Substrate material for magnetic head and magnetic head using same

Abstract: A substrate material for a magnetic head, which comprises an oxide composed mainly of WO₃ and has a thermal expansion coefficient of 100 to 130 × 10⁻⁷/°C, and a magnetic head using the substrate material.

Description: This invention relates to a substrate material for a magnetic head and a magnetic head using it. Ferrite has conventionally been widely used as a core material for a magnetic head due to its excellent machinability and wear resistance. However, its magnetic saturation is lower than alloy materials by 30 to 50 percent. Therefore, when ferrite is used as a core material in a head to be used with high-density recording tapes having a high abrading force, which have been developed in recent years, the low magnetic saturation of the ferrite head core material presents a problem, and the ferrite head has a poor S/N compared with metal heads, since noise due to rubbing is caused during tape running. From the above viewpoint, Sendust and amorphous metal magnetic materials are used as a core material in a head for use with high density recording media. A head using a magnetic metal material with a so-called sandwich structure is shown in Fig. 3, in which a magnetic metal 4 of a tape-running surface having a gap 5 is placed between nonmagnetic substrate materials 3. In this case, the nonmagnetic substrate material is made of crystallization glass. The problem in this case is the partial abrasion which occurs between a substrate 1 and a magnetic metal material 2 when a tape runs, as is schematically shown in Fig. 4. That is, the magnetic material suffers partial abrasion relative to the substrate, and hence head output decreases due to spacing loss. For this reason, characteristics of the substrate and magnetic metal materials such as coefficient of thermal expansion, etc., are required to be in agreement. In order to overcome such a problem, calcium titanate (CaTiO₃)-based ceramic materials have been proposed as a substrate material for a magnetic head for use with high-density recording media, a metal evaporated tape in particular. However, a ceramic substrate formed from such a material has very poor machinability. For example, the rate for cutting it with a diamond cutter is as poor as 1/5 to 1/10 of that for cutting a ferrite material, and so mass-production of magnetic heads therefrom has been difficult. A magnetic head having a so-called sandwich structure of a magnetic material between non-magnetic substrate material is described in EP-A-86 103 255.5 (publication number: EP-A-194650) in which the thermal expansion coefficient of the substrate material is equal or near that of the magnetic material. However, this magnetic head has a magnetic core formed of a soft magnetic material and a substrate for supporting the core mainly consisting of α - Fe₂O₃. It is an object of this invention to provide a substrate material for a magnetic head having a so-called sandwich structure of a magnetic metal material between nonmagnetic substrate material, which suffers little partial abrasion between the substrate and the magnetic metal material when a tape runs, or is free from decrease in head output caused by spacing loss when the magnetic material suffers partial abrasion relative to the substrate, and which has excellent machinability; and a magnetic head using said substrate material. According to one aspect of this invention, there is provided a substrate material for a magnetic head, characterised in that it comprises 70 to 91 mol% of WO₃ and 9 to 30 mol% of Fe₂O₃. According to a second aspect of this invention, there is provided a substrate material for a magnetic head, characterised in that it comprises 85 to 95 mol% of WO₃ and 5 to 15 mol% of Cr₂O₃. According to a further aspect of this invention, there is provided a magnetic head characterised in that at least a surface thereof which is to be in contact with a running magnetic tape comprises a magnetic material sandwiched between substrates, wherein the material of the substrates comprises 70 to 91 mol% of WO₃ and 9 to 30 mol% of Fe₂O₃. According to yet a further aspect of this invention, there is provided a magnetic head characterised in that at least a surface thereof which is to be in contact with a running magnetic tape comprises a magnetic material sandwiched between substrates wherein the material of the substrates comprises 85 to 95 mol% of WO₃ and 5 to 15 mol% of Cr₂O₃. In this invention, since the thermal expansion coefficient a of the substrate is in agreement with that of the metal magnetic material (amorphous alloy: α ≈ 115 x 10⁻⁷/°C, Sendust alloy: α ≈ 130 x 10⁻⁷/°C, Permalloy: α ≈ 120 x 10⁻⁷/°C), a magnetic film can be formed by using a thin film forming apparatus, and the film is almost as easily machinable as Mn-Zn ferrite. A magnetic head using it as a substrate suffers little partial abrasion between the substrate and an alloy magnetic material when a tape runs thereon. Hence, the head is free from decrease in output and gives a stable output. Fig. 1 is a front view of a tape-running surface of a magnetic head in accordance with an embodiment of the invention. Fig. 2 is a side view thereof. Fig. 3 is a front view of a tape-running surface of a conventional magnetic head. Fig. 4 is a side view of a tape-running surface of a conventional magnetic head. Embodiments of this invention will be explained hereinbelow by reference to drawings. Example 1 WO₃ and Fe₂O₃ or Cr₂O₃ were weighed out so as to form a composition as shown in Table 1, and the composition was wet-mixed in a ball mill for 16 hours and dried. Then, the mixture was calcined in air at 800°C for 1 hour, and it was again wet-mixed in a ball mill for 16 hours and then dried. Thereafter, water was added as a binder, and the mixture was molded by using a mold with an hydraulic press at 500 kg/cm². Then, the compact was press-sintered by holding it in air at 950°C to 1,100°C for 2 hours under a pressure of 300 kg/cm². Substrate Thermal expansion coefficient α 10⁻⁷/°C Machinability No WO₃ Fe₂O₃ Cr₂O₃ 1 95 5 - 140 1.1 2 91 9 - 130 0.9 3 80 20 - 108 1.1 4 70 30 - 100 1.3 5 60 40 - 95 1.6 6 97 - 3 138 1.0 7 95 - 5 130 1.0 8 90 - 10 108 1.2 9 85 - 15 100 1.5 10 80 - 20 90 1.8 Conventional example CaTiO₃ 108 5.0 Table 1 shows thermal expansion coefficients of sintered materials produced as above. Load currents of a spindle motor required for cutting these sintered materials, which have the same dimensions as a ferrite core, are shown in Table 1 as machinability and the value is normalised with that required for cutting a ferrite core. All of the materials exhibited a smaller cutting load than the material of calcium titanate (CaTiO₃), and could be easily cut or exhibited machinability similar to that of a ferrite core. EXAMPLE 2 Another embodiment of this invention is explained by reference to Figs. 1 and 2, in which 6, 6', 9 and 9' each indicate a substrate, 7 and 7' each indicate an amorphous alloy film, 8 and 8' each indicate a bonding glass layer, 10 indicates a winding aperture, 11 indicates a bonding glass, and 12 indicates a gap. A substrate 6 was formed by specularly polishing a sintered body having substrate material composition as shown in Table 1 and fully washing it. A vacuum chamber was evacuated to 3 x 10⁻⁷ Torr, and then, an Ar gas was introduced until the pressure inside the chamber was 2 x 10⁻² Torr. Co₈₁Nb₁₃Zr₆ as a target composition was sputtered to form an amorphous alloy film 7 having a thickness of 30 µ. Separately, a substrate 9 of which the material composition was the same as that of the substrate 6 was bonded through a bonding glass layer 8 to form a core. Then, a winding aperture 10 was made in a gap-facing surface, and the facing surface was specularly polished with a diamond paste. Thereafter, SiO₂ as a gap spacer material was sputtered on the surface in a predetermined thickness, whereby one block for gap formation was completed. A laminated core half-body having the same structure, composed of 6' to 9', as that of the above block, was combined with said block and a gap was formed by using a bonding glass 11. A head was taken from a bar comprising a pair of these two blocks, and completed. As a comparative example, a head using a crystallization glass as a substrate was also prepared. Each of the heads of this invention prepared as above and the head as the comparative example was set in a video tape recorder (head/tape relative velocity 3.8 mm/second), and a tape running test was carried out by using a metal evaporated tape. When the head using a crystallization glass was used, a great decrease in head output was observed, whereas the heads using the material of this invention as a substrate showed a stable output. Table 2 shows a partial abrasion between the substrate and the magnetic metal material (as an abrasion depth difference between the substrate and metal magnetic material) after the metal evaporated tape was run for 100 hours. In addition, the head output remains at the value as when the initial value is 0 dB. Substrate Material Partial abrasion (A) Output (dB) WO₃₋Fe₂O₃ 50 -0.2 WO₃₋Cr₂O₃ 70 -0.5 Crystallization glass 200 -2.5 The compositions of the substrate materials shown in Table 2 are not defined. However, almost like results were obtained when the substrate materials were as those which are recited in the appended claims In this invention, the composition of the substrate material is limited to 70 to 91 mol% of WO₃ and 9 to 30 mol% of Fe₂O₃ or 85 to 95 mol% of WO₃ and 5 to 15 mol% of Cr₂O₃ for the following reason. If the composition is outside the above ranges, the thermal expansion coefficient of the substrate material becomes more than 130 x 10⁻⁷/°C or less than 100 x 10⁻⁷/°C, and when an amorphous alloy is deposited by using a sputtering apparatus, etc., there is a risk of the alloy film being peeled from the substrates. The substrate material may contain some other oxides and in some cases, nitrides and carbides to the extend of several percent so long as the thermal expansion coefficient α remains in the range 100 to 130 x 10⁻⁷/°C and machinability thereof does not deteriorate. Further, not only an amorphous alloy film of a metal-metal system such as Co-M (M denotes a metal such as Nb, Ti, Ta, Zr, W or the like) or Co-M'-M'' (M' and M'' each denote a metal as defined for the above M) is usable, but also an amorphous alloy film of a metal-metalloid system containing Si, B, C or P is also usable without any special problem. In addition, the above embodiments have discussed magnetic metal materials having a mono-layer head core. However, laminated cores composed alternatively of magnetic material(s) and interlayer insulating material(s) also have a similar effect. Further, the same effect is obtained even when the amorphous alloy film is substituted with Sendust (Fe-Si-Al) alloy film. In that case the composition of Sendust alloy is not critical to obtain the effect. This also is the case for the substitution of the amorphous alloy film with a permalloy alloy film wherein a like effect can be obtained. As discussed above, this invention uses a ceramic material of an oxide composed mainly of WO₃ in a magnetic head. Therefore, the ceramic material has better machinability than a conventional material of calcium titanate (CaTiO₃), and hence, has excellent machinability. A magnetic head using it as a substrate material has nearly the same thermal expansion coefficient as that of an amorphous alloy. Thus, there is no peeling problem as with an amorphous alloy film from the substrates even if it is formed by using a sputtering apparatus. Further, with a magnetic head having a sandwich structure in which a magnetic metal material is placed between nonmagnetic substrate materials, the magnetic head of this invention suffers less partial abrasion between the substrate and the magnetic metal material than a magnetic head using a crystallization glass. That is, the magnetic head of this invention is free from decrease in head output caused by spacing loss or a dent of the magnetic material relative to the substrate. Therefore, a stable output can be obtained, and highly reliable magnetic heads can be provided.

Claims: A substrate material for a magnetic head, characterised in that it comprises 70 to 91 mol% of WO₃ and 9 to 30 mol% of Fe₂O₃. A substrate material for a magnetic head, characterised in that it comprises 85 to 95 mol% of WO₃ and 5 to 15 mol% of Cr₂O₃. A magnetic head characterised in that at least a surface thereof which is to be in contact with a running magnetic tape comprises a magnetic material (7, 7') sandwiched between substrates (6, 6', 9, 9') wherein the material of the substrates comprises 70 to 91 mol% of WO₃ and 9 to 30 mol% of Fe₂O₃. A magnetic head characterised in that at least a surface thereof which is to be in contact with a running magnetic tape comprises a magnetic material (7, 7') sandwiched between substrates (6, 6', 9, 9') wherein the material of the substrates comprises 85 to 95 mol% of WO₃ and 5 to 15 mol% of Cr₂O₃. A magnetic head according to claim 4, characterised in that the magnetic substance (7, 7') comprises an amorphous alloy. A magnetic head according to claim 4, characterised in that the magnetic substance (7, 7') comprises a Sendust alloy or a Permalloy.

Inventors: HIROTA KEN, KUGIMIYA KOICHI, SATOMI MITSUO, HIROTA, KEN, KUGIMIYA, KOICHI, SATOMI, MITSUO
Applicants: MATSUSHITA ELECTRIC IND CO LTD, MATSUSHITA ELECTRIC INDUSTRIAL CO., LTD.
Application year: 1990
Main classification: G11B5
IPC codes: G11B5, H01F10