# US 5,708,543 A · Magnetic head with glass used to bond together two core halves having a coefficient of thermal expansion less than that of the ferromagnetic oxide used to make the core halves

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- Number: US 5,708,543 A
- Document ID: US5708543A
- Status: Granted
- Kind: A
- Application number: 08/655,673
- Filed: 1996-05-30
- Granted: 1998-01-13
- Earliest claimed: 1995-05-31
- Assignees: Sony Corporation
- Inventors: Junichi Honda; Norikatsu Fujisawa
- Web page: https://patentgrep.com/patent/US5708543A

## CPC

- G11B 5/232: {Manufacture of gap}
- Y10T 29/49057: Using glass bonding material
- G11B: INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER (recording measured values in a way that does not require playback through a transducer G01D9/00; recording or playback apparatus using mechanically marked tape, e.g. punched paper tape, or using unit records, e.g. punched or magnetically marked cards G06K; transferring data from one type of record carrier to another G06K1/18; circuits for coupling output of reproducer to radio receiver H04B1/20; gramophone pick-ups or like acoustic electromechanical transducers or circuits therefor H04R)
- Y10T: TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION

## Abstract

A magnetic head according to the present invention can generate excellent readout output even with a reduced track width by controlling the stress applied to the half magnetic cores from the glass. The magnetic head comprises a pair of magnetic cores made of ferromagnetic oxide, at least one of which has a groove for a coil and which are bonded together with the glass with a gap material in-between, wherein the coefficient of thermal expansion of the glass to bond magnetic cores together is smaller than that of the ferromagnetic oxide by 20.times.10.sup.-7 to 35.times.10.sup.-7 per degree Celsius.

## Claims

### Claim 1

A magnetic head, comprising:
a pair of C-shaped magnetic core halves made of a ferromagnetic oxide, at least one of which has a groove for receiving a coil;
a gap filler material which fills a magnetic gap which exists when the core halves are bonded together;
track width controlling grooves formed on opposite sides of the magnetic gap; and
glass bonding the core halves together, the glass filling the track width controlling grooves to bond the core halves together;
a coefficient of thermal expansion of the glass, as measured between 100 and 350 degrees Celsius, is 20.times.10.sup.-7 to 35.times.10.sup.-7 per degree Celsius less than that of the ferromagnetic oxide;
the gap has a length of 0.35 .mu.m or less,
the head has a track width of 25 .mu.m or less,
the bonding of the core halves is conducted with the viscosity of the glass between 4.4 and 4.7 Pa*s, and
the pressure applied to the gap between the core halves in the bonding process is 50 kg*f/cm.sup.2 or less.

### Claim 2 (depends on 1)

The magnetic head of claim 1, wherein the ferromagnetic oxide is selected from the group consisting of Mn--Zn ferrite and Ni--Zn ferrite.

### Claim 3 (depends on 1)

The magnetic head of claim 1, wherein each core half has a layer of gap material within the gap of 900 .ANG. , and the track width is 15 .mu.m and the gap has a depth of 17 .mu.m.

### Claim 4 (depends on 1)

The magnetic head of claim 1, wherein the gap has an azimuth angle.

### Claim 5 (depends on 1)

The magnetic head of claim 1, wherein each of the track width controlling grooves has a depth, as measured between the gap and a respective outer surface of the head of between 200 and 300 .mu.m.

### Claim 6 (depends on 1)

The magnetic head of claim 1, wherein the head has a recording medium facing surface which is convex in shape.

### Claim 7 (depends on 1)

The magnetic head of claim 1, wherein the gap filler material comprises one or more layers of material selected from the group consisting of Pt, Cr, Ti, Ta.sub.2 O.sub.2, Al.sub.2 O.sub.3, SiO.sub.2 and alloys made of Pt, Cr and Ti.