GB2092807A

GB2092807A - Magnetic head

Info

Publication number: GB2092807A
Application number: GB8137756A
Authority: GB
Original assignee: Olivetti SpA; Ing C Olivetti and C SpA
Current assignee: Telecom Italia SpA; Olivetti SpA
Priority date: 1980-12-16
Filing date: 1981-12-15
Publication date: 1982-08-18
Also published as: IT1129437B; DE3150397A1; JPS57127910A; IT8068910A0

Abstract

The magnetic head 10 is for recording and/or reading digital or analog data on a recording support 11, by magnetising the magnetisable layer 12 of this support perpendicularly. The head comprises a coil 15 which generates a magnetic flux perpendicular to the magnetisable layer, and a first magnetic pole 20 disposed inside the coil and constituted by a thin layer of material of high magnetic permeability disposed on a non-magnetic support plate 21, and of a form which converges towards the recording support in such a manner as to have a very small pole surface 22 in which the entire magnetic flux generated by the coil is concentrated. A second magnetic pole 25 of annular form is disposed coaxially and externally to the coil 15 and has a pole surface in the form of a circular ring which faces the magnetisable layer of the support and is many orders of magnitude larger than the pole surface 22 of the first magnetic pole. <IMAGE>

Description

SPECIFICATION Magnetic head This invention relates to a magnetic head for recording and/or reading data on a recording support of the type in which the recording utilises so-called perpendicular magnetisation. The head comprises a coil arranged to generate a magnetic flux directed substantially perpendicularly to the magnetisable layer of the support, and a magnetic pole arranged to concentrate the flux generated by said coil.

A head for this type of magnetisation is known in which the magnetic pole which concentrates the flux generated by the coil on to the magnetisable support layer is disposed on the opposite side of the magnetisable layer to the coil, and in which the ferrite block which constitutes a secondary pole of the magnetic circuit is located inside the coil. The main drawback of this head is that it requires a relatively complicated positioning apparatus to enable the two parts of the head located on opposite sides of the recording support to be moved and positioned accurately relative to the recording support, while maintaining a fixed position between the two opposing parts. A further drawback of this head is that it has a magnetic flux which travels mainly through air, so considerably lowering the recording efficiency.In this respect, in addition to passing through the two air gaps between the main pole and recording support and between this support and the secondary pole to link up with the coil the useful recording flux returns to the main pole only by way of a long air path.

A magnetic head for perpendicular recording is also known, of which the components are disposed on only one side of the recording support. In order to prevent magnetic saturation of the main pole, the ferrite block is disposed inside the coil to the side of the main pole. This head does not therefore have a true secondary pole in which the magnetic flux links up after it has influenced the recording support; moreover the flux returns to the ferrite block along an air path which is equivalent to or greater than that of the known head comprising two opposing parts.

The technical problem which the present invention seeks to solve is to provide a magnetic head suitable for perpendicularly recording a recording support, which is compact, simple and reliable, in which the magnetic flux has a very small path through air, and of which the ratio of the signal to noise due to external magnetic field induction is high.

This technical problem is solved, and the drawbacks of known heads are obviated, by the magnetic head according to the invention which is defined in the claims below.

The invention will be described in more detail, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a section through a magnetic head embodying the invention; Figure 2 is a section on the line 2-2 of Figure 1 ; and Figure 3 is a partly sectional perspective view of the magnetic head.

With reference to Figures 1 and 3, a magnetic head 10 embodying the invention is arranged to record digital and analog data on a recording support 11 having a first layer 12 characterised by strong magnetic anisotropy in a direction perpendicular to its surface, at least one layer 13 of low coercive force, and an underlying nonmagnetic layer 14 acting as a base for the other layers 12 and 13.

The magnetic head 10 comprises a coil 15 in the form of cylindrical helix and arranged to create a magnetic flux substantially perpendicular to the surface of the support 11. Inside the coil 15 there is disposed a first magnetic recording and/or reading pole 20 constituted by a thin layer of material having a high magnetic permeability at the operating frequency, zero magnetostriction, and high saturation magnetisation, such as for example Mumetal (Registered Trade Mark) or Supermalloy, which is deposited in any known manner on a plate 21, for example of glass. By way of example, the thickness s (Figure 1) of the layer 20 can lie between 0.1 and 2,us. The magnetic pole 20 (Figures 2 and 3) is shaped in plan in such a manner as to concentrate the flow generated by the coil 1 5 towards a first pole surface 22.The width b of the pole surface 22 is for example 300 Mm, so that the area of the surface 22 is not more than 600 mum2. The angle a (Fig 2) by which the layer 20 converges towards the pole surface 22 is desirably less than 600 in order to allow good flux concentration.

The magnetic head 10 also comprises a secondary or closing pole 25 constituted by a ferrite ring disposed coaxially around the coil 15.

For closing the magnetic circuit, a disc 26, also of ferrite, is fixed to the top of the ring 25, and has a groove 27 in which the upper part of the plate 21 and magnetic pole 20 are inserted.

The ring 25 has an outer diameter of about 10 mm, and has a second pole surface 28 of annular shape which is substantially coplanar with the surface 22 of the pole 20 but set back a little therefrom. The surface 28 has an area of about 40 mm2, and is thus many orders of magnitude greater than the area of the surface 33.

A block of 30 of non-magnetic insulating resin inside the coil holds the coil 15 and the plate 20 with its layer 20 embedded inside the ring 25.

The head 10 heretofore described is arranged to record digital or analog data on the support 11, by perpendicularly magnetising the upper layer 12 thereof. More specifically, on energising the coil 15, a magnetic flux is generated orthogonal to the plane of the support 11, and is concentrated by the first magnetic pole 20 into the pole surface 22. The lines of flux, thus concentrated, pass through the air gap facing the recording pole surface 22, to magnetise the layer 1 2 of the support 11, and link up with the closure pole 25 and coil 15 by way of the second layer 13.

The correct operation of the head 10 is based in particular on two factors, namely the concentration of the lines of flux in the main pole by virtue of its shape and high magnetic permeability, and the ratio between the pole surfaces 22 and 28, whereby the flux at the pole surface 28 is too weak to affect the magnetization of the layer 12.

Moreover, because of the annular shape of the secondary pole 25 and the presence of the upper disc 26, which provide true magnetic screening, the head heretofore described is not excessively influenced by the presence of any external magnetic fields, so that the signal-to-noise ratio is very high.

It is apparent that modifications can be made to the magnetic head heretofore described within the scope of the present invention as claimed. For example, it can be suitably dimensioned for reading data already recorded on a recording support of a type heretofore described.

Claims

1. Magnetic head for recording and/or reading data on a recording support by perpendicularly magnetising the magnetisable layer of said support, comprising a coil arranged to generate a magnetic flux substantially perpendicular to the magnetisable layer, a first magnetic pole arranged to concentrate the flux generated by the coil on to the magnetisable layer, and a second magnetic pole arranged to link up with the flux disposed on the same side of the recording support as the first pole, and in which one of the two poles is external to the coil.

2. Magnetic head for recording and/or reading data on a recording support with at least a first layer of strong magnetic anistropy, in a direction substantially perpendicular to its surface, comprising a coil arranged to generate a magnetic flux substantially perpendicular to the surface of the support, a first magnetic pole arranged to concentrate the flux on to a first pole surface facing the first layer, and a second magnetic pole with a second pole surface which also faces the first layer, and of which the area is many orders of magnitude greater than the area of the first pole surface.

3. Magnetic head for recording and/or reading data on a magnetic support by magnetising the magnetisable layer of the support perpendicularly, comprising a coil arranged to generate a magnetic flux substantially perpendicular to the magnetisable layer, and a first magnetic pole arranged to concentrate the flux generated by the coil on to the magnetisable layer, and a ring of ferromagnetic material which is substantially coaxial and external to the coil and is arranged to screen the coil and the first magnetic pole from external magnetic fields.

4. Magnetic head as claimed in claim 1,2 or 3, wherein the first pole comprises a layer of material of high magnetic permeability deposited on a support plate of non-magnetic material.

5. Magnetic head as claimed in any of the preceding claims, wherein the first pole is of a form which converges towards the recording support.

6. Magnetic head as claimed in claim 1 or 2, wherein the second magnetic pole comprises a ring of ferromagnetic material, inside which the coil and the first magnetic pole are located.

7. Magnetic head as claimed in claim 6, wherein a resin block embeds the first pole and the coil inside the second magnetic pole.

8. Magnetic head as claimed in claim 1, wherein the first pole has a first pole surface, and the second magnetic pole has a second pole surface which is substantially coplanar with the first pole surface.

9. Magnetic head as claimed in claim 2 or 8, wherein the area of the first pole surface is of the order of some ym2, and the area of the second pole surface is of the order of some mm2

10. Magnetic head for recording and/or reading data on a recording support, substantially as described with reference to the accompanying drawings.