CA1177577A - Magnetooptical recording medium and recording-and- reproducing device using the same - Google Patents
Magnetooptical recording medium and recording-and- reproducing device using the sameInfo
- Publication number
- CA1177577A CA1177577A CA000381783A CA381783A CA1177577A CA 1177577 A CA1177577 A CA 1177577A CA 000381783 A CA000381783 A CA 000381783A CA 381783 A CA381783 A CA 381783A CA 1177577 A CA1177577 A CA 1177577A
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- Canada
- Prior art keywords
- thin film
- magneto
- information
- recording
- selected region
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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Classifications
-
- G—PHYSICS
- G11—INFORMATION STORAGE
- G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
- G11B11/00—Recording on or reproducing from the same record carrier wherein for these two operations the methods are covered by different main groups of groups G11B3/00 - G11B7/00 or by different subgroups of group G11B9/00; Record carriers therefor
- G11B11/10—Recording on or reproducing from the same record carrier wherein for these two operations the methods are covered by different main groups of groups G11B3/00 - G11B7/00 or by different subgroups of group G11B9/00; Record carriers therefor using recording by magnetic means or other means for magnetisation or demagnetisation of a record carrier, e.g. light induced spin magnetisation; Demagnetisation by thermal or stress means in the presence or not of an orienting magnetic field
- G11B11/105—Recording on or reproducing from the same record carrier wherein for these two operations the methods are covered by different main groups of groups G11B3/00 - G11B7/00 or by different subgroups of group G11B9/00; Record carriers therefor using recording by magnetic means or other means for magnetisation or demagnetisation of a record carrier, e.g. light induced spin magnetisation; Demagnetisation by thermal or stress means in the presence or not of an orienting magnetic field using a beam of light or a magnetic field for recording by change of magnetisation and a beam of light for reproducing, i.e. magneto-optical, e.g. light-induced thermomagnetic recording, spin magnetisation recording, Kerr or Faraday effect reproducing
- G11B11/10582—Record carriers characterised by the selection of the material or by the structure or form
- G11B11/10586—Record carriers characterised by the selection of the material or by the structure or form characterised by the selection of the material
-
- G—PHYSICS
- G11—INFORMATION STORAGE
- G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
- G11B11/00—Recording on or reproducing from the same record carrier wherein for these two operations the methods are covered by different main groups of groups G11B3/00 - G11B7/00 or by different subgroups of group G11B9/00; Record carriers therefor
- G11B11/10—Recording on or reproducing from the same record carrier wherein for these two operations the methods are covered by different main groups of groups G11B3/00 - G11B7/00 or by different subgroups of group G11B9/00; Record carriers therefor using recording by magnetic means or other means for magnetisation or demagnetisation of a record carrier, e.g. light induced spin magnetisation; Demagnetisation by thermal or stress means in the presence or not of an orienting magnetic field
- G11B11/105—Recording on or reproducing from the same record carrier wherein for these two operations the methods are covered by different main groups of groups G11B3/00 - G11B7/00 or by different subgroups of group G11B9/00; Record carriers therefor using recording by magnetic means or other means for magnetisation or demagnetisation of a record carrier, e.g. light induced spin magnetisation; Demagnetisation by thermal or stress means in the presence or not of an orienting magnetic field using a beam of light or a magnetic field for recording by change of magnetisation and a beam of light for reproducing, i.e. magneto-optical, e.g. light-induced thermomagnetic recording, spin magnetisation recording, Kerr or Faraday effect reproducing
- G11B11/10502—Recording on or reproducing from the same record carrier wherein for these two operations the methods are covered by different main groups of groups G11B3/00 - G11B7/00 or by different subgroups of group G11B9/00; Record carriers therefor using recording by magnetic means or other means for magnetisation or demagnetisation of a record carrier, e.g. light induced spin magnetisation; Demagnetisation by thermal or stress means in the presence or not of an orienting magnetic field using a beam of light or a magnetic field for recording by change of magnetisation and a beam of light for reproducing, i.e. magneto-optical, e.g. light-induced thermomagnetic recording, spin magnetisation recording, Kerr or Faraday effect reproducing characterised by the transducing operation to be executed
- G11B11/10504—Recording
-
- G—PHYSICS
- G11—INFORMATION STORAGE
- G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
- G11B11/00—Recording on or reproducing from the same record carrier wherein for these two operations the methods are covered by different main groups of groups G11B3/00 - G11B7/00 or by different subgroups of group G11B9/00; Record carriers therefor
- G11B11/10—Recording on or reproducing from the same record carrier wherein for these two operations the methods are covered by different main groups of groups G11B3/00 - G11B7/00 or by different subgroups of group G11B9/00; Record carriers therefor using recording by magnetic means or other means for magnetisation or demagnetisation of a record carrier, e.g. light induced spin magnetisation; Demagnetisation by thermal or stress means in the presence or not of an orienting magnetic field
- G11B11/105—Recording on or reproducing from the same record carrier wherein for these two operations the methods are covered by different main groups of groups G11B3/00 - G11B7/00 or by different subgroups of group G11B9/00; Record carriers therefor using recording by magnetic means or other means for magnetisation or demagnetisation of a record carrier, e.g. light induced spin magnetisation; Demagnetisation by thermal or stress means in the presence or not of an orienting magnetic field using a beam of light or a magnetic field for recording by change of magnetisation and a beam of light for reproducing, i.e. magneto-optical, e.g. light-induced thermomagnetic recording, spin magnetisation recording, Kerr or Faraday effect reproducing
- G11B11/10502—Recording on or reproducing from the same record carrier wherein for these two operations the methods are covered by different main groups of groups G11B3/00 - G11B7/00 or by different subgroups of group G11B9/00; Record carriers therefor using recording by magnetic means or other means for magnetisation or demagnetisation of a record carrier, e.g. light induced spin magnetisation; Demagnetisation by thermal or stress means in the presence or not of an orienting magnetic field using a beam of light or a magnetic field for recording by change of magnetisation and a beam of light for reproducing, i.e. magneto-optical, e.g. light-induced thermomagnetic recording, spin magnetisation recording, Kerr or Faraday effect reproducing characterised by the transducing operation to be executed
- G11B11/10517—Overwriting or erasing
-
- G—PHYSICS
- G11—INFORMATION STORAGE
- G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
- G11B11/00—Recording on or reproducing from the same record carrier wherein for these two operations the methods are covered by different main groups of groups G11B3/00 - G11B7/00 or by different subgroups of group G11B9/00; Record carriers therefor
- G11B11/10—Recording on or reproducing from the same record carrier wherein for these two operations the methods are covered by different main groups of groups G11B3/00 - G11B7/00 or by different subgroups of group G11B9/00; Record carriers therefor using recording by magnetic means or other means for magnetisation or demagnetisation of a record carrier, e.g. light induced spin magnetisation; Demagnetisation by thermal or stress means in the presence or not of an orienting magnetic field
- G11B11/105—Recording on or reproducing from the same record carrier wherein for these two operations the methods are covered by different main groups of groups G11B3/00 - G11B7/00 or by different subgroups of group G11B9/00; Record carriers therefor using recording by magnetic means or other means for magnetisation or demagnetisation of a record carrier, e.g. light induced spin magnetisation; Demagnetisation by thermal or stress means in the presence or not of an orienting magnetic field using a beam of light or a magnetic field for recording by change of magnetisation and a beam of light for reproducing, i.e. magneto-optical, e.g. light-induced thermomagnetic recording, spin magnetisation recording, Kerr or Faraday effect reproducing
- G11B11/10532—Heads
- G11B11/10534—Heads for recording by magnetising, demagnetising or transfer of magnetisation, by radiation, e.g. for thermomagnetic recording
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N5/00—Details of television systems
- H04N5/76—Television signal recording
- H04N5/78—Television signal recording using magnetic recording
- H04N5/782—Television signal recording using magnetic recording on tape
- H04N5/7824—Television signal recording using magnetic recording on tape with rotating magnetic heads
- H04N5/7826—Television signal recording using magnetic recording on tape with rotating magnetic heads involving helical scanning of the magnetic tape
- H04N5/78263—Television signal recording using magnetic recording on tape with rotating magnetic heads involving helical scanning of the magnetic tape for recording on tracks inclined relative to the direction of movement of the tape
Landscapes
- Engineering & Computer Science (AREA)
- Multimedia (AREA)
- Signal Processing (AREA)
Abstract
TITLE OF THE INVENTION:
Magnetooptical Recording Medium and Recording-and-Reproducing Device Using the Same ABSTRACT OF THE DISCLOSURE:
A Kerr-magnetooptical-effect type recording-and-reproducing device using a recording disk comprising a substrate and magnetic thin films formed over both the major surfaces of the substrate in such a way that their easy directions are perpendicular to the substrate and both the films are magnetized in the same, for instance, upward direction. An optical converging lens and a permanent magnet, which is movable in parallel with or perdencular to the recording disk and rotatable about its axis, are disposed on the opposite sides, respectively t of the recording disk in opposing relationship. A bit is written into or erased from the upper thin film by setting the permanent magnet in such a way that the upwardly or downwardly pointed field is applied to a desired bit yield simultaneous with the focusing of 2 laser beam at the field so as to heat it to a temperature above a Curie point. In like manner the writing or erasing of the lower thin film is effected, but the direction of the write or erasing field is reversed;
that is, the downwardly or upwardly pointed field is applied.
Magnetooptical Recording Medium and Recording-and-Reproducing Device Using the Same ABSTRACT OF THE DISCLOSURE:
A Kerr-magnetooptical-effect type recording-and-reproducing device using a recording disk comprising a substrate and magnetic thin films formed over both the major surfaces of the substrate in such a way that their easy directions are perpendicular to the substrate and both the films are magnetized in the same, for instance, upward direction. An optical converging lens and a permanent magnet, which is movable in parallel with or perdencular to the recording disk and rotatable about its axis, are disposed on the opposite sides, respectively t of the recording disk in opposing relationship. A bit is written into or erased from the upper thin film by setting the permanent magnet in such a way that the upwardly or downwardly pointed field is applied to a desired bit yield simultaneous with the focusing of 2 laser beam at the field so as to heat it to a temperature above a Curie point. In like manner the writing or erasing of the lower thin film is effected, but the direction of the write or erasing field is reversed;
that is, the downwardly or upwardly pointed field is applied.
Description
BACKGROUND OF THE INYENTION-The present invention relates to a magneto-optically erasable recording medium capable of a higher d~gree of recording density and a recording-and-reproducing device using the sameO
So far thermoplastic Pilms, amorphous films or magnetooptical films have been used as optical recording media which can reverse their states and record information with a high density. These o~tical recording media have some defects. For instance, prior to recording, a thermoplastic ~ilm must be subjected to pre-treatment with a corona discharge. In addition, the number of erasure operations is limited because the recorded information must be erased by heating and softening the thermoplastic film. In the case of amorphous films, the thermal transformation between the amorphous ~tate and the crystal state or between the amorphous states is utilized for recording information and the recorded in~ormation is reprod~ced by the opti al detection of the difference in reflectivity or transmissivity resulting from the ~rans-~orn~ation of the film. ~owever, the amorphous film is th~rmodynamically unstable and, thereforet not reliable in operation. In addition, repetitive erasure chaxac-teristics are not uniform. In the case of the magneto optical thin film, information is recorded by switching of the direction of the magnetization, so that the sati~factory erasure of the recorded infor~ation is obtained.
With th~ magnetooptical thin film 9 the Kerr
So far thermoplastic Pilms, amorphous films or magnetooptical films have been used as optical recording media which can reverse their states and record information with a high density. These o~tical recording media have some defects. For instance, prior to recording, a thermoplastic ~ilm must be subjected to pre-treatment with a corona discharge. In addition, the number of erasure operations is limited because the recorded information must be erased by heating and softening the thermoplastic film. In the case of amorphous films, the thermal transformation between the amorphous ~tate and the crystal state or between the amorphous states is utilized for recording information and the recorded in~ormation is reprod~ced by the opti al detection of the difference in reflectivity or transmissivity resulting from the ~rans-~orn~ation of the film. ~owever, the amorphous film is th~rmodynamically unstable and, thereforet not reliable in operation. In addition, repetitive erasure chaxac-teristics are not uniform. In the case of the magneto optical thin film, information is recorded by switching of the direction of the magnetization, so that the sati~factory erasure of the recorded infor~ation is obtained.
With th~ magnetooptical thin film 9 the Kerr
- 2 ;-~, ~'?1.
1 17757~
ma~netooptical effect or the F rady effect is used inreading the information recorded on the film. According to the Kerr magnetooptical technique, the reflected light ls used in reading out the information, so that both major surfaces of a recording ~edium c~n be used. In addition, optical non~niformity of 2 substrate can be tolerated; that is, nonuniformity in optical properties in a substrate will not adversely affect the write, read or erase operation. In this case, the angle of rotation of the plane of polarization of plane-polarized light reflected from a magnetooptical thin f ilm is the most important factor affecting the S/N ratio of the reproduced signal. Therefore, in order to maximize the angle of rotation, a magnetic thin film is formed over the surface of a substrate in such a way that its easy axis direction is perpendicular to the ~urface of the substrate. The magnetic thin film whose easy-axis direction is perpen-dicular to the surface of a substrate will be referred to as "the vertical magnetic thin film" in this specification.
Inf~rmation recorded in the magnetic thin film is read out by irradiating a light beam at ri~ht angles to the film;
~hat ls, by the po~ar Kerr techniqu~. For writing or erasing in~ormation, various technig--es axe used. For instance, as with the conventional magnetic recording, a hea~ i~ used ~or applying a magnetic field strength in excess ~f a coercive force. ~ccording to another technique, a laser beam is focused at a small location or region, so ~hat the temperature of this l~cation or region is heated ~ ~775 ~7 above a Curie point or a magnetic conception temperature and consequently this location or region is demagnetized.
~hen the heated location or region is being cooled, an ex~ernal field or an opposing field from the adjacent locations or regions is applied, so that the location or region is magnetized in a desir~d direction, This technique is advantageous in that the laser beam can be focused at an extremely small spot on the film so that the information recorded at any extremely small location or region can be arbitrarily erased. That is, desired information can be easily added or rewritten. In order to attain the complete erasure of the recorded information, an erasing field must be in excess of a critical or threshold value. In addition, in order to record or erase information only at a desired spot without magnetically disturbing the adjacent regions, a write or erasing field to be applied must be lower than a coercive force, The critical or threshold erasing field strength is dependent upon types, compositions and thickness of magnetooptical films and the diameter Q~ bits. It is in general between 100 and 1 000 Oe. In order to erase the recorded information, an erasing field in excess of such critical or threshold erasing field strength must be applied pexpendicular to a magnetic recording medium or disk by means of a magnetic-field-yenerating means disposed out of contact with ~he-recording medium or disk. To this end, there has been invented and demonstrated a system in which an air-core coil is located as close to a recording medium as possible and a writing or detecting light beam 5 ~ ~
is passed throush the coil. In the write operation a current is made to pass the coil in one direction, but in the erase operation, a current is reversed in the other direction. Alternatively~ a current is made to flow only in the erase operation. In practice, however, a magneto-motive force in exc~ss of 100 AT is needed. That is, an exciting current in excess of a few amperes must flow through a coil with more than one hundred turns. As a result, coils and power supplies large in size are needed, so that magnetic-field application systems become largP
in size. There has been also proposed a technique for passing a pulsating currer.t through a coil, thereby generating a pulsating field. However, this technique is impractical because its time response is toc slow to erase the recorded information at a rate in eXcesC o~ 1 M bit/sec.
In order to obtain a high magnetic field strength with a low magnetomotive force, there has been proposed a technique for polishing the point of a magnetic needle with a diameter of bout 200 ~m and winding a coil around the needle. However, the field strength abruptly drops with the distance away frcm the point of the needle, so that it is almost next to impossible to use the magnetic needle without contact with a recording medium. In a~dition, a control system is needed capable of locating the point of the magr.etic needle at a spot at which the recorded information is to be erased with an extremely high degree of accuracy.
_ 5 _ ~ ~7577 SUMMARY OF THE INVENTION
.
The present invention provides a Kerr-magneto-optical-effect type recording-and-reproducing device of the type detecting and reproducing the light beam reflected from a magnetooptical reccrding medium~ A movable and rotatable permanent magnet is disposed at one side of the recordins medium while an optical convergins lens is disposed at the other side thereof. Information is recorded or erased by moving and/or rotating the permanent magnet so that the direction of the magnetic field applied from the permanent magnet to the recording meaium is changed and simultaneously irradiating a light beam to 2 desired spot on the recording medium so as to heat the same~
The present invention uses a magnetooptical recording medium of the type comprising a substrate and vertical magnetic thin films which are formed over the major surfaces of the substrate in such a way that their easy-axis directions are perpendicular to the major surfaces of the - substrate, ~he thin films being previously magnetized in the same direction.
In the write or erase operation of one magnetic thin film, a write or erasinq field in one direction is applied, but in the write or erase operation of the o~her magnetic thin film, the field is reversed to the opposite direction.
As compared with the prior art magnetooptical recording medium and the recording~and~reproducing device using the same, the present invention has the following 1 ~7~77 novel effects, features and advantages:
(1) In the prior art device, an exciting current is made to flow ~u~ugh a coil in the write or erase operation, but according to the present invention this arrangement can be eliminated. That is, a power supply for flowing a current through the coil can be eliminated. As a result, the recording-and-reproducing device in accordance with the present invention can be made compac~ in size and light in weight. In addition, the degradation in reliability in operation resulting from the heat dissipation from the coil can be a~cided.
(2) A permanent magnet which is small in size is disposed at one side of a magnetooptical recording medium and outside of the path of the write, erase or read light beam. As a result, an optical system can be designed and constructed more freely.
1 17757~
ma~netooptical effect or the F rady effect is used inreading the information recorded on the film. According to the Kerr magnetooptical technique, the reflected light ls used in reading out the information, so that both major surfaces of a recording ~edium c~n be used. In addition, optical non~niformity of 2 substrate can be tolerated; that is, nonuniformity in optical properties in a substrate will not adversely affect the write, read or erase operation. In this case, the angle of rotation of the plane of polarization of plane-polarized light reflected from a magnetooptical thin f ilm is the most important factor affecting the S/N ratio of the reproduced signal. Therefore, in order to maximize the angle of rotation, a magnetic thin film is formed over the surface of a substrate in such a way that its easy axis direction is perpendicular to the ~urface of the substrate. The magnetic thin film whose easy-axis direction is perpen-dicular to the surface of a substrate will be referred to as "the vertical magnetic thin film" in this specification.
Inf~rmation recorded in the magnetic thin film is read out by irradiating a light beam at ri~ht angles to the film;
~hat ls, by the po~ar Kerr techniqu~. For writing or erasing in~ormation, various technig--es axe used. For instance, as with the conventional magnetic recording, a hea~ i~ used ~or applying a magnetic field strength in excess ~f a coercive force. ~ccording to another technique, a laser beam is focused at a small location or region, so ~hat the temperature of this l~cation or region is heated ~ ~775 ~7 above a Curie point or a magnetic conception temperature and consequently this location or region is demagnetized.
~hen the heated location or region is being cooled, an ex~ernal field or an opposing field from the adjacent locations or regions is applied, so that the location or region is magnetized in a desir~d direction, This technique is advantageous in that the laser beam can be focused at an extremely small spot on the film so that the information recorded at any extremely small location or region can be arbitrarily erased. That is, desired information can be easily added or rewritten. In order to attain the complete erasure of the recorded information, an erasing field must be in excess of a critical or threshold value. In addition, in order to record or erase information only at a desired spot without magnetically disturbing the adjacent regions, a write or erasing field to be applied must be lower than a coercive force, The critical or threshold erasing field strength is dependent upon types, compositions and thickness of magnetooptical films and the diameter Q~ bits. It is in general between 100 and 1 000 Oe. In order to erase the recorded information, an erasing field in excess of such critical or threshold erasing field strength must be applied pexpendicular to a magnetic recording medium or disk by means of a magnetic-field-yenerating means disposed out of contact with ~he-recording medium or disk. To this end, there has been invented and demonstrated a system in which an air-core coil is located as close to a recording medium as possible and a writing or detecting light beam 5 ~ ~
is passed throush the coil. In the write operation a current is made to pass the coil in one direction, but in the erase operation, a current is reversed in the other direction. Alternatively~ a current is made to flow only in the erase operation. In practice, however, a magneto-motive force in exc~ss of 100 AT is needed. That is, an exciting current in excess of a few amperes must flow through a coil with more than one hundred turns. As a result, coils and power supplies large in size are needed, so that magnetic-field application systems become largP
in size. There has been also proposed a technique for passing a pulsating currer.t through a coil, thereby generating a pulsating field. However, this technique is impractical because its time response is toc slow to erase the recorded information at a rate in eXcesC o~ 1 M bit/sec.
In order to obtain a high magnetic field strength with a low magnetomotive force, there has been proposed a technique for polishing the point of a magnetic needle with a diameter of bout 200 ~m and winding a coil around the needle. However, the field strength abruptly drops with the distance away frcm the point of the needle, so that it is almost next to impossible to use the magnetic needle without contact with a recording medium. In a~dition, a control system is needed capable of locating the point of the magr.etic needle at a spot at which the recorded information is to be erased with an extremely high degree of accuracy.
_ 5 _ ~ ~7577 SUMMARY OF THE INVENTION
.
The present invention provides a Kerr-magneto-optical-effect type recording-and-reproducing device of the type detecting and reproducing the light beam reflected from a magnetooptical reccrding medium~ A movable and rotatable permanent magnet is disposed at one side of the recordins medium while an optical convergins lens is disposed at the other side thereof. Information is recorded or erased by moving and/or rotating the permanent magnet so that the direction of the magnetic field applied from the permanent magnet to the recording meaium is changed and simultaneously irradiating a light beam to 2 desired spot on the recording medium so as to heat the same~
The present invention uses a magnetooptical recording medium of the type comprising a substrate and vertical magnetic thin films which are formed over the major surfaces of the substrate in such a way that their easy-axis directions are perpendicular to the major surfaces of the - substrate, ~he thin films being previously magnetized in the same direction.
In the write or erase operation of one magnetic thin film, a write or erasinq field in one direction is applied, but in the write or erase operation of the o~her magnetic thin film, the field is reversed to the opposite direction.
As compared with the prior art magnetooptical recording medium and the recording~and~reproducing device using the same, the present invention has the following 1 ~7~77 novel effects, features and advantages:
(1) In the prior art device, an exciting current is made to flow ~u~ugh a coil in the write or erase operation, but according to the present invention this arrangement can be eliminated. That is, a power supply for flowing a current through the coil can be eliminated. As a result, the recording-and-reproducing device in accordance with the present invention can be made compac~ in size and light in weight. In addition, the degradation in reliability in operation resulting from the heat dissipation from the coil can be a~cided.
(2) A permanent magnet which is small in size is disposed at one side of a magnetooptical recording medium and outside of the path of the write, erase or read light beam. As a result, an optical system can be designed and constructed more freely.
(3) A focal-point control coil and a permanent magnet are spaced apart from each other by a suitable distance so that the magnetic interference of the permanent 2D magnet on the ccntrol coil can be avoided. Such magnetic interference would adversely affect the precise movement of the control coil.
(4) The permanent magnet has a strong strength even though it is small in size so that it can be spaced apart from a magnetooptical recording medium by a suitable distance.
~ 5) The permanent magnet is extended to some extent in parallel with the recording medium. As a result, 1 17757~
the field strength w~ll not abruptly change in the directions in parallel with the surface of the recording medium so that the precise alignment or registration between the permanen~ magnet and a spot on the recording medium at which the recordea information is erased is not needed.
(6) The present invention uses a magnetooptical recording medium or disk of the type comprising a substrate and magnetic thin film~ formed over both the major surfaces thereof. As a consequence, a field distribution can be established in such a way that the field distribution over one magnetic thin film is higher than a critical or threshold erasing field strength while the field distri-bution over the other magnetic thin film is less than a coercive force of the film. As a result, recording disks with higher packing or recording densities can be provided.
(7~ In the write or erase operation of one magnetic thin film, a write or erasing field in one di-rection is applied, but in the case of the write or erase operatlon of the other magnetic thin film, the permanent magnet is rotated through 180, so that the direction of the write or erasing field is reversed. Th~refore, both the magnetic thin films can be previously m~gn~tized in the same direction and consequently th~ fabrication of recording disks can be much facilitated.
Mbre particularly, there is provided:
A ~agneto-op~i~ recording and reproducins device ~or ~oring infor~a~ion on a~d r~producing in~or~a~ion from a ffligneto opti~ record medium, said record medium having a ~ubstrate and upper and lower ~agneto-optic thin films formed on opposed major surface~ o~ said substrate, each of said fil~s having an axis of easy magneti~ation perpendicular to said ma]or surfaces, said recording and reproducîng device comprising:
an op~ical head including a converging optical lens for focu~ing a light bea~ on a selected region of a selected 7757~
one of said upper ~nd lower ~agneto-opti~ thin ~ilms, said optical head having ~i) a recording mode in which said focu~ed ~ight beam alters the structure of said selected region of said upper magneto-optic thin film to enable an externally applied magnetic field to record information on said selected region of said ~pper magnet~-optic thin film, ($i) an erase mode in which said focu~ed light beam alters the structure of said selected region of said upper ~agneto-optic thin film to enable an externally applied magnetic field to erase any information stored therein, and (iii) a reproduce mode in whic~ said optical ~ead optically detects t~e lig~t of said focused light beam reflected from said sele~ted region of a selected one of said upper and lower ma~neto-optic thin films to generate a signal corresponding to information recorded therein;
a permanent magnet disposed in alignment with said focused light beam so that ~aid record medium may be disposed bet~een said optical head and said permanent magnet, wit~
~aid ~pper ~ag~eto-optic thin ~ilm adjacent said optical head and said lower magneto-optic thin film ad jacent said per-manent magnet;
means operative in said recording mode to cause the intensity of ~aid focused light beam ~o be sufficient to (i~
hea~ on~y ~aid selected region of said upper magneto-opti~
e~in film to a te~per3ture sufficiently high ~o enable said permanent magnet to record in~ormation on said sele~ted region, and to simultaneously (ii) ~ove said permanent magnet with respect to said selected region so as to magneticaily record information ~n said selected region; and means opera~ive in said erase mode to cause the ~ntensity of said focused liqht beam to be suffi~ient to ~i) heat only 6aid selected regi~n of said upper magneto-op~ic thin film eo ~ temperature sufficiently ~igh to enable ~aid permanent magnet to erase information on said selected region by subjeoting eaid upper ~agneto optic ~hin film to 1 17~5'~
magnetic field having a field strength abvve a critical or threshold erasing field strength ~nd to simultaneously ~ii) move ~aid permanent magnet ~ith respect to said selected region so as to magne~ically er~se information from said selected reg ion, said eritical or threshold erasing field strength being less than the coercive orce of said lower magneto--opti~ thin film, so that said- permanent magnet may erase infozmation from said selected region of said upper magneto--optic t~in film withou~ disturbing information stored in the adjacent portion of said lower magne~o-optic thin film.
BRIEF DESCRIPTION OF THE DRAWINGS:
Fig. 1 is a view ~sed for the explanation of the underlying principle of the present invention;
-8b-~ ~7~5 7'~
Fig. 2 shows a schematic view of a preferred embodiment of a recording-and-reproducing device in accordance with the present invention Fig. 3A shows a permanent magnet used in the present invention;
Fig. 3B shows the relationship betwe~n the distance between the permanent magnet shown in Fig. 3A and a recording medium on the one hand and the field strength on the other hand; and Figs. 4A and 4B show in cross sections of magnetooptical recording media or disks, respectively, in accordance with the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS:
The present invention was made to overcome the above-described problems encountered in recording-and-reproducing devices based on the Kerr magnetooptical effect and provides a recording-and-reproducing device capable of erasing any desired information by utilizing the strong magnetic field of a permanent magnet. The present invention will become apparent from the following description of preferred embodiments thereof taken in conjunction with the accompanying drawings.
Referring first to Fig. 1, the underlying principle of the presen~ invention; that is, the process for erasing the recorded information will be described.
An erasing field HeX and a write field H~. are antiparallel.
A vertical thin magnetic film 1 has the vertical easy-axis ~ ~77~7~
directions. A small spot or domain 1a has its magnetization reversed when the information is written by the thermo-magnetic effect resulting from the coaction of opposing or demagnetizing fields 2 generated from adjacent regions 1b which are magnetized in one direction, the write field 3 and a light beam 4. In the case of erasing, the reversely magnetized domain 1a is heated to a temperature in excess of a Curie point by the light beam 4 and applied with the erasing field 5 against the demagnetizing fields 2. While the domain 1a is being cooled, the direction of magneti-zation is reversed as in the adiacent regions 1b and stabilized. In order to attain a complete erasure, the erasing field HeX must be greater than a critical or threshold value H~l but smaller than a coercive force Hc, so that onl~ a needed domain or regior, is erased while the reversal in the direction of magnetization is avoided in the adjacent or unwanted domain or region.
In Fig. 2 is shown the construction of an embodiment of the present invention. Reference numeral 23 denotes a light source such as a laser; 24, a converging lens; 25, a focal-point control coil which is adapted to displace the converging lens 24, whereby its focal point is shifted; 6, a substrate made of a syntheti~ resin or glass; 7, vertical magnetic thin films; 8, a small permanent magnet; and 9, a motor.
The converging lens 24 and the permanent magnet 8 are disp~sed in opposed relationship with each other with the magnetic thin films 7 interposed therebetween. The ~ ~7'~57~
permanent magnet 8 is displaced both horizontally and vertically as indicated by double-pointed arrows B and A, respectively, and further is rotated in the direction indicated by the arrow C.
Next, the step for erasing the recorded infor-mation will be described~ A lzser beam is focused upon a desired region of the magnetic thin film 7 so that the region to be erzsed is heated to a temperature in excess ` of a Curie point or magnetic conception temperature.
Simultaneously, the permanent ma~net 8 is displaced and/or rotated in such a way that the field in the region to be erased is reversed in direction and is maintained greater than a critical or threshold erasing field Hel but lower than a coercive force Hc of the maynetic thin film 7. Then, when the temperature of the region to be erased drops, the direction of magnetization is reversed and stabilized, whereby the recorded information is erased.
Next, some experimental results will be described.
Mn~ Cu and Bi are deposited by the conventional vacuum deposition technique over both the major surfaces of the substrate so as to form magnetic thin films approximately 500 A in thickness. Th~s a magnetooptical disk is provided which has a coercive force of 2000 Oe. With the thermo-magnetic recording technique utilizing a laser beam, information signals with a bït width or spacing of about one ~m are recorded on the disk~
Fig. 3B shows the relationship between the magnetic field strength in Oe and the distance measured ~ ~7'7~7 immediately above a permanent magnet which is made o~ SmCo5 and 1 cm x 1 cm x 3 c~. in size as shown in Fig. 3A.
With t~e disk of the type described, the permanent magnet as shown in Fig. 3A and the arrangement as shown in Fig. 2, the tests ~iere conducted by varying the distance between the permanent magnet and the disk. It was found out that the critical or threshold erasing field Hel is about 300 Oe and that the complete erasure can be assured when an erasing field higher than 300 Oe is applied. It was also found out that when an erasing field less than 130 Oe is applied, the write operation results. With an erasing field of a magnitude intermediate between 130 Oe and 300 Oe, incomplete erasure results.
In Fig. 3B, the experimental data from 10 to 20 are shown. When the permanent magnet is spaced a~art from the magnetic thin film or disk by a distance longer than 1.5 mm, the field strength is less than 1 500 Oe, so that the reversal of the magnetization will not occur and consequently the ~nfor~ation on the p~rtion which is unnecess;lry to erase the information thereon is not erased. rne critical or threshold eraslng field of about 300 Oe is obtained only when the distance between the permanent magnet and the magnetic thin ~ilm or disk is less than 9.5 mm. Therefore, with a disk having the magnetic thin films formed over both the major surfaces thereof, the complete erasure is ensured when the distance between the permanent magnet and the disk is maintained between 1O5 and 9.S mm. Thus, with the magnetic thin fiim disk of the thickness between 1.5 and 9.5 mm, the magnetooptic ~ :~775'~
recording-and~reproducing device can be designed and constructed with much tolerances. Any information recorded at any locations or regions can be arbitrarily erased so that new information can be recorded again.
The disk which has magnetic thin films over both the major surfaces thereof and whi.ch is used in the present i.nvention and the device for erasing the information recorded on the disk will be described below in more detail.
The write and erase operationc by using both a light beam and an erasing field have been already described~ In order to record information, a vertical magnetic thin film must be previously magnetized in one direction. To this end, the vertical magnetic thin film is interposed between the N- and S-poles and a magnetic field is applied to the magnetic thin film to such an extent that the magnetization of the magnetic thin film is sufficiently saturated. In the case of the reflection type recording disk hav.ing the magnetic thin films formed over both the major surfaces thereof, the direction of the magnetization of both the upper and lower magnetic thin f ilms 7 and 7a is same; th~t is, upward as shown in Fig. 4A. It follows, therefore, that the directions of the magnetization are opposite when viewed from the above and below. If it is desired that the directions of the magnetization are symmetrical about the substrate as shown in Fig. 4B, two disks comprising substrates 6 and 6a and magnetic thin films 7 and 7a~
respectively, are magnetized i.ndependently o each other and then the substrates 6 and 6a are bcnded together so ;~ ~ V~ i7 ~s~ ~
as to provide a disk.
According to the present invention, reflection type disks can be fabricated in a simple manner and magnetiæed in one step. In addition, the recorded informatior. can be completely erased by a simple device as will be described below.
In the case of the write or erase operation of one magnetic thin film 7 of the disk as shown in Fig. 4A, the write or erasing field in one directior. is zpplied, but in the case of the write or erase operation of the other magnetic thin film 7a' the write or erasing field is reversed in direction. That is, when an information is recorded or erased on the lower magnetic thin film 7a' the permanent magnet 8 is rotated through 180 as indicated by th~ arrow C in Fig. 2.
In summary, according to the present invention the magnetic thin films of the reflection type recording disk can be simultaneously magnetized and with the simple device the write and erase operations can be carried out.
As a result, the packing or recording density can be increasedO In addition, the fabrication of recording disks can be much facilitatedO
~ 5) The permanent magnet is extended to some extent in parallel with the recording medium. As a result, 1 17757~
the field strength w~ll not abruptly change in the directions in parallel with the surface of the recording medium so that the precise alignment or registration between the permanen~ magnet and a spot on the recording medium at which the recordea information is erased is not needed.
(6) The present invention uses a magnetooptical recording medium or disk of the type comprising a substrate and magnetic thin film~ formed over both the major surfaces thereof. As a consequence, a field distribution can be established in such a way that the field distribution over one magnetic thin film is higher than a critical or threshold erasing field strength while the field distri-bution over the other magnetic thin film is less than a coercive force of the film. As a result, recording disks with higher packing or recording densities can be provided.
(7~ In the write or erase operation of one magnetic thin film, a write or erasing field in one di-rection is applied, but in the case of the write or erase operatlon of the other magnetic thin film, the permanent magnet is rotated through 180, so that the direction of the write or erasing field is reversed. Th~refore, both the magnetic thin films can be previously m~gn~tized in the same direction and consequently th~ fabrication of recording disks can be much facilitated.
Mbre particularly, there is provided:
A ~agneto-op~i~ recording and reproducins device ~or ~oring infor~a~ion on a~d r~producing in~or~a~ion from a ffligneto opti~ record medium, said record medium having a ~ubstrate and upper and lower ~agneto-optic thin films formed on opposed major surface~ o~ said substrate, each of said fil~s having an axis of easy magneti~ation perpendicular to said ma]or surfaces, said recording and reproducîng device comprising:
an op~ical head including a converging optical lens for focu~ing a light bea~ on a selected region of a selected 7757~
one of said upper ~nd lower ~agneto-opti~ thin ~ilms, said optical head having ~i) a recording mode in which said focu~ed ~ight beam alters the structure of said selected region of said upper magneto-optic thin film to enable an externally applied magnetic field to record information on said selected region of said ~pper magnet~-optic thin film, ($i) an erase mode in which said focu~ed light beam alters the structure of said selected region of said upper ~agneto-optic thin film to enable an externally applied magnetic field to erase any information stored therein, and (iii) a reproduce mode in whic~ said optical ~ead optically detects t~e lig~t of said focused light beam reflected from said sele~ted region of a selected one of said upper and lower ma~neto-optic thin films to generate a signal corresponding to information recorded therein;
a permanent magnet disposed in alignment with said focused light beam so that ~aid record medium may be disposed bet~een said optical head and said permanent magnet, wit~
~aid ~pper ~ag~eto-optic thin ~ilm adjacent said optical head and said lower magneto-optic thin film ad jacent said per-manent magnet;
means operative in said recording mode to cause the intensity of ~aid focused light beam ~o be sufficient to (i~
hea~ on~y ~aid selected region of said upper magneto-opti~
e~in film to a te~per3ture sufficiently high ~o enable said permanent magnet to record in~ormation on said sele~ted region, and to simultaneously (ii) ~ove said permanent magnet with respect to said selected region so as to magneticaily record information ~n said selected region; and means opera~ive in said erase mode to cause the ~ntensity of said focused liqht beam to be suffi~ient to ~i) heat only 6aid selected regi~n of said upper magneto-op~ic thin film eo ~ temperature sufficiently ~igh to enable ~aid permanent magnet to erase information on said selected region by subjeoting eaid upper ~agneto optic ~hin film to 1 17~5'~
magnetic field having a field strength abvve a critical or threshold erasing field strength ~nd to simultaneously ~ii) move ~aid permanent magnet ~ith respect to said selected region so as to magne~ically er~se information from said selected reg ion, said eritical or threshold erasing field strength being less than the coercive orce of said lower magneto--opti~ thin film, so that said- permanent magnet may erase infozmation from said selected region of said upper magneto--optic t~in film withou~ disturbing information stored in the adjacent portion of said lower magne~o-optic thin film.
BRIEF DESCRIPTION OF THE DRAWINGS:
Fig. 1 is a view ~sed for the explanation of the underlying principle of the present invention;
-8b-~ ~7~5 7'~
Fig. 2 shows a schematic view of a preferred embodiment of a recording-and-reproducing device in accordance with the present invention Fig. 3A shows a permanent magnet used in the present invention;
Fig. 3B shows the relationship betwe~n the distance between the permanent magnet shown in Fig. 3A and a recording medium on the one hand and the field strength on the other hand; and Figs. 4A and 4B show in cross sections of magnetooptical recording media or disks, respectively, in accordance with the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS:
The present invention was made to overcome the above-described problems encountered in recording-and-reproducing devices based on the Kerr magnetooptical effect and provides a recording-and-reproducing device capable of erasing any desired information by utilizing the strong magnetic field of a permanent magnet. The present invention will become apparent from the following description of preferred embodiments thereof taken in conjunction with the accompanying drawings.
Referring first to Fig. 1, the underlying principle of the presen~ invention; that is, the process for erasing the recorded information will be described.
An erasing field HeX and a write field H~. are antiparallel.
A vertical thin magnetic film 1 has the vertical easy-axis ~ ~77~7~
directions. A small spot or domain 1a has its magnetization reversed when the information is written by the thermo-magnetic effect resulting from the coaction of opposing or demagnetizing fields 2 generated from adjacent regions 1b which are magnetized in one direction, the write field 3 and a light beam 4. In the case of erasing, the reversely magnetized domain 1a is heated to a temperature in excess of a Curie point by the light beam 4 and applied with the erasing field 5 against the demagnetizing fields 2. While the domain 1a is being cooled, the direction of magneti-zation is reversed as in the adiacent regions 1b and stabilized. In order to attain a complete erasure, the erasing field HeX must be greater than a critical or threshold value H~l but smaller than a coercive force Hc, so that onl~ a needed domain or regior, is erased while the reversal in the direction of magnetization is avoided in the adjacent or unwanted domain or region.
In Fig. 2 is shown the construction of an embodiment of the present invention. Reference numeral 23 denotes a light source such as a laser; 24, a converging lens; 25, a focal-point control coil which is adapted to displace the converging lens 24, whereby its focal point is shifted; 6, a substrate made of a syntheti~ resin or glass; 7, vertical magnetic thin films; 8, a small permanent magnet; and 9, a motor.
The converging lens 24 and the permanent magnet 8 are disp~sed in opposed relationship with each other with the magnetic thin films 7 interposed therebetween. The ~ ~7'~57~
permanent magnet 8 is displaced both horizontally and vertically as indicated by double-pointed arrows B and A, respectively, and further is rotated in the direction indicated by the arrow C.
Next, the step for erasing the recorded infor-mation will be described~ A lzser beam is focused upon a desired region of the magnetic thin film 7 so that the region to be erzsed is heated to a temperature in excess ` of a Curie point or magnetic conception temperature.
Simultaneously, the permanent ma~net 8 is displaced and/or rotated in such a way that the field in the region to be erased is reversed in direction and is maintained greater than a critical or threshold erasing field Hel but lower than a coercive force Hc of the maynetic thin film 7. Then, when the temperature of the region to be erased drops, the direction of magnetization is reversed and stabilized, whereby the recorded information is erased.
Next, some experimental results will be described.
Mn~ Cu and Bi are deposited by the conventional vacuum deposition technique over both the major surfaces of the substrate so as to form magnetic thin films approximately 500 A in thickness. Th~s a magnetooptical disk is provided which has a coercive force of 2000 Oe. With the thermo-magnetic recording technique utilizing a laser beam, information signals with a bït width or spacing of about one ~m are recorded on the disk~
Fig. 3B shows the relationship between the magnetic field strength in Oe and the distance measured ~ ~7'7~7 immediately above a permanent magnet which is made o~ SmCo5 and 1 cm x 1 cm x 3 c~. in size as shown in Fig. 3A.
With t~e disk of the type described, the permanent magnet as shown in Fig. 3A and the arrangement as shown in Fig. 2, the tests ~iere conducted by varying the distance between the permanent magnet and the disk. It was found out that the critical or threshold erasing field Hel is about 300 Oe and that the complete erasure can be assured when an erasing field higher than 300 Oe is applied. It was also found out that when an erasing field less than 130 Oe is applied, the write operation results. With an erasing field of a magnitude intermediate between 130 Oe and 300 Oe, incomplete erasure results.
In Fig. 3B, the experimental data from 10 to 20 are shown. When the permanent magnet is spaced a~art from the magnetic thin film or disk by a distance longer than 1.5 mm, the field strength is less than 1 500 Oe, so that the reversal of the magnetization will not occur and consequently the ~nfor~ation on the p~rtion which is unnecess;lry to erase the information thereon is not erased. rne critical or threshold eraslng field of about 300 Oe is obtained only when the distance between the permanent magnet and the magnetic thin ~ilm or disk is less than 9.5 mm. Therefore, with a disk having the magnetic thin films formed over both the major surfaces thereof, the complete erasure is ensured when the distance between the permanent magnet and the disk is maintained between 1O5 and 9.S mm. Thus, with the magnetic thin fiim disk of the thickness between 1.5 and 9.5 mm, the magnetooptic ~ :~775'~
recording-and~reproducing device can be designed and constructed with much tolerances. Any information recorded at any locations or regions can be arbitrarily erased so that new information can be recorded again.
The disk which has magnetic thin films over both the major surfaces thereof and whi.ch is used in the present i.nvention and the device for erasing the information recorded on the disk will be described below in more detail.
The write and erase operationc by using both a light beam and an erasing field have been already described~ In order to record information, a vertical magnetic thin film must be previously magnetized in one direction. To this end, the vertical magnetic thin film is interposed between the N- and S-poles and a magnetic field is applied to the magnetic thin film to such an extent that the magnetization of the magnetic thin film is sufficiently saturated. In the case of the reflection type recording disk hav.ing the magnetic thin films formed over both the major surfaces thereof, the direction of the magnetization of both the upper and lower magnetic thin f ilms 7 and 7a is same; th~t is, upward as shown in Fig. 4A. It follows, therefore, that the directions of the magnetization are opposite when viewed from the above and below. If it is desired that the directions of the magnetization are symmetrical about the substrate as shown in Fig. 4B, two disks comprising substrates 6 and 6a and magnetic thin films 7 and 7a~
respectively, are magnetized i.ndependently o each other and then the substrates 6 and 6a are bcnded together so ;~ ~ V~ i7 ~s~ ~
as to provide a disk.
According to the present invention, reflection type disks can be fabricated in a simple manner and magnetiæed in one step. In addition, the recorded informatior. can be completely erased by a simple device as will be described below.
In the case of the write or erase operation of one magnetic thin film 7 of the disk as shown in Fig. 4A, the write or erasing field in one directior. is zpplied, but in the case of the write or erase operation of the other magnetic thin film 7a' the write or erasing field is reversed in direction. That is, when an information is recorded or erased on the lower magnetic thin film 7a' the permanent magnet 8 is rotated through 180 as indicated by th~ arrow C in Fig. 2.
In summary, according to the present invention the magnetic thin films of the reflection type recording disk can be simultaneously magnetized and with the simple device the write and erase operations can be carried out.
As a result, the packing or recording density can be increasedO In addition, the fabrication of recording disks can be much facilitatedO
Claims (4)
1. A magneto-optic recording and reproducing device for storing information on and reproducing information from a magneto-optic record medium, said record medium having a substrate and upper and lower magneto-optic thin films formed on opposed major surfaces of said substrate, each of said films having an axis of easy magnetization perpendicular to said major surfaces, said recording and reproducing device comprising:
an optical head including a converging optical lens for focusing a light beam on a selected region of a selected one of said upper and lower magneto-optic thin films, said optical head having (i) a recording mode in which said focused light beam alters the structure of said selected region of said upper magneto-optic thin film to enable an externally applied magnetic field to record information on said selected region of said upper magneto-optic thin film, (ii) an erase mode in which said focused light beam alters the structure of said selected region of said upper magneto-optic thin film to enable an externally applied magnetic field to erase any information stored wherein, and (iii) a reproduce mode in which said optical head optically detects the light of said focused light beam reflected from said selected region of a selected one of said upper and lower magneto-optic thin films to generate a signal corresponding to information recorded therein;
a permanent magnet disposed in alignment with said focused light beam so that said record medium may be disposed between said optical head and said permanent magnet, with said upper magneto optic thin film adjacent said optical head and said lower magneto-optic thin film adjacent said per-manent magnet;
means operative in said recording mode to cause the intensity of said focused light beam to be sufficient to (i) heat only said selected region of said upper maqneto-optic thin film to a temperature sufficiently high to enable said permanent magnet to record information on said selected region, and to simultaneously (ii) move said permanent magnet with respect to said selected region so as to magnetically record information on said selected region; and means operative in said erase mode to cause the intensity of said focused light beam to be sufficient to (i) heat only said selected region of said upper magneto-optic thin film to a temperature sufficiently high to enable said permanent magnet to erase information on said selected region by subjecting said upper magneto-optic thin film to a magnetic field having a field strength above a critical or threshold erasing field strength and to simultaneously (ii) move said permanent magnet with respect to said selected region so as to magnetically erase information from said selected region, said critical or threshold erasing field strength being less than the coercive force of said lower magneto--optic thin film, so that said permanent magnet may erase information from said selected region of said upper magneto--optic thin film without disturbing information stored in the adjacent portion of said lower magneto-optic thin film.
an optical head including a converging optical lens for focusing a light beam on a selected region of a selected one of said upper and lower magneto-optic thin films, said optical head having (i) a recording mode in which said focused light beam alters the structure of said selected region of said upper magneto-optic thin film to enable an externally applied magnetic field to record information on said selected region of said upper magneto-optic thin film, (ii) an erase mode in which said focused light beam alters the structure of said selected region of said upper magneto-optic thin film to enable an externally applied magnetic field to erase any information stored wherein, and (iii) a reproduce mode in which said optical head optically detects the light of said focused light beam reflected from said selected region of a selected one of said upper and lower magneto-optic thin films to generate a signal corresponding to information recorded therein;
a permanent magnet disposed in alignment with said focused light beam so that said record medium may be disposed between said optical head and said permanent magnet, with said upper magneto optic thin film adjacent said optical head and said lower magneto-optic thin film adjacent said per-manent magnet;
means operative in said recording mode to cause the intensity of said focused light beam to be sufficient to (i) heat only said selected region of said upper maqneto-optic thin film to a temperature sufficiently high to enable said permanent magnet to record information on said selected region, and to simultaneously (ii) move said permanent magnet with respect to said selected region so as to magnetically record information on said selected region; and means operative in said erase mode to cause the intensity of said focused light beam to be sufficient to (i) heat only said selected region of said upper magneto-optic thin film to a temperature sufficiently high to enable said permanent magnet to erase information on said selected region by subjecting said upper magneto-optic thin film to a magnetic field having a field strength above a critical or threshold erasing field strength and to simultaneously (ii) move said permanent magnet with respect to said selected region so as to magnetically erase information from said selected region, said critical or threshold erasing field strength being less than the coercive force of said lower magneto--optic thin film, so that said permanent magnet may erase information from said selected region of said upper magneto--optic thin film without disturbing information stored in the adjacent portion of said lower magneto-optic thin film.
2. The combination according to claim 1, wherein said thin films are pre-magnetized in opposite directions with respect to each other, along said axis.
3. The combination according to claim 1, wherein said thin films are pre-magnetized in the same direction along said axis.
4. The recording and reproducing device according to claim 1,further comprising means for reversing the polarity of said permanent magnet with respect to said record medium, for recording information on or erasing information from said first-mentioned optomagnetic thin film relative to the polarity used for recording information on or erasing information from said additional magneto-optic thin film.
Applications Claiming Priority (4)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP97929/1980 | 1980-07-16 | ||
| JP9792980A JPS5724046A (en) | 1980-07-16 | 1980-07-16 | Photoelectric recording medium and its recorer and reproducer |
| JP9870880A JPS5724047A (en) | 1980-07-21 | 1980-07-21 | Recorder and reproducer |
| JP98708/1980 | 1980-07-21 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1177577A true CA1177577A (en) | 1984-11-06 |
Family
ID=26439069
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000381783A Expired CA1177577A (en) | 1980-07-16 | 1981-07-15 | Magnetooptical recording medium and recording-and- reproducing device using the same |
Country Status (2)
| Country | Link |
|---|---|
| CA (1) | CA1177577A (en) |
| GB (1) | GB2083677B (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4962492A (en) * | 1988-04-29 | 1990-10-09 | Laser Magnetic Storage International Company | Magneto-optic data recording system, actuating device therefor and method of providing same |
Families Citing this family (15)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| NL8203725A (en) * | 1982-09-27 | 1984-04-16 | Philips Nv | THERMO-MAGNETO-OPTICAL MEMORY DEVICE AND RECORD MEDIUM FOR THAT. |
| US4610009A (en) * | 1983-05-23 | 1986-09-02 | Xerox Corporation | Writing, erasing and readout system for a magneto-optic recording medium |
| NL8301916A (en) * | 1983-05-31 | 1984-12-17 | Philips Nv | THERMO-MAGNETO-OPTICAL REGISTRATION DEVICE AND REGISTRATION ELEMENT THEREFOR. |
| JPS6053863A (en) * | 1983-09-05 | 1985-03-27 | Sony Corp | Apparatus for detecting magnetizing direction of magnetic recording medium |
| JPS6055536A (en) * | 1983-09-05 | 1985-03-30 | Sony Corp | Photomagnetic device |
| JPH065585B2 (en) * | 1984-02-15 | 1994-01-19 | 株式会社日立製作所 | Magneto-optical storage device |
| DE3510620A1 (en) * | 1984-02-20 | 1986-10-02 | Olympus Optical Co., Ltd., Tokio/Tokyo | Device for the generation of a magnetic field in a recording apparatus |
| JPS6171436A (en) * | 1984-09-14 | 1986-04-12 | Hitachi Ltd | Optomagnetic recording medium |
| EP0222916B1 (en) * | 1985-04-29 | 1993-02-03 | Sony Corporation | External magnetic field reversing apparatus for photomagnetic disks |
| US4849952A (en) * | 1985-09-18 | 1989-07-18 | Canon Kabushiki Kaisha | Magnetooptical information recording apparatus having intensified magnetic flux applying means |
| EP0220023B1 (en) * | 1985-10-08 | 1993-07-07 | Sharp Kabushiki Kaisha | Optical magnetic memory device |
| US4937799A (en) * | 1985-12-13 | 1990-06-26 | Canon Kabushiki Kaisha | Method and apparatus for setting light quantity most suitable for reproducing information from an optical recording medium |
| US4701895A (en) * | 1986-03-28 | 1987-10-20 | Rca Corporation | Magnetic biasing apparatus for magneto-optic recording including a permanent magnet |
| EP0555943B1 (en) * | 1988-04-06 | 1996-06-19 | Mitsubishi Denki Kabushiki Kaisha | Optical distance detector |
| EP0435278B1 (en) * | 1989-12-29 | 1996-07-10 | Matsushita Electric Industrial Co., Ltd. | Bias magnetic field generating apparatus |
-
1981
- 1981-07-13 GB GB8121521A patent/GB2083677B/en not_active Expired
- 1981-07-15 CA CA000381783A patent/CA1177577A/en not_active Expired
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4962492A (en) * | 1988-04-29 | 1990-10-09 | Laser Magnetic Storage International Company | Magneto-optic data recording system, actuating device therefor and method of providing same |
Also Published As
| Publication number | Publication date |
|---|---|
| GB2083677A (en) | 1982-03-24 |
| GB2083677B (en) | 1985-01-23 |
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