GB2120000A

GB2120000A - Magnetic recording and reproduction

Info

Publication number: GB2120000A
Application number: GB08311308A
Authority: GB
Inventors: Joichiro Ezaki; Hiroshi Kanai; Yoshimi Kitahara
Original assignee: TDK Corp
Current assignee: TDK Corp
Priority date: 1982-04-28
Filing date: 1983-04-26
Publication date: 1983-11-23
Also published as: GB8311308D0; GB8311309D0; GB2120001A; GB2120000B; GB2120001B

Description

SPECIFICATION Magnetic recording and reproduction The present invention relates to a magnetic recording and reproduction system. More particularly, the present invention relates to a magentic recording system for recording a digital signal on a magnetic recording medium such as a magnetic tape, a magnetic disc and so on. The present invention also relates to a magentic recording medium on which a digital signal has been recorded by the above recording system, and to a reproduction system for reproducing the information recorded on the magnetic recording medium.

Conventionally, magnetically recorded information recorded for instance on a magnetic tape, a magnetic disc, or a magnetic sheet, is read out by a magnetic head which has a magnetic core with a thin gap and a coil wound on said core. A magnetic head operates on the principle that the relative movement of the head to the recording medium generates electromotive force in the coil according to the recorded information.

However, that conventional magnetic head has the disadvantage that the recording density on a recording medium is not high. It is said that a conventional magnetic head needs a recording track wider than 30 um.

To solve the above problem, one of the solutions is an optical head which reads out magnetically recorded information using an optic-magnetic effect or the Faraday effect. In an optical head, a magnetic film which has a soft magnetic nature contacts a recording medium carrying magnetically recorded information, and the vertical component of the magnetically recorded information on the recording medium causes corresponding changes in the soft magnetic film. The information in the soft magnetic film is read out optically using the Faraday effect in which an optical beam is subject to the rotation in its plane of polarisation according to the magnetisation of that soft magnetic film. The information in the soft magnetic film is read out optically using the Faraday effect in which an optical beam is subject to the rotation in its plane of polarisation according to the magnetisation of that soft magentic film. As the Faraday effect is used, an optical polariser and an optical analyser are usually used to detect the optical rotation of a polarised optical beam.

Japanese Laid-Open Patent Specification No 1 00713/79 discloses a system for recording a figure or a letter as it is on a magnetic recording medium, and for its reproduction therefrom with an optical technique. This prior system records the data on the recording medium by moving a small magnetic pole relative to the recording medium in accordance with the shape of the data pattern to be recorded. However, this prior system has the disadvantage that its structure becomes very complicated because of the necessity of the relative movement of the small magentic pole and the recording medium in the data pattern to be recorded.

According to this invention a method of recording bits of digital information on a magnetic recording medium comprises moving a magnetic head relative to the magnetic recording medium, differentially magnetising two regions of the magnetic recording medium for each bit of information, the two regions being aligned in a direction transverse to the direction of relative movement between the head and the magnetic medium.

Such recorded information is preferably reproduced by causing the magnetised state of the two regions of the magnetic recording medium to create a magneto-optic effect, comparing the magneto-optic effect created by the two regions and obtaining a differential output indicative of each bit of digital information.

An advantage of the present invention is that the magnetic recording and reproducing system enables a recorded signal to be reproduced with a high signal to noise ratio (S/N).

Another advantage of the present invention is that digital information is recorded in two dimensions and is that an optical reproduction method can be used whereby the magnetically recorded data extending in two dimensions on the magnetic recorded medium can be reproduced.

The various features and aspects of the present invention will now be described with reference to the accompanying drawings; in which :- Figure 1 is a perspective view of a magnetic head and recording medium illustrating the principle of the present invention; Figure 2 is a side elevation of the magnetic head and recording medium; Figure 3 is a diagram of a multi-head recording system; Figure 4 is a partly sectioned diagrammatic side elevation of an optical read-out device; Figure 5 is a cross section through a head of the read-out device; Figure 6 is a microphotograph showing the magnetisation state of a soft magnetic film included in the read-out head when it is in contact with a recorded magnetic medium; and, Figure 7 is a partly sectioned diagrammatic side elevation of another optical read-out device.

In Fig. 1, the reference numeral 1 is a magnetic recording medium with a magnetic recording film 1 a. That recording medium 1 is, for instance, a magnetic tape or a magnetic disc, and the magnetic medium 1 runs in the direction K. The magnetic recording film 1 a may br formed, for example, by depositing any suitable alloy like Co-Cr alloy. The mag-

netic recording head 2 with the gap G and the winding 3 is arranged close to said magnetic recording film 1 a. The winding 3 is energized with a recording signal which is preferably in a digital form. It should be noted in Fig. 1 that the longitudinal direction of the gap G coincides with the running direction K of the magnetic medium while in a conventional magnetic recording system, a gap of a magnetic head is positioned perpendicular to the running direction of the magnetic medium.

Further, it should be appreciated that the width of the gap G is considerably wide (for instance, d = 4 um) as compared with a conventional magnetic head in which a gap width is for instance 0.3-0. 5 Am. A signal to be recorded in this case is supposed to be in digital form, and the pulse width (u sec) of the digital signal is considerably narrower than the wavelength of the recorded signal on the recording medium 1. That wavelength is defined by the moving speed of the medium 1, and the repetition frequency of the signal. In one embodiment, when a tape runs with the speed of 4.7 cm/sec, the pulse width is less than 47 ; sec, and is preferably less than 1.0 sec, sec, still preferably it is nsec order.

In the above configuration, when a recording signal flows in the coil 3, the magnetic flux circulates through the core, the yoke 2a, the area (A) of the medium 1, the area (B), and the yoke 2b. Thus, a pair of magnetic cells A and B, which may be N and S, or S and N are provided on the medium 1 according to the recording signal. Thus, those cells A and B store one bit of information. Those cells A and B may be N and S, or S and N according to the recording information (1 or 0). It should be noted that the shape of the pattern A and B is the same as the shape of the yokes 2a and 2b. Plurality pairs of cells compose a pattern of recorded data.

It should be appreciated that the magnetic flux generated by the winding 3 does not go through the gap G, but the flux goes through the first yoke, the medium and the second yoke, because that gap G is too wide to shunt the magnetic path.

This embodiment has the advantage that a digital recording/reproducing system for two dimentional pattern can be easily and simply constructed because the two dimentional data is stored in the paired cells A and B, the respective shape of the cells becomes substantially same as that of the yoke of the magnetic head facing to the recording medium. Moreover, as the recording signal whose pulse width is considerably narrower than the wavelength of the recorded signa ! used in this embodiment, data can be copied on the recording medium without any influ- ence by the running speed of the recording medium. In this case, if the number of pulses of the recording signal supplied to the wind- ing of the magnetic head is increased to improve the recording density, the duty ratio is restrained to be low. Thus, high density recording can be effected with a low level of consumed electric power.

Moreover, since an elementary information is recorded on the paired cells A and B in this embodiment, the recorded data can be reproduced with a high S/N ratio by obtaining the differential output from the paired cells.

Although the magnetic head is of a redangular shape in the above embodiment, various shape head may be employed in accordance with the reception system of the reproducing apparatus. Moreover, a plurality of two-pole heads may be used for the present magnetic recording/reproducing system. Incidentally, the signal may be recorded not only by the vertical recording system but also the conven- tional horizontal recording system.

The magnetisation direction of the magnetic medium may be perpendicular to the plane of the medium parallel to the plane of the medium or have components in both of these directions.

Fig. 3 shows another example of the magnetic recording method according to the present invention. In this case, a plurality of monopole magnetic heads 2 are arranged at a predetermined interval in the direction perpendicular to the running direction of the medium 1. In this system, respective windings are connected so that current directions of the windings of the adjacnet ones are opposite from each other. In the above configuration, recording is effected in a similar manner as described before. On the other hand, according to the present invention, magnetic recording may be effected with a single monopole magnetic head by switching the direction of the signal current flowing the winding thereof.

In these examples, a two dimensional pattern can also be recorded on the medium in high quality so that the recorded data is reproduced with high S/N ratio upon reproducing.

Fig. 4 shows the optical reproducing system according to the present invention, in which the same reference numerals show the same members as those in the previous figures. The reference numeral 4 is an optical head which operates on the principle of the opt-magnetic effect.

Fig. 5 shows the cross section of that optical head 4 in detail. In Fig. 5, the symbol 4a is a GdGa garnet substrate which is optically transparent and has the thickness of 0.2-0. 5 mm. The symbol 4b is a soft mag- netic film with magnetically soft nature attached on the surface of that substrate 4a.

The symbol 4c is a reflection film attached on the soft magnetic film 4b for reflecting a laser beam, and the symbol 4d is a protection layer of S, 02 attached on the reflection film 4c. The soft magnetic film 4b is made of the optically transparent and soft magnetic material, like YSmCaFeGe group garnet (for instance

Y1. 92SmO. iFGeo. gsOtz). and said soft magnetic film 4b has its easy magnetization axis perpendicular to the film plane, and said soft magnetic film has the thickness of about 6 Am. The optical head 4 is used so that the film 4d contacts the recording medium 1.

When the optical head 4 touches with the recording medium 1, the magnetic domain in the soft magnetic film 4b is magnetized by the vertical component of the recorded data on the medium 1 in the perpandicular direction to the film plane. When a digital signal, like PCM signal is recorded on the medium, the magnetic pattern in the domain in the soft magnetic film is a copy of the digital signal recorded on the medium 1. That magnetic pattern of the domain is read out optically.

Although the optical head 4 is employed in the above system, in one embodiment according to the present invention, the magnetic pattern of the domain of the magnetic recording medium may be directly read out optically without the optical head.

In Fig. 4, the reference numeral 5 is an optical source for generating an optical beam, and is implemented for instance by a light emitting diode (LED), 6 is a polarizer which polarizes linearly the beam from the optical source 5. The numeral 7 is a beam splitter which offsets the horizontal beam in the figure, but passes directly the vertical beam in the figure. The numerals 10 and 11 are a condenser lens and a focusing lens, respectively. The reference numeral 8 is an optical analyzer, and 9 is a CCD device.

In Fig. 4, an optical beam generated by the source 5 illuminates the optical head 4 through the polarizer 6 which polarizes the beam linearly, the beam splitter 7 which reflects or offsets the beam. It is supposed that the beam has some cross section area, and therefore, some area on the optical head 4 is illuminated simultaneously. The beam thus illuminating the optical head 4 is reflected by the reflection film 4c in the optical head 4, and the reflected beam illuminates the CCD device through the beam splitter 7, the lens 11, and the optical analyzer 8. When the beam illuminates the optical head, the polarization is rotated by the Faraday effect in the right or left direction according to the direction of the magnetization in the domain on the soft magnetic film 4b. Since the beam is polarized by the polarizer 6, the output beam from the analyzer 8 is modulated by the rotation direction by the Faraday effect, that is to say, the intensity of the beam at the output of the analyzer 8 depends upon the recorded data. The intensity of the modulated beam of the output of the analyzer 8 illuminates the CCD device 3 so that the two dimension pattern of the data on the medium is copied on the plane of the CCD device.

The optical beam used in the above system may be generated by a ght : emitting diode (LED), a laser and the like. Among them, it is more preferable to use the LED, becouse its cost is relatively low and the dimension of the beam from the LED is larger so that greater imformations can be read out compared with the laser beam.

When the two dimensional pattern has been recorded on the recording medium by the method explained in Figs. 1 and 2, the pattern was stored in the paired cells A and B.

That is to say, the direction of the magnetization of the cell A is opposite to that of the cell B. Accordingly, upon reproducing by the above-mentioned optical reproducing system, respective portions of the soft magnetic film 4b corresponding to the cells A and B are magnetized oppositely to each other. As a result, for instance the corresponding portion to the cell A is subjected to the rightward rotation of the polarization while the corresponding portion to the cell B is subjected to the leftward rotation of the polarization. Therefore, the corresponding portion of the soft magnetic film 4b to the cell B is optically considered as reversal one of that to the cell A. Thus, a differential output is obtained from the above two corresponding portions by means of the reception system 9 to reproduce desired data with a high S/N ratio.

Fig. 6 is a microphotograph showing states of the magnetizations of the soft magnetic film 4b when using the recording method explained in Figs. 1 and 2. It is clearly seen from this microphotograph that the maze domains of the soft magnetic film 4b are varied in accordance with the shape of the yoke of the magnetic head 2 facing the recording medium.

Fig. 7 shows another example of the optical recording system according to the present invention, in which the same reterence numerals show the same member as those in Fig. 4.

Although a plurality of recorded patterns recorded in certain region of the recording medium 1 are read out simultaneously in the system in Fig. 4, the recorded patterns may be read out bit by bit by focussing the laser beam to be spot-like on the soft magnetic film 4b with an objective lens 12, as shown in Fig. 7.

CLAIMS 1. A method of recording bits of digital information on a magnetic recording medium comprising moving a magnetic head relative to the magnetic recording medium, differentially magnetising two regions of the magnetic recording medium for each bit of information, the two regions being aligned in a direction transverse to the direction of relative movement between the head and the magnetic medium.

Claims

2. A method according to claim 1, in which the magnetic medium is differentially magnetised in a direction perpendicular to its

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surface.

3. A method of reproducing digital information from magnetic recording medium which has been prepared by a method according to claim 1 or 2, in which each bit of digital information is recovered by causing the magnetised state of the t'. ", 0 regions of the magnetic recording medium to create a magneto-optic effect, comparing the magneto-optic effect created by the two regions and obtaining a differential output indicative of each bit of digital information.

4. A method according to any one of the preceding claims, in which the pulse width of a signal applied to the magnetic head is small compared to the interval between successive signals bearing in mind the speed of relative movement between the head and the magnetic medium, and size of the head in the direction of relative movement between the head and the magnetic medium, so that, in use, the two regions corresponding to one bit are separated from the two regions corresponding to the following bit in the direction of relative movement between the magnetic head and the magnetic recording medium.

5. A magnetic recording method for recording a two dimensional pattern on a magnetic recording medium comprising: generating magnetic flux according to a shape of a surface of a magnetic head facing to said magnetic recording medium; and recording magnetically said two dimensional pattern on a region of said magnetic recording medium according to the shape of said surface of said magnetic head.

6. The method according to claim 5, in which said magnetic head is energised with a recording signal whose pulse width being considerably small compared with an interval of recorded information.

7. The method according to claim 5 or claim 6, in which said two dimensional pattern is recorded as an elementary information on two regions adjacent each other of said magnetic recording medium, one of said two regions being magnetised oppositely to the another one.

8. The method according to claim 5,6 or 7, in which said two dimensional pattern is recorded by a two-pole magnetic head.

9. The method according to claims 5,6 or 7, in which said two dimensional pattern is recorded by a single monopole magnetic head.

10. A magnetic recording medium in which a two dimensional pattern is recorded as an elementary information on two regions adjacent each other, one of said two regions being magnetised oppositely to the another one.

11. A reproducing method for reproducing a recorded two dimensional pattern which has been recorded as an elementary information on two regions adjacent each other of a magnetic recording medium, in which said two dimensional pattern is obtained by taking out a differential output of the stored data in said two regions.

12. A method according to claim 11, in which the differential output of the vertical components of the magnetisations in said two regions are taken out.

13. A method according to claim 12, in which the recorded two dimensional pattern is read out by using an optic-magnetic effect of a soft magnetic film.

14. A magnetic recording system for recording a pattern on a magnetic recording medium comprising; a magnetic recording head substantially in the shape of a C-ring with a pair of yokes at the ends of the same, a coil wound around said C-ring, and a gap between said yokes, means to cause relative movement between the magnetic recording head and a magnetic recording medium, said gap facing the recording medium and aligned with the relative direction of movement between the head and the recording medium; each of said yokes being parallel to the recording medium, said gap being wide enough so that magnetic flux generated in said C-ring by current flowing in said coil does not short-circuit said gap, but goes through the first yoke, a first region of the recording medium, a second region of said recording medium, and the second yoke of said head, whereby the pattern recorded on the recording medium extends in both the direction of relative movement between the head and the recording medium and also extends in a direction transverse to the direction of relative movement between the head and the recording medium and the shape of said pattern corresponds to the shape of said yokes which face the recording medium.

15. A system according to claim 14, in which the shape of said yoke is rectangular.

16. A magnetic recording system, a magnetic reproduction system or a recorded magnetic recording medium substantially as described with reference to the accompanying drawings.