a certain angle relative to the direction in which the signal recorded onto the magnetic tape is magnetized, interface signals are hardly picked up due to the azimuth loss. When in the manufacturing process of the head in Fig. 3 (e) the track portion 30 is formed, the track portion can be formed irrespectively of the position of the convex portions provided in the junction position between the ferrite substrate 25 and the magnetic alloy 27. Consequently, when the gap bar is formed, as shown in Fig. 3 (g), by making the left and right cores butt against each other, since the position of the convex portion, which is provided at the junction portion between the ferrite material on the magnetic cores and the magnetic alloys, are respectively freely defined, they scarcely have a symmetrical position relative to the gap. Namely, since, in most cases, the line which connects the points of the convex portions on the left and the right magnetic cores does not intersect at a right angle with the gap, it becomes possible to obtain a magnetic head having a construction of Fig. 6 in which interface signals are hardly picked up. Figs. 7a and 7b show another embodiment of the magnetic head according to the invention in which Fig. 7a there are removed magnetic coils 10 and terminals 12, wherein the performance of the head is improved. The feature of the embodiment, depicted in Fig. 7 is that the thickness of magnetic alloys 3' and 4' disposed on both side of the rear gap 5' is made smaller than that of magnetic alloys 3 and 4 disposed on both sides of the head gap 5. Small thickness of magnetic alloys 3' and 4' can reduce the eddy current loss at that portion, thus improving the reproducing efficiency by the head. To obtain the head shown in Fig. 7, in place of the step shown in Fig. 3 (d) wherein the polishing of the magnetic alloy material provided on the ferrite substrate 25 is shown, the surface of the magnetic alloy on the ferrite substrate 25 is polished in such a way shown in Fig. 8 (a) that the surface of the magnetic alloy 27 was flattened and inclined so that the thickness T₁ of 10 - 25 µm at side H of the magnetic alloy was made greater than that T₂ of 0 - 5 µm at the rear portion thereof. In this case, more preferably, the inclination of the magnetic alloy was made greater during polishing, as shown in Fig. 8 (b), such that in the vicinity of the rear portion G the protruding portion S of the ferrite substrate 25 was exposed to the surface of the magnetic alloy 27. Then, the head track was formed on the side of magnetic alloy having a greater thickness. Figs. 9a and 9b show still another embodiment of the composite type magnetic head composed of the ferrite magnetic material and the magnetic alloy such as the amorphous one magnetic alloy in which Fig. 9a there are removed magnetic coils 10 and terminals 12, which is excellent in the performance of recording and reproducing and is readily produced. In this embodiment, magnetic alloys 3 and 4 were disposed only on both sides of the head gap 5 and not at the portion of the rear gap 5'. Fig. 10 shows an enlarged view when the gap portion is viewed from the direction of the arrow X, wherein a bonding material 6 was removed. 29 denotes a notched groove restricting the width of track of the head. The length K of 800 - 900 µm of magnetic alloys 3 and 4 disposed on both sides of the gap 5 which extends from the surface of the head to the depth of the gap was set to be shorter than a distance J of 700 - 800 µm defined between the surface of the head and the lower end of the window 7 for coil winding and shorter than the distance I of 500 - 600 µm defined between the surface of the head and the lower end of the notched groove 29 restricting the width of the track. In this manner, the magnetic alloy having the high saturation magnetic flux density such as the amorphous one was only disposed on the gap portion 5, with the result that during recording there can be obtained a recording magnetic field sufficiently high to effect the recording even with respect to the metal tape having a high Hc. Besides, since the magnetic alloy is not disposed at the portion of back gap 5', the loss caused during reproducing can be reduced compared with the prior embodiment, providing the greater reproduced signals. Fig. 11 shows an example of the manufacturing process of the magnetic head depicted in Fig. 9. First, as shown in Fig. 11 (a), by mechanical processing or chemical etching or the like, a recessed portion 43 was defined on a part of one surface 42 of the block 41 of the ferrite magnetic material to define a stepped portion 44. Next, the resist film was applied on the surface 42 on the ferrite block 41 and on the surface of the stepped portion 44, a mask 45 having a parallel slit-like pattern 46 was superimposed thereonto and the pattern 46 was printed onto the stepped portion 44 by rediating the light 47. In this state, the material thus obtained was subjected to the electrolytic etching, as shown in Fig. 3 (b), so that the corrugated surface 48 was formed on the surface of the stepped portion 44 while the surface 42 was maintained in the state of original plane surface without undergoing the etching action. Next, as shown in Fig. 11 (c), the magnetic alloy 49 such as the amorphous one was deposited by sputtering onto the plane 42 of the ferrite block 41 and on the corrugated surface 48. Subsequently, the surface of the magnetic alloy 49 was polished up to a position as indicated by the dotted line 50 to obtain the magnetic core block in which the magnetic alloy 49 is left on the corrugated surface 48 and in which the magnetic alloy was removed regarding the surface 42. Next, grooves restricting the track which grooves form a predetermined angle ϑ of about 12° relative to the polished surface 50 and reach the ferrite material 41 was provided, as shown by the dotted line 51, on the magnetic alloy 49 on the above corrugated surface 48 to obtain the half body of the magnetic core having a shape as depicted in Fig. 11 (d). In other words, in Fig. 11 (d), track restricting grooves 52 are sequentially defined within the magnetic alloy 49 to form the track portion 53. The depth M of 150 - 200 µm of the groove 52 was made greater than the thickness N of 10 - 25 µm of the magnetic alloy 49, while the length I of the groove 52 was made greater than the length K of the magnetic alloy 49. Subsequent thereto, the non-magnetic material 54 such as the glass or the like is filled into the grooves 52. Then, as shown in Fig. 11 (e), the window 55 for coil winding was provided on the surface 42. The distance between the lower end of the window 55 and the front surface 56 of the block 41 was made shorter than the length I of the track defining grooves 52. After those steps, the same step as shown in Fig. 3 (f) was effected and the magnetic head shown in Fig. 9 was obtained. When, as shown in Fig. 11 (e), a magnetic alloy is only disposed at the portion of the head gap to thereby provide a gap bar by use of the resultant half bodies of the magnetic core so that a magnetic head chip is obtained by cutting the gap bar, since no magnetic alloy is cut during the above operation, damage of the head or occurence of cracks caused by the blinding of the cutter can be prevented and the mass production is achieved with a high yield.

Claims: A magnetic recording and/or reproducing apparatus, having a magnetic head, magnetic tape and means for transporting said tape past said head, said magnetic head comprising a head gap (5), a magnetic core (1,2,3,4) composed of a high permeability ferrite (1,2) in combination with a magnetic alloy (3,4) wherein said magnetic alloy has a high saturation flux density and is disposed on both sides of said head gap, a first corrugation (8) provided along a first interface of said ferrite (1) and said magnetic alloy (3) and a second corrugation (8') provided along a second interface of said ferrite (2) and said magnetic alloy (4), wherein adjacent two crests or bottoms of respective first and second corrugations are separated by a distance (P) which is smaller than the track width (W); characterised in that said corrugations have a height (D) not less than the value of the longest wavelength of said signals recorded on said magnetic medium. An apparatus according to claim 1, wherein the position of said first corrugation (8) is asymmetrically spaced from said second corrugation (8). An apparatus according to claim 1 or claim 2, including a window (7) for a coil winding, wherein the magnetic alloy above said window is thicker than the magnetic alloy below said window. An apparatus according the claim 1 or claim 2, including a window (7) for a coil winding, wherein the length (K) of magnetic alloys (3,4) from the surface of the head to the depth of the gap is shorter than the distance (J) defined between the surface of the head and the lower end of the window for the coil winding. An apparatus according to any preceding claim, wherein a notched groove is formed at each end of said gap to define said track width (W) and said grooves are filled with a non-magnetic material. An apparatus according to claim 4, wherein said non-magnetic material is glass. A method of producing a magnetic head, comprising the steps of: forming a parallel slit-like resist coating film having a pitch smaller than a track width of the magnetic head, on a face of a parallelopipedon-shaped block made of the high permeability ferrite, and subjecting the ferrite block to electrolytic etching within an electrolytic solution to form a corrugation having a height not less than a value of the longest wavelength of luminance signals or colour signals recorded on a tape; providing a layer of a magnetic alloy, such as an amorphous magnetic alloy by sputtering on said corrugation; providing grooves along an edge including the magnetic alloy layer, substantially parallel to said corrugation to define a track having a predetermined width; filing a non-magnetic material in said grooves and polishing said face to form a mirror-like face to thereby provide a first magnetic core portion; preparing a second magnetic core produced in the same manner as in the first magnetic core while providing a groove for a coil winding on face of said magnetic core portion, and providing a gap material of a predetermined thickness on the face of at least one of the first and second magnetic core portions; bonding the first and second magnetic core portions through the gap material so that the track portions abut each other, to thereby form a gap bar having a gap between the first and second magnetic core portions; and, slicing said gap bar at a predetermined angle in relation to the gap. A method according to claim 7, wherein a stepped portion is formed by removing a part of the surface of said parallelopipedon-shaped block and, during said electrolytic etching, a corrugation is formed at said stepped portion.

Inventors: MIYAZAKI, OSAMU, ONO, MITSUAKI, UEDA, MASATAKA
Applicants: MATSUSHITA ELECTRIC INDUSTRIAL CO., LTD.
Application year: 1986
Main classification: G11B5
IPC codes: G11B5