JP2005247602A - Glass composition and magnetic head - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a glass composition which is hardly crystallized even in a heat-treatment process in sealing and to provide a magnetic head. <P>SOLUTION: The glass composition has a composition containing, by mass % of oxide basis, 20-70% Bi<SB>2</SB>O<SB>3</SB>, 5-25% B<SB>2</SB>O<SB>3</SB>, 1-23% SiO<SB>2</SB>, 0.5-20% ZnO, 0.1-10% Al<SB>2</SB>O<SB>3</SB>, 0-30% SrO, 0-35% CaO, 0-5% TiO<SB>2</SB>, 0-5% La<SB>2</SB>O<SB>3</SB>, 0-5% Y<SB>2</SB>O<SB>3</SB>, 0-5% Fe<SB>2</SB>O<SB>3</SB>, 0-5% MnO, and 0-5% R<SB>2</SB>O (wherein, R<SB>2</SB>O is at least one kind selected from Li<SB>2</SB>O, Na<SB>2</SB>O, K<SB>2</SB>O, and Cs<SB>2</SB>O). <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a glass composition that can be used for glass for a magnetic head constituting a magnetic head, and a magnetic head suitable for recording / reproducing magnetic information on / from a magnetic recording medium.

  In general, a magnetic head is obtained by providing a very narrow gap (magnetic gap) in a ring-shaped magnetic material wound with a coil. The magnetic gap part of the magnetic head is composed of a magnetic material having a gap and a nonmagnetic material filled in the gap. In a magnetic head for a video tape recorder and a floppy disk, an oxide material such as Mn—Zn ferrite having excellent magnetic properties, wear resistance, machinability and the like is mainly used as a magnetic material. In order to improve the performance of the magnetic head, a material in which a metal ferromagnetic film such as Sendust alloy or Co-based amorphous alloy is arranged in the magnetic gap portion is also used.

  As a method of forming a magnetic gap, a nonmagnetic gap material is formed on the surface of a magnetic material in a thin film by sputtering or vapor deposition to form a pair of magnetic core halves, and the pair of magnetic core halves, There is a method in which a gap material is used for sealing and sealing with glass. The glass used for this sealing needs to satisfy the following characteristics. Since the strain generated in the magnetic material due to heat bonding between the glass and the magnetic material is closely related to the electromagnetic conversion characteristics of the magnetic head, the thermal expansion coefficient of the glass is close to that of the magnetic material. Do not react with magnetic materials. The glass is stable and does not crystallize in the heat treatment process. Excellent chemical weather resistance that is not affected by water, polishing liquid or cleaning liquid used in the head manufacturing process.

In response to these requirements, PbO—SiO ₂ —ZnO, PbO—B ₂ O ₃ , PbO—SiO ₂ —R ₂ O (R ₂ O is Li ₂ O, Na ₂ O, K ₂ O), etc. It has been used (for example, see Patent Document 1).

However, in recent years, environmental problems have been pointed out with respect to PbO-containing glass, and in order to solve this problem, a Bi ₂ O ₃ —B ₂ O ₃ —RO-based low melting point glass not containing PbO has been developed. (See, for example, Patent Document 2)

Japanese Patent Laid-Open No. 5-105478 Japanese Patent Laid-Open No. 9-278483

However, such Bi ₂ O ₃ -based low-melting-point glass tends to react with the magnetic material or to be crystallized by heat treatment during sealing of the magnetic head. Thus, when the glass reacts with the magnetic material during sealing, the magnetic properties of the magnetic material change, and when crystallized, the strain generated in the magnetic material changes due to the heat-bonding between the glass and the magnetic material, and the magnetic head electromagnetic Conversion characteristics deteriorate. Therefore, the Bi ₂ O ₃ low melting point glass has a problem that it cannot be used as a sealing glass for a magnetic head. Further, Patent Document 2 has a problem that although it is optional, it can contain a large amount of BaO, and harmful water-soluble BaO is eluted.

  Accordingly, the present invention relates to a sealing glass for a magnetic head, and provides a glass composition and a magnetic head that are less likely to react with a magnetic material even in a heat treatment step during sealing, are less likely to crystallize, and have no BaO elution. Objective.

In order to solve the above problems, the present inventor has paid attention to oxides such as Bi ₂ O ₃ , ZnO, SiO ₂ , B ₂ O _3, etc. It has been found that the glass composition is less likely to react and less crystallize, and has other characteristics. Other properties are the coefficient of thermal expansion and chemical weather resistance.

The glass composition of the present invention corresponding to claim 1 of the present invention is expressed in terms of mass% based on oxide, Bi ₂ O ₃ : 20 to 70%, B ₂ O ₃ : 5 to 25%, SiO ₂ : 1 to 1. _{23%, ZnO: 0.5~20%,} Al 2 O 3: 0.1~10%, SrO: 0~30%, CaO: 0~35%, TiO 2: 0~5%, La 2 O 3 _{: 0~5%, Y 2 O 3} : 0~5%, Fe 2 O 3: 0~5%, MnO: 0~5%, R 2 O: 0~5% (R 2 O: Li 2 O, It has a composition of at least one selected from Na ₂ O, K ₂ O, and Cs ₂ O).

The glass composition of the present invention corresponding to claim 2 is Bi ₂ O ₃ : 40 to 55%, B ₂ O ₃ : 10 to 20%, SiO ₂ : 1 to 10% in terms of mass% based on oxide. _{ZnO: 5~18%, Al 2 O} 3: 0.5~5%, SrO: 10~20%, CaO: 0~10%, TiO 2: 0~2%, La 2 O 3: 0~2% , Y ₂ O ₃ : 0 to 2%, Fe ₂ O ₃ : 0 to 2%, MnO: 0 to 2%, R ₂ O: 0 to 3% (R ₂ O: Li ₂ O, Na ₂ O, K ₂ O and at least one selected from Cs ₂ O).

The invention corresponding to claim 3 is the glass composition corresponding to claim 1 or 2, wherein the thermal expansion coefficient is 85 to 140 × 10 ⁻⁷ / ° C.

  The magnetic head of the present invention corresponding to claim 4 is a magnetic head in which a winding groove is provided in at least one of a pair of magnetic core halves, and the pair of magnetic cores are joined with a gap portion, The pair of magnetic core halves are bonded with the glass composition according to any one of claims 1 to 3.

As described above, the glass composition of the present invention is bismuth borosilicate glass that does not contain PbO as a main component, has a thermal expansion coefficient of 85 to 140 × 10 ⁻⁷ / ° C., and is sealed by heat treatment at 550 ° C. to 750 ° C. It has the chemical weather resistance equivalent to that of the lead glass composition, and has the effect of being hardly crystallized and hardly reacting with the magnetic material in the heat treatment process at the time of sealing.

  In addition, the magnetic head of the present invention has an effect of providing a magnetic head excellent in electromagnetic conversion characteristics because it is difficult to crystallize even in a heat treatment process during manufacturing and the residual stress due to heating is constant.

  Hereinafter, the glass composition (example of the glass composition which concerns on Claims 1-3) of the Example of this invention is demonstrated. In Table 1, each composition of the glass compositions of Examples 1 to 11 of the present invention and the glass compositions of Comparative Examples 1 and 2, melting conditions, glass transition temperature, glass softening temperature, thermal expansion coefficient, Describes chemical weather resistance, glass stability, and reactivity with ferrite. The glass compositions of Examples 1 to 11 and the glass compositions of Comparative Examples 1 and 2 are glass compositions for magnetic heads. In the chemical weather resistance, glass stability, and ferrite reactivity columns, ○ when the magnetic head material is good, x when the magnetic head material cannot be used, and △ when it is not so good but usable. Is displayed. As for the glass composition of the comparative example 2, the reactivity column with a ferrite was x.

The glass composition for a magnetic head of the present invention is expressed in terms of mass% based on oxide, Bi ₂ O ₃ : 20 to 70%, B ₂ O ₃ : 5 to 25%, SiO ₂ : 1 to 23%, ZnO: _{0.5~20%, Al 2 O 3:} 0.1~10%, SrO: 0~30%, CaO: 0~35%, TiO 2: 0~5%, La 2 O 3: 0~5% , Y ₂ O ₃ : 0 to 5%, Fe ₂ O ₃ : 0 to 5%, MnO: 0 to 5%, R ₂ O: 0 to 5% (R ₂ O: Li ₂ O, Na ₂ O, K ₂ O and at least one selected from Cs ₂ O).

Furthermore, in order to adjust the viscosity and thermal expansion coefficient of the glass, _MgO in a range of _{0~5%, BaO, ZrO 2,} NiO, Nb 2 O 5, MoO 3, WO 3, TeO 2, Ag 2 O, etc. Can be added. Then, the raw materials are prepared so as to have the above composition, and the batch raw materials are put into a platinum crucible and heated and melted in an electric furnace at 1100 to 1400 ° C. for 1 to 3 hours. The glass block was obtained by pouring upward. After this glass block is cooled, it is cut and polished to form a glass rod or square bar with a predetermined shape, or after the glass block after cooling is cut, it is redrawn into a glass rod or square bar with a predetermined shape. Mold.

  As described above, (Table 1) shows an example of the glass composition according to claims 1, 2 and 3 of the present invention. The reason why the range of the content of each component is limited as described above will be described in detail in Examples.

  In addition, about components other than the structural component in the above glass composition, it can add for a certain kind of modification | change in the range which does not impair the effect of this invention.

  Hereinafter, although embodiment of the glass composition of this invention is described, this invention is not limited by these.

As described in Example 1 of Table 1, Bi ₂ O ₃ : 46%, B ₂ O ₃ : 14%, SiO ₂ : 5%, ZnO: 13%, Al ₂ O ₃ : 2%, SrO : 14%, CaO: 4%, TiO ₂ : 1.5%, Na ₂ O: 0.5%. The batch raw material was put in a platinum crucible and heated and melted in an electric furnace at 1250 ° C. for 2 hours, and then poured onto an iron plate to form a glass block, which was then cooled overnight.

  The properties of the glass thus obtained were measured as follows. Glass transition point and softening point: A part of the glass block was cut out, and this glass lump was made into powder of 100 mesh or less. And when each temperature was measured with the temperature increase rate of 10 degree-C / min using the differential thermal analyzer, they were the transition point 471 degreeC and the softening point 544 degreeC. Since the softening point is 544 ° C., the heat treatment temperature at the time of actual sealing is about 654 ° C., so that the sealing can be performed without deteriorating the magnetic properties of the magnetic material.

Thermal expansion factor: When the glass block was cut out to a size of 5φ × 20 mm, the average thermal expansion coefficient from 30 to 300 was measured at a heating rate of 10 ° C./min using a differential dilatometer. It was 95 × 10 ⁻⁷ / ° C. Therefore, this glass can be used for sealing a magnetic material having a thermal expansion coefficient of 90 to 100 × 10 ⁻⁷ / ° C.

  Chemical weather resistance: The one cut out from the glass block was processed into a size of 10 × 10 × 10 mm, and the entire surface was mirror-finished. And after immersing in 95 degreeC distilled water for 1 hour, the presence or absence of the discoloration of the glass surface was determined with the naked eye. As a result, no discoloration was observed on the glass surface, and it had excellent chemical durability. Therefore, after sealing the magnetic material, the glass part is not eroded even if a process such as polishing is performed, so that there is a step in the sliding part of the head, or elution deposits adhere to the head, thereby functioning the head. There is no damage.

  Glass stability: Cut out from glass block, molded into 0.5 × 0.5 × 30 mm glass rod, heat-treated at 750 ° C. for 1 hour while placed on alumina substrate, and cooled to room temperature The glass surface was observed with a 50 × optical microscope. As a result, no precipitation of crystals was observed. Therefore, it is possible to prevent a decrease in sealing strength due to crystal precipitation and a change in the thermal expansion coefficient. As described above, the glass itself can be sufficiently sealed by heat treatment at about 650 ° C., but in this evaluation, the glass was evaluated at a high temperature that does not cause deterioration of the magnetic properties of the magnetic material.

  Reactivity with ferrite: Cut out from glass block, processed to 3 × 3 × 10 mm size, and placed on single-crystal ferrite finished in mirror surface, softening point + 100 ° C. for 1 hour The heat treatment was performed. Then, after cooling to room temperature, the cross section of glass and ferrite was polished and the interface was observed with a 500 times optical microscope. As a result, no corrosion occurred on the ferrite surface due to the reaction with glass. Therefore, even if sealing is performed using this glass, the magnetic properties of the magnetic material do not deteriorate.

  As described in Examples 2 to 11 in Table 1, the raw materials were mixed to form a batch raw material with a platinum crucible and melted under the melting conditions described in Table 1, and then, as in Example 1, After casting on an iron plate to form a glass block, it was cooled overnight.

  And when the sample for characteristic evaluation was created from this glass block similarly to the said Example 1, and it evaluated, the glass transition point was 420-546 degreeC and the softening point became 510-616 degreeC. Accordingly, the heat treatment temperature is about 610 to 716 ° C., and sealing can be performed without deteriorating the magnetic properties of the magnetic material.

The thermal expansion coefficient is 85 to 137 × 10 ⁻⁷ / ° C., and can be used for sealing magnetic materials having a thermal expansion coefficient of 80 to 142 × 10 ⁻⁷ / ° C.

  In the evaluation of chemical weather resistance, none of the samples showed any discoloration on the glass surface, and the function of the head was impaired even if these glasses were used to seal the magnetic material as in Example 1. There is no.

  In the evaluation of the glass stability, all samples were observed with a 50 × optical microscope, but no crystals were precipitated. Therefore, even if the magnetic material is sealed using these glasses, the sealing strength is not lowered and the function of the head is not impaired.

  In the evaluation of reactivity with ferrite, the interface between the glass and ferrite of all the samples was observed with a 500-fold optical microscope, but no erosion due to reaction with the glass occurred on the ferrite surface. Therefore, even if a magnetic material is sealed using these glasses, the magnetic properties are not deteriorated.

Comparative Example 1 is an example of PbO—SiO ₂ —ZnO-based glass. Comparative Example 2 is a Bi ₂ O ₃ —B ₂ O ₃ —R ₂ O-based glass and contains a total content of alkali metal oxides as large as 6%. As can be seen from this comparative example, when a large amount of alkali metal oxide is contained in the glass composition for a magnetic head, in the evaluation of the stability of the glass, crystals are precipitated on the glass surface. It was in an unusable state.

Here, the reason for limitation of each component which comprises this invention is shown below. Bi ₂ O ₃ is a main component of the glass composition and has an effect of lowering the softening point. The content is 20 to 70% (hereinafter, “%” means “% by mass” unless otherwise specified), preferably 40 to 55%. If the content of Bi ₂ O ₃ exceeds 70%, it becomes easy to crystallize during heat treatment and a stable glass cannot be obtained, and if it is less than 20%, the softening temperature becomes high and firing at a predetermined working temperature becomes difficult.

B ₂ O ₃ is an essential component of the glass composition as a glass forming component, and its content is 5 to 25%, preferably 10 to 20%. When the content of B ₂ O ₃ exceeds 25%, the softening temperature of the glass becomes high, and baking at a predetermined temperature becomes difficult, and further, the chemical weather resistance becomes worse. On the other hand, if it is less than 5%, the glass becomes unstable and tends to devitrify.

SiO ₂ has an effect of suppressing the reaction with the magnetic material and an improvement in the chemical durability of the glass. Its content is 1 to 23%, preferably 1 to 10%. When the content exceeds 23%, the softening temperature becomes high, and firing at a predetermined temperature becomes difficult. If it is less than 1%, the effect of suppressing the reaction with the magnetic material and the improvement of the chemical durability of the glass are lost. Glass becomes unstable and easily crystallizes.

  ZnO is effective in stabilizing the glass, and its content can be added to 0.5 to 20%, preferably 5 to 18%. If the ZnO content exceeds 20%, crystallization is likely to occur and a stable glass cannot be obtained. If it is less than 0.5%, there is no effect in stabilizing the glass.

Al ₂ O ₃ is effective for improving and stabilizing the chemical durability of the glass, and its content can be added to 0.1 to 10%, preferably 0.5 to 5%. However, if it exceeds 10%, the softening temperature becomes high and firing at a temperature of 550 to 750 ° C. becomes difficult. If it is less than 0.1%, there is no effect in improving and stabilizing the chemical durability of the glass.

  Although SrO is not an essential component, it is effective for stabilizing the glass, and its content is up to 30%, preferably 10 to 20%. If the SrO content exceeds 30%, crystallization is likely to occur and a stable glass cannot be obtained.

  CaO is not an essential component but has an effect of improving the chemical weather resistance of the glass, and its content is up to 35%, preferably up to 10%. When the content of CaO exceeds 35%, crystallization is facilitated and a stable glass cannot be obtained.

TiO ₂ is not an essential component, but has an effect of improving the chemical weather resistance of the glass, and its content is up to 5%, preferably up to 2%. If the content of TiO ₂ exceeds 5%, crystallization tends to occur and stable glass cannot be obtained.

La ₂ O ₃ is not an essential component, but has an effect of improving the chemical weather resistance of the glass, and its content is up to 5%, preferably up to 2%. If the content of TiO ₂ exceeds 5%, crystallization tends to occur and stable glass cannot be obtained.

Y ₂ O ₃ is not an essential component, but has an effect of improving the chemical weather resistance of the glass, and its content is up to 5%, preferably up to 2%. If the content of TiO ₂ exceeds 5%, crystallization tends to occur and stable glass cannot be obtained.

Fe ₂ O ₃ is not an essential component, but has an effect of suppressing reactivity with the magnetic material, and its content is up to 5%, preferably up to 2%. If the content of Fe ₂ O ₃ exceeds 5%, crystallization becomes easier during heat treatment and a stable glass cannot be obtained.

  MnO is not an essential component, but has an effect of suppressing reactivity with the magnetic material, and its content is up to 5%, preferably up to 2%. When the content of MnO exceeds 5%, crystallization becomes easy during heat treatment, and a stable glass cannot be obtained.

R ₂ O, that is, one or a plurality of alkali metal oxides selected from Li ₂ O, Na ₂ O, K ₂ O, and Cs ₂ O are not essential components, but have an effect of lowering the glass softening temperature. The total content of R ₂ O can be added up to 5%, preferably up to 3%. When the content of R ₂ O exceeds 5%, the tendency to crystallize during heat treatment is significantly increased, and a stable glass cannot be obtained.

In addition to the above components, MgO, BaO, ZrO ₂ , NiO, Nb ₂ O ₅ , MoO ₃ , WO ₃ , TeO ₂ are used in the range of 0 to 5% in order to adjust the viscosity and thermal expansion coefficient of the glass. , Ag ₂ O, etc. can be added.

If MgO, ZrO ₂ , Nb ₂ O, Ag ₂ O, etc. are contained in excess of 5%, crystallization is likely to occur during heat treatment. If the BaO content exceeds 5%, the water resistance is deteriorated and harmful water-soluble BaO is easily eluted, which is not preferable. If the component to be colored such as NiO, MoO ₃ , WO ₃ or the like exceeds 5%, the glass is strongly colored, which makes it difficult to measure the gap depth using an optical microscope or the like.

Since the glass composition of the present invention is a sealing glass for a magnetic head, if the thermal expansion coefficient of the magnetic material used in the magnetic head does not match, the glass and the magnetic material are heated and bonded to the magnetic material. The distortion changes and the electromagnetic conversion characteristics of the magnetic head deteriorate. In addition, the glass is cracked or peeled off during the heat treatment process, polishing process, cleaning process, and the like. Ferrite-based materials are mainly used for this magnetic material. In this ferrite-based magnetic material, the thermal expansion coefficient changes depending on the Fe ₂ O ₃ content. Most of them are from 90 to 135 × 10 ⁻⁷ / ° C. Therefore, the thermal expansion coefficient of the glass composition of the present invention is preferably 85 to 140 × 10 ⁻⁷ / ° C. in consideration of matching with the magnetic material.

  When the temperature of the magnetic material exceeds 750 ° C., the magnetic properties deteriorate, so it is necessary to perform heat treatment at a low temperature. When the glass composition of the present invention is used for sealing with a magnetic material for a magnetic head, sealing can be performed by heat treatment at 550 to 750 ° C. There is a correlation between the heat treatment temperature and the softening point of the glass, and the softening point of the glass composition of the present invention is preferably 650 ° C. or lower. If it exceeds 650 ° C., sealing cannot be performed by heat treatment at 750 ° C.

  The thermal expansion coefficient of the glass composition of the present invention is close to the thermal expansion coefficient of the magnetic material, is excellent in chemical weather resistance not affected by water, polishing liquid, and cleaning liquid, does not react with the magnetic material, and the glass is stable and heat treated. Glass does not crystallize in the process. Therefore, if this glass composition is formed into a glass rod or square bar having a predetermined shape and size and subjected to heat treatment at 550 ° C. to 750 ° C., it can be used for sealing a magnetic material for a magnetic head. it can.

  The above glass composition for a magnetic head can be used for manufacturing a magnetic head in the form of bulk, powder, fiber, thin film or the like. Other shapes may be used. Furthermore, these glass compositions for magnetic heads can be used as a material composed of the glass composition alone or as a composite material of the glass composition and other materials.

Moreover, these glass compositions for magnetic heads are used as a material having a thermal expansion coefficient exceeding the range of 85 × 10 ^{−7 to} 140 × 10 ⁻⁷ / ° C. when used as a composite material with other materials. Can be used.

  FIG. 1 shows an example of a magnetic head according to a fourth aspect of the present invention. A pair of magnetic core halves 1 and 2 having a winding groove at least on one side are interposed via a magnetic gap portion 3. A magnetic head having a butted and bonded structure, in which a pair of magnetic core halves 1 and 2 are bonded by a sealing glass 4. The sealing glass 4 in FIG. 1 is the glass composition according to any one of Examples 1 to 11 (the glass composition shown in claim 1, claim 2 and claim 3).

  Hereinafter, embodiments of the magnetic head of the present invention will be described, but the present invention is not limited thereto.

First, the sealing glass is molded at 660 ° C. on a Mn—Zn single crystal ferrite magnetic material molded into a predetermined shape, the surface is polished, and then SiO ₂ is sputtered as a magnetic gap material, and the magnetic core halves 1, 2 It was created. Next, the magnetic core halves 1 and 2 are brought into contact with each other, held by a jig, and then sealed at 650 ° C. Further, the outer shape is processed into predetermined dimensions and shapes, and then cut into head chips.

  Next, a magnetic head was produced using the produced head chip 5. After the head chip 5 is mounted on the head base 6 and the lead wire 7 is wound around the head chip 5, both ends of the lead wire 7 are soldered to the wiring board on the head base 6 to complete the head shown in FIG. did.

  Since the magnetic head of the present embodiment as described above is not easily crystallized in the heat treatment process at the time of sealing and uses the glass composition for a magnetic head of the present invention having excellent glass stability, electromagnetic conversion It can be supplied as a magnetic head having excellent characteristics.

  In addition, the materials conventionally used can be basically used for the magnetic material and the magnetic gap material in the above magnetic head. The glass composition for a magnetic head in the present invention can also be used for a magnetic head having a structure other than the above magnetic head.

  The glass composition of the present invention is particularly suitable for use as a glass composition for a magnetic head. However, the present invention is not limited to this, and the glass composition of the present invention can be used as an adhesive material, a sealing material, a coating material, or a paste material having various functions such as ceramics, glass and metal. It can be used in place of glass materials conventionally used in various applications including various parts for equipment. For example, various LCR parts, semiconductor packages, other electronic parts, CRTs, fluorescent display tubes, display devices such as plasma display panels, coating materials, sealing materials, fixing materials such as terminals, sealing materials, adhesive materials can do. Furthermore, it can also be used as a sealing material, a fixing material such as a terminal, a sealing material, and an adhesive material in lighting tube products, enamel products, and ceramic products.

The perspective view which shows the outline of the magnetic head by embodiment of this invention The perspective view which shows the outline of the magnetic head by embodiment of this invention

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Magnetic core half 2 Magnetic core half 3 Magnetic gap 4 Sealing glass 5 Magnetic head chip 6 Head base 7 Conductor

Claims (4)

Bi ₂ O ₃ : 20 to 70%, B ₂ O ₃ : 5 to 25%, SiO ₂ : 1 to 23%, ZnO: 0.5 to 20%, Al ₂ O ₃ : _{0.1~10%, SrO: 0~30%,} CaO: 0~35%, TiO 2: 0~5%, La 2 O 3: 0~5%, Y 2 O 3: 0~5%, Fe _{2 O 3: 0~5%, MnO} : 0~5%, R 2 O: 0~5% (R 2 O: Li 2 O, at least one of Na _{2 O,} selected from K ₂ O, Cs 2 O) A glass composition having the following composition: Bi ₂ O ₃ : 40 to 55%, B ₂ O ₃ : 10 to 20%, SiO ₂ : 1 to 10%, ZnO: 5 to 18%, Al ₂ O ₃ : 0. _{5~5%, SrO: 10~20%,} CaO: 0~10%, TiO 2: 0~2%, La 2 O 3: 0~2%, Y 2 O 3: 0~2%, Fe 2 O _{3: 0~2%, MnO: 0~2} %, R 2 O: composition of: _(Li 2 O, at least one selected from _{Na 2 O, K 2 O,} Cs 2 O R 2 O) 0~3% A glass composition characterized by comprising: The glass composition according to claim 1 or 2, which has a thermal expansion coefficient of 85 to 140 x ^10-7 / ° C. A magnetic head in which a winding groove is provided in at least one of a pair of magnetic core halves, and the pair of magnetic cores are joined with a gap portion, wherein the pair of magnetic core halves are defined in claims 1 to 3. A magnetic head, which is bonded with the glass composition according to any one of the above.

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