Recording and reading method and device of magneto-optical memory elements

Abstract: A recording and reading method and device of magneto-optical memory elements are provided to record and read an information signal to and from the magneto-optical memory elements (1) containing at least two magnetic layers (3) magnetically coupled and laminated by means of a light-intensity modulated overwriting method employing a recording magnetic field and an intializing magnetic field. The recording and reading method has a feature of applying the initializing magnetic field to the magneto-optical memory elements at least one time between the point of time when setting the magneto-optical memory elements on a recording or reading position, finishing a reading or recording, and making sure of the operations such as recording or erasing and the point of time when subsequent recording begins. The recording and reading device of magneto-optical memory elements is characterized to have an electromagnet (11) served as applying a recording magnetic field to the magneto-optical memory elements and as applying an initializing magnetic field to the magneto-optical memory elements at the same position, means (13) for controlling the means for applying the recording magnetic field and the means for applying the initializing magnetic field so that the recording magnetic field is applied to the magneto-optical memory elements during recording and the initializing magnetic field is applied to the magneto-optical memory elements at least one time between the point of time when setting the magneto-­ optical memory elements on a recording or reading position, finishing a reading or recording, and making sure of the operations such as recording or erasing and the point of time when subsequent recording begins, and means for modulating intensity of a light beam in response to a recording signal.

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of and device for recording and reading of magneto-optical memory elements by means of a light-intensity modulated overwriting method. 2. Description of the Related Art A normal recording and reading device of magneto-optical memory elements, as disclosed in the Japanese Laid-Open Patent Application (KOKAI) No.62-175948 and SPIE Vol. 1078 Optical Data Storage Topical Meeting (1989) pp 258-264, is designed so that a light-intensity modulated overwriting can be carried out on a magneto-optical memory element containing a magnetic multi-layer film. The normal recording and reading device for the magneto-optical memory element includes an optical head containing an objective lens and a laser source for irradiating a laser beam to the magneto-optical memory element and modulating the intensity of the laser beam to high or low level, means for applying a recording magnetic field to the magneto-optical memory element, and means for applying an initializing magnetic field to the magneto-optical memory element. If no cover such as a cartridge case is applied to the magneto-optical memory element (for example, like a compact disc), the light-intensity modulated overwriting can be carried out by the foregoing recording and reading device. In addition, the initializing magnetic field is applied to the magneto-optical memory element all the time or only during a recording. If, however, a cover such as a cartridge case is applied to the magneto-optical memory element (for example, like a floppy disk), it is difficult to keep space which is wide enough to install both the means for applying the recording magnetic field to the magneto-optical memory element and the means for applying the initializing magnetic field to the magneto-optical memory element. because two separate means for applying magnetic fields to the magneto-optical memory element, that is, the means for applying the recording magnetic field and the means for applying the initializing magnetic field, must be included in the foregoing recording and reading device. Therefore, the light-intensity modulated overwriting cannot be carried out on a magneto-optical memory element which is accommodated in a cartridge case. SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a method of and device for recording and reading of magneto-optical memory elements which is capable of recording and reading an information signal to and from a magneto-optical memory element containing at least two magnetic layers by means of a light-intensity modulated overwriting method, even if the magneto-optical memory element is accommodated in a housing. According to a first aspect the present invention, as defined by claim 1, provides a method of recording and reading an information signal to and from a magneto-optical memory element containing at least two magnetically coupled laminated magnetic layers by means of a light-intensity modulated overwriting method employing a recording magnetic field and an initializing magnetic field, the method comprising the recording steps of: applying said recording magnetic field for recording information on the magneto-optical memory element; characterized: by applying said initializing magnetic field to said magneto-optical memory element only between each successive application of the recording magnetic field; and in that both said recording and initializing magnetic fields are applied at the same position. According to a second aspect the present invention, as defined by claim 8, provides a device for recording and reading an information signal to and from a magneto-optical memory element containing at least two magnetically coupled laminated magnetic layers by means of a light-intensity modulated overwriting method employing a recording magnetic field and an initializing magnetic field, the device comprising: means for applying, during recording of information, said recording magnetic field to said magneto-optical memory element; means for applying, during a recording operation, said initializing magnetic field to said magneto-optical memory element; means for modulating intensity of a light beam in response to a recording signal during recording; characterized: by means for controlling said magnetic field applying means and said initializing magnetic field applying means so that said initializing magnetic field is applied to said magneto-optical memory element only between each successive application of the recording magnetic field; and in that the initializing magnetic field is applied by said initializing magnetic field applying means at the same position as where said recording magnetic field applying means applies said recording magnetic field. In a third aspect, a recording and reading device in accordance with the invention is defined by claim 14. The preamble of claims 1, 8 and 14 relates to the disclosure of EP-A-0 288 069. In operation, according to the present invention, the initializing magnetic field and the recording magnetic field are applied to the same position of the magneto-optical memory element but at different times. As a result, an information signal can be recorded on a magneto-optical memory element accommodated in a housing such as a cartridge case by means of the light-intensity modulated overwriting method. Further, if the initializing magnetic field is set to be applied to the magneto-optical memory element at least one time between the point of time when setting the magneto-optical memory element on a recording or reading position, finishing a reading or recording, and making sure of the operations such as recording or erasing and the point of time when subsequent recording begins, one magnetic layer of the at least two magnetic layers of the magneto-optical memory element is left constantly initialized. This results in being able to realize the recording by means of the light-intensity modulated overwriting at any time. According to a preferred embodiment of the present invention, the recording magnetic field and the initializing magnetic field are produced by the same one electromagnet. Thus, it is possible to reduce the number of parts. In this instance, switching from the recording magnetic field to the initializing magnetic field or vice versa can be achieved by adjusting the magnitude or the direction of the current flowing through the electromagnet. BRIEF DESCRIPTION OF THE DRAWINGS Fig.1 is a view illustrating a magneto-optical memory element and a recording and reading device for the magneto-optical memory element according to a first embodiment of the invention; Fig.2 is an expanded view illustrating a portion of magnetic layers of the memory element; Fig.3 is a graph illustrating how coercivity changes with temperature in a magnetic layer; Fig.4 is a chart illustrating how intensity of a laser beam changes; Fig.5 is a diagram illustrating when an initializing magnetic field is applied to the magneto-optical memory element; and Fig.6 is a view illustrating a magneto-optical memory element and a recording and reading device for the magneto-optical memory element according to a second embodiment of the invention. DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described with reference to Fig.1 to Fig.5. Fig.1 is a view illustrating a magneto-optical memory element and a recording and reading device 7 for the magneto-optical memory element according to the first embodiment of the invention. As shown in Fig.1, magneto-optical memory element 1 is composed of a transparent enhancement layer 2 for enhancing a reading signal in a reading mode, magnetic layers 3, a protective layer 4, a protective coating layer 5, and a substrate 6 made of glass or transparent resin on which the transparent enhancement layer 2, the magnetic layers 3, the protective layer 4, and the protective coating layer 5 are laminated in the described sequence. The magneto-optical memory element 1 is accommodated in a cartridge case (not shown). Fig.2 is an expanded view illustrating a portion of the magnetic layers. Fig.3 shows a graph illustrating how coercivity changes with temperature in the magnetic layers. As shown in Fig.2, the magnetic layers 3 provide a memory layer 21 and an auxiliary layer 22. The memory layer 21 is made of such a material that has large coercivity H₁ in an ambient temperature and a relatively low Curie point T₁ (at which the coercivity becomes substantially zero). The relation between the temperature and the coercivity of the memory layer 21 is exemplified by a line I as shown in Fig.3. The auxiliary layer 22 is made of such a material that has relatively small coercivity H₂ in an ambient temperature and a higher Curie point T₂ . The relation between the temperature and the coercivity of the auxiliary layer 22 is exemplified by a line II as shown in Fig.3. Light-intensity modulated overwriting method will be described. In an initializing process, the initializing magnetic field H ini is applied in the direction shown in Fig.2 in order to initialize the magnetization of the auxiliary layer 22 in one direction, that is, the downward direction as shown in Fig.2. The magnetization of the memory layer 21 is reversed, because the coercivity H₁ is larger than the initializing magnetic field H ini as shown in Fig.3. A recording is achieved by irradiating to the magneto-optical memory element 1 a laser beam whose intensity is modulated to a high or low level as the recording magnetic field H w is being applied thereto. Fig.4 shows a chart illustrating how intensity of a laser beam changes. That is, when the high-level laser beam shown by the I level of Fig.4 is irradiated. the temperature of the memory layer 21 and the auxiliary layer 22 are both raised to a point T H which is near or higher than the Curie points T₂ and T₁ . When the low-level laser beam shown by the II level of Fig.4 is irradiated, the temperature of the memory layer 21 is only raised to a point T L which is near or higher than the Curie point T₁. As such, when the high-level laser beam is irradiated, the recording magnetic field H w reverses the magnetization of the auxiliary layer 22 in the upward direction shown in Fig.2. The direction of the magnetization of the memory layer 21 is the same as that of the magnetization of the auxiliary layer 22 by virtue of the exchange force effected on the interface in a cooling process. The magnetization of the memory layer 21 is, thus, directed upward. When the low-level laser beam is irradiated, on the other hand, the recording magnetic field H w has no effect of reversing the magnetization of the auxiliary layer 22. Like the foregoing case, the direction of magnetization of the memory layer 21 becomes the same as that of the magnetization of the auxiliary layer 22 in the cooling process. This results in directing the magnetization of the memory layer 21 downward as viewed in Fig.2. In addition, as shown in Fig.3, the recording magnetic field H w is adjusted to be much smaller than the initializing magnetic field H ini . Further, as shown by the III level of Fig.4, the laser beam intensity irradiated in a reading operation is adjusted to be much lower than that in a recording operation. A recording and reading device 7 for recording and reading an information signal to and from the magneto-optical memory element 1 by means of the light-intensity modulated overwriting method includes a spindle motor 8 for rotating the magneto-optical memory element 1 at a predetermined rotation speed, an optical head 9 having a laser source (not shown) for irradiating a laser beam to the magneto-optical memory element 1 and an objective lens 10, and a beam control unit (not shown) for modulating the intensity of the laser beam in response to a recording signal into two, high and low, levels as shown by the stages I and II of Fig.4. The recording and reading device 7, further, includes an electromagnet 11 serving as means for applying the recording magnetic field H w and the initializing magnetic field H ini , a power source 12 for applying a voltage to the electromagnet 11, and a controller 13 serving as means for controlling the quantity and direction of the current flowing through the electromagnet 11 by controlling the quantity and direction of a voltage applied from the power source 12 to the electromagnet 11 and selectively generating either one of the recording magnetic field H w and the initializing magnetic field H ini . Fig.5 shows a diagram illustrating when the initializing magnetic field H ini is applied to the magneto-optical memory element 1. The controller 13 is designed to apply the recording magnetic field H w from the electromagnet 11 to the magneto-optical memory element 1 and apply the initializing magnetic field H ini from the electromagnet 11 to the magneto-optical memory element 1 at least one time between the point of time when setting the magneto-optical memory element to a recording or reading position, finishing a reading or recording, and making sure of the operations such as recording or erasing and the point of time when subsequent recording begins as shown in Fig.5. With the foregoing arrangement, when recording an information signal on the magneto-optical memory element 1, by irradiating a high-level or low-level laser beam from the laser source and applying the recording magnetic field H w from the electromagnet 11, a desired signal is recorded on the memory layer 21 of the magnetic layers 3. The magnetization of the memory layer 21 is reversed to the opposite direction depending on the intensity level, high or low, of the laser beam as described above. By applying the initializing magnetic field H ini to the magneto-optical memory element 1 at least one time between the point of time when setting the magneto-optical memory element to a recording or reading position, finishing a reading or recording, and making sure of the operations such as recording or erasing and the point of time when subsequent recording begins, it is possible to keep the auxiliary layer 22 constantly initiated. Moreover, the present embodiment is designed to apply the recording magnetic field H w and the initializing magnetic field H ini to the same position, that is, by the one electromagnet 11. If, therefore, the magneto-optical memory element 1 is accommodated in a cartridge case, the recording magnetic field H w and the initializing magnetic field H ini are positively applied to the magneto-optical memory element 1. Further, since the one electromagnet 11 serves as means for applying the recording magnetic field H w and the initializing magnetic field H ini , it is possible to reduce the number of parts. In addition, when reading the signal, by irradiating a lower laser beam as shown by the III level of Fig.4 than that in a recording mode, the signal recorded on the memory layer 21 is allowed to be readed. Next, a second embodiment of the present invention will be described with reference to Figure.4 and Fig.6. Fig.6 is a view illustrating magneto-optical memory element and a recording and reading device 27 for the magneto-optical memory element according to a second embodiment of the invention. As shown in Fig.6, magneto-optical memory element 1 has the same arrangement as that described in the first embodiment. Herein, similar parts are referenced by similar numbers and the overlapped description is left out. Like the first embodiment, a recording and reading device 27 for recording and reading an information signal to and from the magneto-optical memory element 1 by means of the light-intensity modulated overwriting method includes a spindle motor 28 for rotating the magneto-optical memory element 1 at a predetermined rotation speed, an optical head 29 having a laser source (not shown) for irradiating a laser beam to the magneto-optical memory element 1 and an objective lens 30, and a beam control unit (not shown) for modulating the intensity of the laser beam in response to a recording signal into two, high and low, levels as shown by the stages I and II of Fig.4. The recording and reading device 27 further includes a first permanent magnet 31 serving as means for applying the recording magnetic field H w , a second permanent magnet 32 serving as means for applying the initializing magnetic field H ini , and a supporting member 33 for supporting the first permanent magnet 31 and the second permanent magnet 32 on its opposite ends. The supporting member 33 is rotatably supported by a stepping motor 34 serving as means for alternately moving the first permanent magnet 31 and the second permanent magnet 32. When the supporting member 33 is rotated 180° by the stepping motor 34, either one of the first permanent magnet 31 and the second permanent magnet 32 is selectively directed to the magneto-optical memory element 1. A power source 35 is provided for driving the stepping motor 34 and is controlled by a controller 36. The controller 36 serves as means for controlling the recording magnetic field H w and the initializing magnetic field H ini . As such, it brings the first permanent magnet 31 in opposition to the magneto-optical memory element 1 when recording an information signal. On the other hand, it brings the second permanent magnet 32 in opposition to the magneto-optical memory element 1 at least one time between the point of time when setting the magneto-optical memory element to a recording or reading position, finishing a reading or recording, and making sure of the operations such as recording or erasing and the point of time when subsequent recording begins. The recording and reading operation is not described because it is the same as that described in the first embodiment. According to the foregoing two embodiments, the magnetic layers 3 are designed to have two layers, the memory layer 21 and the auxiliary layer 22. The memory layers 3, however, may have three layers further containing a medium layer (see SPIE Vol.1078 Optical Data Storage Topical Meeting (1989) pp 258-264) for reducing the initializing magnetic field H ini between the memory layer 21 and the auxiliary layer 22. Further, the magnetic layers 3 may have four or more layers including those layers. Many widely different embodiments of the present invention may be constructed without departing from the scope of the present invention. It should be understood that the present invention is not limited to the specific embodiments described in the specification, except as defined in the appended claims.

Claims: A method of recording and reading an information signal to and from a magneto-optical memory element (1) containing at least two magnetically coupled laminated magnetic layers (3;21,22) by means of a light-intensity modulated overwriting method employing a recording magnetic field (H w ) and an initializing magnetic field (H ini ), the method comprising the recording steps of: applying said recording magnetic field (H w ) for recording information on the magneto-optical memory element; characterized: by applying said initializing magnetic field (H ini ) to said magneto-optical memory element only between each successive application of the recording magnetic field; and in that both said recording and initializing magnetic fields are applied at the same position. A method as claimed in claim 1, wherein the same one electromagnet (11) is utilized in the steps of applying the recording magnetic field and the initializing magnetic field. A method as claimed in claim 1, wherein respective different magnets (31,32) are utilized in the steps of applying the recording magnetic field and the initializing magnetic field. A method as claimed in claim 3, wherein said different magnets (31,32) are controlled to bring the desired magnet in opposition to the magneto-optical memory element according to whether the recording magnetic field or the initializing magnetic field is to be applied thereto. A method as claimed in any of claims 1 to 4, wherein said magneto-optical memory element (1) is accommodated in a cartridge case. A method as claimed in any of claims 1 to 5, wherein said at least two magnetic layers of the magneto-optical memory element comprise a memory layer (21) and an auxiliary layer (22), said memory layer (21) being made of such a material as having large coercivity in an ambient temperature and a low Curie point, and said auxiliary layer (22) being made of such a material as having small coercivity in an ambient temperature and a higher Curie point than that of said memory layer. A method as claimed in any of claims 1 to 6, wherein said magneto-optical memory element (1) consists of an enhancement layer (2), said at least two magnetic layers (3;21,22), a protective layer (4), a protective coating layer (5), and a substrate on which said enhancement layer, said magnetic layers, said protective layer, and said protective coating layer are laminated in the described sequence. A device for recording and reading an information signal to and from a magneto-optical memory element (1) containing at least two magnetically coupled laminated magnetic layers (3;21,22) by means of a light-intensity modulated overwriting method employing a recording magnetic field (H w ) and an initializing magnetic field (H ini ), the device comprising: means (11;31) for applying, during recording of information, said recording magnetic field (H w ) to said magneto-optical memory element; means (11;32) for applying, during a recording operation, said initializing magnetic field (H ini ) to said magneto-optical memory element; means (9;29) for modulating intensity of a light beam in response to a recording signal during recording; characterized: by means (13;34,36) for controlling said magnetic field applying means and said initializing magnetic field applying means so that said initializing magnetic field (H ini ) is applied to said magneto-optical memory element only between each successive application of the recording magnetic field (H w ); and in that the initializing magnetic field (H ini ) is applied by said initializing magnetic field applying means at the same position as where said recording magnetic field applying means applies said recording magnetic field (H w ). A device as claimed in claim 8, wherein said means for applying the recording magnetic field and said means for applying the initializing magnetic field comprise the same one electromagnet (11). A device as claimed in claim 8, wherein said means for applying the recording magnetic field and said means for applying the initializing magnetic field comprise respective different magnets (31,32). A device as claimed in claim 10, wherein said controlling means (34,36) is operable to bring the desired magnet (31 or 32) in opposition to the magneto-optical memory element according to whether the recording magnetic field or the initializing magnetic field is to be applied thereto. A device as claimed in claim 11, wherein the controlling means comprises a stepping motor (34). A device as claimed in any of claims 8 to 12, wherein said modulating means (9;29) is operable to set the intensity light beam at two, high and low, levels. A device for recording and reading information on a magneto-optical memory element divided into a plurality of sub-elements, each sub-element having at least two magnetically coupled magnetic layers (3;21,22), said device utilizing a light-intensity modulated overwriting recording method and comprising: initializing magnetic field means (11;32) for creating initial conditions (H ini ) in at least one of the layers of a sub-element; recording magnetic field means (11;31) for creating conditions for recording information on another of the layers of said sub-element; characterized: by means (13;34,36) for controlling the initializing magnetic field means and the recording magnetic field means in order to provide initial conditions on the at least one layer between each successive operation of the recording magnetic field means on said sub-element; and in that said initializing magnetic field means and said recording magnetic field means are applied to the same sub-element.

Inventors: KATAYAMA HIROYUKI, MIYAKE TOMOYUKI, NAKAYAMA JUNICHIRO, OHTA KENJI, KATAYAMA, HIROYUKI, MIYAKE, TOMOYUKI, NAKAYAMA, JUNICHIRO, OHTA, KENJI
Applicants: SHARP KK, SHARP KABUSHIKI KAISHA
Application year: 1990
Main classification: G11B11
IPC codes: G11B11, G11B19