MAGNETIC HEAD OF AMORPHOUS MAGNETIC ALLOY AND PROCESS FOR PRODUCING THE SAME

Abstract: In a magnetic head of amorphous magnetic alloy (4, 4′). The joint parts of magnetic cores (1, 1′) of the magnetic head, or the joint parts and a magnetic gap part (5) are bonded with a bonding glass having a viscosity of 10⁵ poises or less at a temperature by at least 50°C lower than the crystal­ lization temperature of the amorphous magnetic alloy, a good water resistance after sintering and a low coefficient of thermal expansion such as 100 x 10⁻⁷/°C or less. The bonding glass contains 55 to 70% by weight of V₂O₅, 17 to 25% by weight of P₂O₅, 3 to 20% by weight of Sb₂O₃, 0 to 20% by weight of PbO, 0 to 15% by weight of Tl₂O, and 0 to 5% by weight of Nb₂O₅.

Description: This invention relates to a magnetic head of amorphous magnetic alloy with a high performance and to a process for producing such a magnetic head. In the conventional magnetic head, ferrite is used as a magnetic core material, and glass having a working temperature of 600°C or higher has been so far used as an adhesive for bonding magnetic cores or forming a magnetic gap, because of its non-magnetism and matching to the coefficient of thermal expansion of ferrite and moreover because of the required weathering resistance, attrition resistance, strength, etc. With the recent progress of high density recording, a magnetic head with a higher performance that that of the conventional magnetic head has been in demand. An amorphous magnetic alloy with a high saturation magnetic flux density and a high magnetic permeability has been regarded as a promising material for high performance magnetic heads [Japanese Patent Application Kokai (Laid-open) No. 59-180817]. In the case of magnetic cores of amorphous magnetic alloy, it has been impossible to bond the magnetic cores or form a magnetic gap at a higher temperatures than the crystallization temperature of amorphous magnetic alloy, and their practical application has not been realized yet. The crystallization temperature of amorphous magnetic alloy whose saturation magnetic flux density is 8,000 G or higher is as high as about 550°C. The higher the saturation magnetic flux density, the better the recording characteristics, but the lower the crystallization temperature and the less the thermal stability. That is, the magnetic permeability is drastically lowered by crystallization, and the reproducing characteristics are lowered. JP-A-59 146 431 discloses a core blank with an amorphous magnetic alloy layer provided on the joint parts of the magnetic cores, and with an adhesive layer on the magnetic gap surface which is composed of a bonding glass comprising PbO as a main component and which has a melting point of 370°C. An object of the present invention is to provide a magnetic head of amorphous magnetic alloy with distinguished magnetic characteristics. Another object of the present invention is to provide a magnetic head of amorphous magnetic alloy, where magnetic cores are bonded or a magnetic gap is formed with an adhesive incapable of lowering the magnetic properties of an amorphous magnetic alloy. Other objects of the present invention will be apparent from the description which follows. The present inventors have taken notice that the magnetic properties of an amorphous magnetic alloy is in a close relationship with its crystallization temperature and particularly depend upon the heating temperature for bonding magnetic cores of a magnetic head or forming a magnetic gap. Thus, the present inventors have studied by how much a lower temperature than the crystallization temperature would have no adverse effect upon the magnetic characteristics of a magnetic head, and have found that a temperature by at least 50°C lower than the crystallization temperature has no problem. That is, the temperature by 50°C lower than the crystallization temperature is an upper limit to the temperature giving no influence upon the magnetic characteristics. It is during the period of bonding cores or forming a magnetic gap in the production of a magnetic head that the magnetic head is susceptible to the heating giving a most considerable influence upon the magnetic characteristics. Thus, in the case of a magnetic head of amorphous magnetic alloy, it is necessary to use an adhesive capable of bonding at a temperature by at least 50°C lower than the crystallization temperature of the amorphous magnetic alloy in the bonding of the magnetic cores of the formation of the magnetic gap. Furthermore, it is also necessary that the magnetic head is rigid and highly durable, and what is important is that in the production of a magnetic head at least two magnetic cores are bonded together and then the bonded cores are cut to a necessary size. The cutting operation is generally slicing with a diamond cutter while spraying water, etc. onto the bonded cores, and thus it is necessary that the adhesive layer has a good water resistance. During the application of a magnetic head, it is also necessary that the adhesive layer undergoes no deterioration by water, moisture, etc. in the surrounding atmosphere. The present invention is based on such a finding as a result of extensive studies of various adhesive materials that a glass containing V₂O₅ as the main component and also containing P₂O₅ and Sb₂O₃ as defined in claims 1 and 6 provides a distinguished adhesive that can attain the object of the present invention. The V₂O₅-P₂O₅-Sb₂O₃ - based glass is suitable for bonding ferrite cores, because the working temperature is about 460°C, which is comparable to that of head borosilicate (PbO - B₂O₃ - SiO₂ - Al₂O₃) - based glass so far used in the conventional magnetic head [Japanese Patent Application Kokai (Laid-open) No. 59-146431]. Particularly, the coefficient of thermal expansion is as low as 75 x 10⁻⁷/°C. It has been said that a V₂O₅-P₂O₅-based glass has a poor water resistance [Yogyo Kyokai-shi 90 (8), 415 (1982)] and is readily devitrified. However, the water resistance can be improved by adding Sb₂O₃ thereto. As is obvious from Table 3 which follows, the present glass containing 10% by weight of Sb₂O₃ has a water resistance about 20 times as high as that of the lead borosilicate-based glass. Furthermore, the working temperature can be lowered to about 420°C by adding at least one of PbO, Tl₂O, and Nb₂O₅ to the V₂O₅-P₂O₅-Sb₂O₃-based glass, and thus the present invention can provide a magnetic head of amorphous magnetic alloy with distinguished characteristics so far not realized. The composition of the low melting glass containing V₂O₅ as the main component as an adhesive for the magnetic head of amorphous magnetic alloy is 55 to 70% by weight of V₂O₅, 17 to 25% by weight of P₂O₅, 3 to 20% by weight of Sb₂O₃, 0 to 20% by weight of PbO, 0 to 15% by weight of Tl₂O, and 0 to 5% by weight of Nb₂O₅, and a more preferable composition range is 55 to 65% by weight of V₂O₅, 18 to 22% by weight of P₂O₅, 5 to 12% by weight of Sb₂O₃, 3 to 10% by weight of PbO, 3 to 10% by weight of Tl₂O, and 0.5 to 2% by weight of Nb₂O₅, in terms of the oxides stated. As regards the softening point, a PbO-V₂O₅-P₂O₅-based glass has been proposed [Japanese Patent Application Kokai (Laid-open) No. 55-75937], and has a softening point as low as about 320°C owing to a higher PbO content, but has a coefficient of thermal expansion as high as about 150 x 10⁻⁷/°C. Furthermore, PbO attacks the amorphous alloy, and thus the PbO-V₂O₅-P₂O₅-based glass is not suitable as a bonding glass for the magnetic head. In the present adhesive, the working temperature can be lowered by adding PbO thereto, but the amorphous alloy will be attacked with PbO when too much added. On the other hand, Tl₂O can lower the working temperature without such a fear. Nb₂O₅ as added can effectively lower the coefficient of thermal expansion of sintered glass. In the drawings: Fig. 1 is a perspective view showing one embodiment of a magnetic head of amorphous magnetic alloy according to the present invention. Fig. 2 is a perspective view of a core block substrate 1 for Fig. 1. Fig. 3 is an upper side view of the core block with an amorphous magnetic alloy film 4 and a gap spacer 5 . Fig. 4 is a perspective view of the core blocks in an abutted state. Fig. 5 is a perspective view showing another embodiment of a magnetic head of amorphous magnetic alloy according to the present invention. Fig. 6 is a perspective view of a core block for Fig. 5. Fig. 7 is a side view of the core block with a gap spacer. Fig. 8 is a side view of the core blocks in an abutted state. The present invention will be described in detail below, referring to Examples. The saturation magnetic flux density and the crystallization temperature of amorphous magnetic alloys used in Examples are shown in Table 1. As is obvious from Table 1, the higher the saturation magnetic flux density of amorphous magnetic alloy, the lower the crystallization temperature. Thus, bonding of magnetic cores and formation of magnetic gap must be carried out at a lower temperature. Even at a temperature lower than the crystallization temperature, crystallization may take place, if kept at that temperature for a long time. Thus, the present inventors have studied a temperature range in which the crystallization takes place no more even if kept at a given temperature. When an amorphous magnetic alloy starts to undergo crystallization, the magnetic permeability is drastically lowered. Thus, it is necessary to prevent occurrence of crystallization. Before the crystallization of amorphous magnetic alloy is observed by X-ray diffraction or by an electron microscope, the amorphous magnetic alloy undergoes some structural change. Once the structural change occurs, crystallization of the amorphous magnetic alloy slowly proceeds. Detailed behavior from the structural change to the crystallization has not been clarified yet, but the temperature is a most dominant factor. The present inventors have investigated the relationship between the crystallization and the crystallization-promoting temperature to find an allowable range for the heating temperature for producing a magnetic head of amorphous magnetic alloy. Table 2 shows the relationship with the time till the crystallization when the amorphous magnetic alloy is kept at a temperature lower than the crystallization temperature, that is, the retention time, where the state of crystallization is determined by X-ray diffraction. It is obvious from Table 2 that the magnetic characteristics are not practically influenced, if the temperature is by at least 50°C lower than the crystallization temperature of amorphous magnetic alloy. Table 3 shows the compositions and characteristics of low melting glasses used in the bonding of magnetic cores and the formation of a magnetic gap, where No. 1 - No. 6 glasses are melting glasses containing V₂O₅ as the main component and No. 7 and No. 8 glasses are the conventional low melting glasses containing PbO as the main component, which are used as comparative examples. No. 8 glass is one of those workable particularly at a low temperature. The working temperature in Table 3 is a temperature at which the glass shows a viscosity of about 10⁴ poises. A viscosity of at least such a degree is necessary for the bonding of magnetic cores and the formation of a magnetic gap. The water resistance is a weight reduction (mg/g) of a glass piece in a 5x5x5 mm cube, when placed in 40 cc of distilled water and heated at 70°C for 2 hours. The present glasses containing V₂O₅ as the main component have a higher water resistance than the conventional glasses containing PbO as the main component. Furthermore, the present glasses containing V₂O₅ as the main component have a lower coefficient of thermal expansion than the conventional glasses containing PbO. The magnetic heads shown in Fig. 1 are prepared from the amorphous magnetic alloys of Table 1 and the low melting glasses of Table 3 in the following manner. As shown in Fig. 2, a coil groove 2 and track grooves 3 are provided on a substrate 1 to form a magnetic gap surface. For the substrate, ferrite, non-magnetic ceramics or high melting glass is used. Then coefficient of thermal expansion is 80 - 100 x 10⁻⁷/°C. Then, as shown in Fig. 3, an amorphous magnetic alloy film 4 is formed to a thickness of 25 µm on the magnetic gap surface by high frequency sputtering (which will be hereinafter referred to as "RF sputtering"), and then a SiO₂ layer 5 is formed to a thickness of 0.15 µm as a gap spacer thereon by RF sputtering to make the specified gap 0.30 µm distant. Then, as shown in Fig. 4, the core blocks 1,1' with the amorphous magnetic alloy film and the gap spacer are abutted together, and rods 6 composed of a low melting glass of Table 3 are provided and heated up to a temperature at which the glass viscosity reaches 10⁴ poises, and kept at that temperature for 25 minutes to bond the core blocks. Then, the bonded core blocks are ground, polished and cut to prepare a magnetic head shown in Fig. 1. Example 1 Magnetic heads of Fig. 1 were prepared from Co₈₁Nb₁₄Zr₅ as an amorphous magnetic alloy, a high melting glass as a substrate and glasses of Table 3 as bonding glasses for core blocks. The coefficient of thermal expansion of the ZnO-B₂O₃-SiO₂-BaO-based substrate glass used was 80 x 10⁻⁷/°C. The bonding temperature of core blocks, gap of magnetic heads thus prepared and production yield are shown in Table 4. The bonding temperature (working temperature) is a temperature at which the glass has a viscosity of about 10⁴ poises, as already mentioned before. Under the glass bonding conditions, the amorphous magnetic alloy was not crystallized, but in the case of No. 7 and No. 8 glasses containing PbO as the main component, the gap was extended, and was not uniform, and the production yield failed to reach 50%, excluding the peeled magnetic cores and those with cracked adhesive layers. The cause for the extended gap and uneven gap was ready attacking of SiO₂ by the low melting glasses containing PbO as the main component and the resulting intrusion of the glasses into the gap part. The cause for the poor production yield was a large difference between the high melting glass as the substrate and the bonding glasses, and the resulting cracking in the bonding glass part or peeling of core blocks. In the case of No. 1 - No. 6 glasses containing V₂O₅ as the main component, on the other hand, the gap had a specified distance and the production yield was high. The cause for a little lower production yield of No. 2 glass seemed to be a little higher coefficient of thermal expansion of the glass. Example 2 Magnetic heads of Fig. 1 were prepared from Co₈₃Nb₁₃Zr₄ having a lower crystallization temperature than that of Co₈₁Nb₁₄Zr₅ as an amorphous magnetic alloy, monocrystalline (Mn-Zn) ferrite as a substrate, and glasses of Table 3 as a bonding glass. The coefficient of thermal expansion of monocrystalline ferrite used was 95 x 10⁻⁷/°C. Bonding temperature of core blocks, gap of magnetic heads thus prepared and production yield are shown in Table 5. The bonding conditions were the same as in Example 1. Under the glass bonding conditions, no crystallization of other amorphous magnetic alloys than PbO-based No. 7 glass was observed. In the magnetic head using No. 7 glass, the amorphous magnetic alloy was crystallized, and the desired characteristics as a magnetic head were not obtained. In the case of No. 8 glass, the production yield was improved, as compared with that of Example 1, but it was found that the gap was extended and not uniform. Example 3 Magnetic heads of Fig. 1 were prepared from Co 85.5 Nb 11.5 Zr₃ having a lower crystallization temperature than that of Co₈₃Nb₁₃Zr₄ as an amorphous magnetic alloy, a non-magnetic ceramic (2MgO·SiO: forsterite) having a coefficient of thermal expansion of 100 x 10⁻⁷/°C as a substrate, and glasses of Table 3 as a bonding glass for core blocks. Bonding temperature of core blocks, gap of magnetic heads thus prepared and production yield are shown in Table 6. In the case of glasses having a high working temperature, the amorphous magnetic alloy was crystallized, and thus as to No. 1, No. 7 and No. 8 glasses having a high working temperature magnetic heads were prepared at a temperature by about 50°C lower than the crystallization temperature of the amorphous magnetic alloy. As a result, it was found that no strong bonding was obtained, and the production yield was also extremely lowered. In the case of No. 2 - No. 6 glasses containing V₂O₅ as the main component, magnetic heads could be prepared owing to the thoroughly low working temperature without any crystallization of the amorphous magnetic alloy, there the production yield was very high, for example, 90% or higher, and the gap was obtained uniformly as specified. The magnetic heads had a strongly-bonded magnetic gap. Example 4 Magnetic heads of Fig. 1 were prepared from Co₈₇Nb₁₀Zr₃ having a lower crystallization temperature and the highest saturation magnetic flux density in Table 1 as an amorphous magnetic alloy, a BaTiO₃-based non-magnetic ceramics having a coefficient of thermal expansion of 90 x 10⁻⁷/°C as a substrate, and No. 2 - No. 6 glasses of Table 3 as a bonding glass for core blocks. No. 1, No. 7 and No. 8 glasses of Table 3 were not used owing to their too high working temperatures for the amorphous magnetic alloy of Co₈₇Nb₁₀Zr₃. In Table 7, bonding temperature of core blocks with No. 2 - No. 6 glasses, gap of the thus prepared magnetic heads and production yield are shown. In the case of No. 2 and No. 5 glasses, the amorphous magnetic alloy was crystallized, and could not be used for a magnetic head, whereas in the case of No. 3, No. 4 and No. 6 glasses, magnetic heads could be prepared with a higher production yield than 90% and a specified gap without crystallization of the amorphous magnetic alloy. The magnetic heads shown in Fig. 5 are prepared in the following manner. As shown in Fig. 6, an amorphous magnetic alloy film 7 is sandwiched between non-magnetic reinforcing members 8 , 9 to form a core block in a sandwich structure. After provision of coil grooves 10 , the magnetic gap surfaces 11 are polished. For the reinforcing members 8 , 9 , a non-magnetic ceramics or high melting glass is used. Then, a gap spacer corresponding to a gap is formed on the magnetic gap surface 11 so as to make a gap 0.26 µm distant by forming a SiO₂ layer at first to a thickness of 0.10 µm on the magnetic gap surface 11 by RF sputtering and then a low melting glass layer 13 of Table 3 to a thickness of 0.03 µm thereon by RF sputtering, as shown in Fig. 7. Then, the thus prepared core blocks are abutted together, as shown in Fig. 8, and a glass rod 14 having the same composition as that of the glass layer 13 is provided in the core groove 10 and heated to a temperature at which the glass has a viscosity of about 10⁵ poises and kept at that temperature for 18 minutes to bond the core blocks together. Then, the bonded blocks are ground, polished and cut to prepare a magnetic head shown in Fig. 5. In bonding core blocks, it is not necessary to fill a low melting glass even into the track groove exactly as in the magnetic head shown in Fig. 1, and thus a glass viscosity of about 10⁵ poises is satisfactory. The magnetic head of Fig. 5 has such an advantage as workable at a lower temperature than in the case of the magnetic head shown in Fig. 1. Example 5 Magnetic heads of Fig. 5 were prepared from Co₈₃Nb₁₃Zr₄ as an amorphous magnetic alloy, a SiO₂-PbO-K₂O-ZnO-based high melting glass having a coefficient of thermal expansion of 90 x 10⁻⁷/°C as a reinforcing member, and glasses of Table 3 as a bonding glass for core blocks. Bonding temperature of core blocks, gap of the thus prepared magnetic heads and production yield are shown in Table 8 Under the glass bonding conditions the amorphous magnetic alloy was not crystallized. In the case of No. 7 and No. 8 glasses containing PbO as the main component, the gap extension and the uniformity were obtained as specified, as in the magnetic head shown in Fig. 1, but the production yield was low and no strongly bonded magnetic gap was obtained, because it seems that the attack of the magnetic gap part of glass containing PbO as the main component by SiO₂ owing to such a lower temperature than the working temperature that the glass viscosity was 10⁵ poises. In the case of No. 1 - No. 6 glasses containing V₂O₅ as the main component, on the other hand, the gap was obtained as specified with high production yields, particularly higher than 90% with respect to No. 3 - No. 6 glasses. Furthermore, strongly bonded magnetic gaps were obtained. Example 6 Magnetic heads of Fig. 5 were prepared from Co₈₇Nb₁₀Zr₃ as an amorphous magnetic alloy, a CaTiO₃-based non-magnetic ceramics having a coefficient of thermal expansion of 100 x 10⁻⁷/°C as a substrate, and No. 2 - No. 6 and No. 8 glasses of Table 2 as a low melting glass for bonding core blocks. No. 1 and No. 7 glasses of Table 2 had too high a bonding temperature for the amorphous magnetic alloy of Co₈₇Nb₁₀Zr₃. Bonding temperature for core blocks using the glasses, gap of the thus prepared magnetic head, and production yield are shown in Table 9. From the glasses, the specified gap was obtained, but in the case of No. 8 glass containing PbO as the main component the amorphous magnetic alloy was crystallized, and the resulting magnetic head was not practically applicable. In the case of No. 2 - No. 6 glasses, core blocks could be strongly bonded together without crystallization of the amorphous magnetic alloy, and the magnetic head could be prepared with high yields of 90% or more. Example 7 An amorphous magnetic alloy film was formed on the same magnetic core blocks as in Example 5 in the same manner as in Example 5, and then a 10% solution of a polyimide-based resin Ultem (trademark of a product made by General Electric, USA) in dimethylformamide was spin coated thereon in place of the SiO₂ spacer of Example 5, and predried at 250°C for 30 minutes to remove the solvent therefrom. Then, the core blocks were abutted together, and heated at 300°C for 30 minutes to bond them together. After the bonding, the bonded core blocks were cut to prepare a magnetic head of amorphous magnetic alloy. The thus prepared head had a strongly bonded magnetic gap, and had no crystallization at all because of the low heating temperature. The polyimide-based resin had a high bonding force and thus was very advantageous for bonding such a thin layer. The present invention can provide a magnetic head of amorphous magnetic alloy with a high performance based on strongly bonded magnetic cores and a precise magnetic gap without lowering the characteristics of amorphous magnetic alloy.

Claims: A magnetic head having magnetic cores counterposed with a small magnetic gap between them and comprising core members (1,1';8,9,8',9') with amorphous magnetic alloy layers (4,4';7,7'), characterised in that a joint part of the magnetic cores, and optionally also an adhesive layer at the magnetic gap (5), is composed of a bonding glass which contains V, P, Sb, and optionally Pb, Tl and Nb in the following proportions by weight in terms of the oxides: 55 to 70% V₂O₅ 17 to 25% P₂O₅ 3 to 20% Sb₂O₃ 0 to 20% PbO 0 to 15% Tl₂O and 0 to 5% Nb₂O₅. A magnetic head according to claim 1 in which the bonding glass has a viscosity of 10⁵ poises or less, at or below a temperature 50°C below the crystallisation temperature of the amorphous magnetic alloy. A magnetic head according to claim 1 or claim 2 wherein the proportions in terms of the oxides are 55 to 65% V₂O₅ 18 to 22% P₂O₅ 5 to 12% Sb₂O₃ 3 to 10% PbO 3 to 10% Tl₂O and 0.5 to 2% Nb₂O₅ A magnetic head according to claim 3 in which the bonding glass has a coefficient of thermal expansion of from 70 to 100 x 10⁻⁷/°C. A magnetic head according to any one of the preceding claims in which the amorphous magnetic alloy is based on Co-Nb-Zr as main components. A process for producing a magnetic head using amorphous magnetic alloy and having magnetic cores counterposed with a small magnetic gap between them, comprising forming the cores of core members (1,1';8,9,8',9') with amorphous magnetic alloy layers (4,4';7,7'), and characterised by bonding joint parts of the magnetic cores, optionally also the magnetic gap part (5), with a bonding glass which contains V, P, Sb, and optionally Pb, Tl and Nb in the following proportions by weight in terms of the oxides: 55 to 70% V₂O₅ 17 to 25% P₂O₅ 3 to 20% Sb₂O₃ 0 to 20% PbO 0 to 15% Tl₂O and 0 to 5% Nb₂O₅. A process according to claim 6 in which the bonding glass achieves a viscosity of 10⁵ poise or less, below a temperature 50°C below the crystallisation temperature of the amorphous magnetic alloy. A process according to claim 6 or claim 7 in which the bonding glass is as defined in claim 3. A process according to any one of claims 6 to 8 in which the amorphous magnetic alloy is an alloy of Co-Nb-Zr as main components.

Inventors: MORIKAWA, JUICHI, NAITOH, TAKASHI, NAMEKAWA, TAKASHI, OGIHARA, SATORU, YAMADA, SEIICHI
Applicants: HITACHI, LTD.
Application year: 1986
Main classification: G11B5
IPC codes: C22C45, G11B5, C03C8