Magneto-optical recording device

Abstract: A magneto-optical recording device has a flying head (11) that floats over a magneto-optical disk according to the rotation of the magneto-optical disk. The flying head includes a head slider. A solid lubricant (13) is applied to the bottom surface of the head slider facing the magneto-optical disk. Since the solid lubricant makes the flying head contact with the magneto-optical disk smoothly, the scratching and wear of the magneto-optical disk and the flying head decrease. Therefore, the reliability and the durability of the magneto-optical recording device can improve. Physical protrusions and recessions or holes containing fluorocarbon oil therein may be formed instead of the solid lubricant. In this case, the contact area between the flying head and the magneto-optical disk is also smaller than the case where physical protrusions and recessions are not formed. In addition, with a configuration such that thin-film layers made of a fluorocarbon resin having an excellent lubricity are formed on both sides of the bottom surface of the head slider, since the magneto-optical disk comes into contact with the head smoothly, the reliability and the durability of the magneto-optical recording device can improve.

Description: FIELD OF THE INVENTION The present invention relates to a magneto-optical recording device through which information is recorded optically, and more particularly to a flying head for magneto-optical recording. BACKGROUND OF THE INVENTION In recent years, the research and development of magneto-optical recording media as high density and large capacity memories has been much carried out. In magneto-optical recording with magneto-optical recording media, a substrate that is made of glass, plastic, ceramic materials, etc. and is coated with a vertical magnetization film composed of metal-magnetic substance, is used as a recording medium, and information is recorded on the recording medium by switching the magnetization direction of a desired portion on the vertical magnetization film. More concretely, when recording information, first, a recording medium is initialized by applying the external magnetic field from an external magnetic field generation device to the recording medium. With this operation, the magnetization direction of the vertical magnetization film on the recording medium is made uniform either upward or downward. When the initialization is completed, a laser beam from light emitting means is irradiated on a desired recording portion of the recording medium. A temperature of the recording portion whereon the laser beam is irradiated rises, and when the temperature reaches or exceeds around the Curie point of the vertical magnetic film or its magnetic compensation point, the coercive force on the recording portion becomes zero or substantially zero. With this state, the magnetization direction is switched by applying an external magnetic field (bias magnetic field) whose magnetization direction is opposite to the set direction of the above-mentioned recording portion when initialized. The temperature of the recording portion decreases and eventually returns to the room temperature by stopping the irradiation of the laser beam on the recording portion. As described above, since the switched magnetization direction of the recording portion is kept, desired information can be recorded. When reproducing information recorded in the above-mentioned way, a linearly polarized laser beam whose power is weaker than the one used during recording is irradiated on a recorded portion, and reflected light or transmitted light from the irradiated recording portion is detected. The recorded information is reproduced by detecting the rotation angle of the polarization plane of the reflected light or transmitted light. More precisely, since the rotation angle of polarization plane varies depending on the magnetization direction of the recorded portion (magnetic Kerr effect of magnetic Faraday effect), information can be read out optically with the use of the magnetic effect. Therefore, attention has recently been focused on the technique of magneto-optical recording for realizing a rewritable large capacity memory element. For rewriting information recorded on a recording medium, the following requirements must be fulfilled. (1) Initializing the recording medium. (2) Improving an external magnetic field (bias magnetic field) generation device or a recording medium whereon information can be rewritten without performing erasing operation. To meet requirement (1), however, an initialization device is separately demanded and two magneto-optical write heads may be needed, thereby causing the number of parts to increase. That is to say, in case of erasing information with a single magneto-optical write head, the same time taken for recording is required for erasing. In the mean time, in order to meet requirement (2), the composition and the thickness of the magnetic film need to be controlled. For the above reasons, the most effective means is the improvement of an external magnetic field (bias magnetic field) generation device satisfying requirement (2). Namely, information is recorded by, for example, maintaining the output of a laser beam at a fixed level and switching an external magnetic field at high speed. To switch the external magnetic field at high speed, a coil and a coil core for generating external magnetic field must be miniaturized to a great degree, and therefore, magnetic field generation areas become smaller. As a result, a magneto-optical write head and a recording medium must come close to each other. In order to get the magneto-optical write head and the recording medium close to each other, a flying head in the shape of a slider shown in Fig. 4 has been known and adopted. The flying head comprises a head slider means 31 and a head coil means 32. As shown in Fig. 4, the head coil means 32 is formed at an edge of the head slider means 31. The bottom surface of the head coil means 32 is aligned with the bottom surface of the head slider means 31. The head coil means 32 is connected to a power source 37 that generates a magnetic field, and the direction of the generated magnetic field varies depending on the polarity of the power source 37. The head having the above configuration comes into contact with a recording medium at the time the recording medium starts rotating and stops rotating. Therefore, similar to computer hard disk cases where lubricating oil such as fluorocarbon oil is applied to the disk surface, lubricating oil 33 may be applied to a protective resin film 34 (see Fig. 4). With this application, the wear rate of the flying head and the magneto-optical recording medium can be reduced. Regarding the formation of the protective resin film 34, the protective resin film 34 is first applied to a vertical magnetization film 35 through the spin coating or other process and then hardened by an irradiation of ultraviolet light. The vertical magnetization film 35 is formed on a transparent substrate 36. The magneto-optical medium, however, is portable, and this point differs from the above-mentioned hard disk. Therefore, in case liquid lubricating oil is applied to the surface of the magneto-optical recording medium, it is difficult to keep the oil on the surface, and therefore scratches may occur on the surface due to the absence of the liquid lubricating oil. This causes the reliability of the magneto-optical recording medium to remarkably lower. Additionally, some manufacturers produce magneto-optical recording media without lubricating oil on their surface. In such a case, a problem arises, namely that the magneto-optical recording media without lubricating oil are not compatible with magneto-optical recording media produced by other manufactures. In the mean time, solid lubricating oil may be applied to a portion (the bottom surface of a head) of a flying head which comes into contact with the surface of a magneto-optical recording medium. In this way, however, solid lubricating oil to be applied to the flying head needs to have durability of some hundreds times as high as that of solid lubricating oil on the magneto-optical recording medium. Therefore, only applying lubricating oil to the flying head was not sufficient for solving the above problem. JP-A-59227065 discloses a flying magnetic head for use with a magnetic recording disc. The slider surface of the head is roughened and then coated with a solid lubricant (PTFE). The coated surface is then lapped to expose the base material ferrite. The finished slider surface therefore has PTFE partly exposed and well adhered, and friction between the head and the recording disc is reduced. The preamble of claim 1 is based on this document. JP-A-1251308 discloses a floating magnetic head which is made of polycrystalline ceramic material and which is formed with undulations in the surface to be opposed to a magnetic recording medium. The abrupt surface level changes occur at the boundaries between the polycrystals. SUMMARY OF THE INVENTION An object of the present invention is to provide a magneto-optical recording device having a flying head that can smoothly float over a magneto-optical recording medium when relative motion occurs between the magneto-optical recording medium and the flying head, and can give stable operation in a long term. In order to achieve the above object, a magneto-optical recording device according to the present invention includes a magnetic head which is supported so as to float over the surface of a moving magneto-optical medium, said magnetic head incorporating a head coil for generating an external magnetic field to be applied to the medium, and having a lower surface which in use faces said medium surface, and is characterised in that said lower surface includes physical holes containing a liquid lubricant. With the above configuration, since the flying head for magneto-optical recording smoothly makes contact with the magneto-optical recording medium, scratching and wear occur less on the magneto-optical recording medium and the flying head. As a result, the life of the flying head can be prolonged, thereby permitting the reliability of the magneto-optical recording medium to increase. In addition, in this way, as the magneto-optical recording medium is compatible with magneto-optical recording media produced by other manufacturers, a magneto-optical recording device suitable for various purposes can be provided. Physical protrusions and recessions may be formed in the lower surface of the head, the physical holes containing liquid lubricant being included in the physical protrusions and recessions. With the above configuration, the contact area between the flying head for magneto-optical recording and the magneto-optical recording medium becomes further reduced, thereby allowing the friction between them to be reduced. Consequently, scratching and wear occur remarkably less on the magneto-optical recording medium and the flying head. According to the present invention, there is also provided a method of manufacturing a head slider means having physical holes containing a liquid lubricant therein, for use in a magneto-optical recording device according to claim 1, the method comprising the steps: heating a molded product in the temperature range of 2000°C to 2200°C at atmospheric pressure, said molded product being made of a mixture of SiC fine powder and sintering agent; forming the holes on a lower surface of the head slider means by burnishing said lower surface with diamond grinding stones; and coating the lower surface with a liquid lubricant so that the liquid lubricant oozes into the holes. For a fuller understanding of the nature and advantages of the invention, reference should be made to the ensuring detailed description taken in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 to Fig. 3 explain the present invention in detail. Fig. 1 is an explanatory view of the first embodiment of the present invention illustrating a state in which a flying head for magneto-optical recording having a bottom surface on which physical holes containing liquid lubricant therein are formed floats over a magneto-optical disk. Fig. 2 is an explanatory view, included by way of background to the second embodiment of the present invention, illustrating a state in which a flying head for magneto-optical recording having the bottom surface on which physical protrusions and recessions are formed floats over a magneto-optical disk. Fig. 3 is an explanatory view of the second embodiment of the present invention illustrating a state in which a flying head for magneto-optical recording having the bottom surface provided with a sintered body having physical protrusions and recessions, and holes containing liquid lubricant therein floats over a magneto-optical disk. Fig. 4 is an explanatory view of a conventional example illustrating a state in which a flying head for magneto-optical recording floats over a magneto-optical disk having lubricating oil on the surface thereof. DESCRIPTION OF THE EMBODIMENTS [EMBODIMENT 1] An explanation of the first embodiment of the present invention with reference to Fig. 1 follows. As shown in Fig. 1, a magneto-optical disk as magneto-optical recording medium is composed mainly of a protective resin film 44, a recording film 45 and a substrate 46. The recording film 45 is formed on the substrate 46, and the protective resin film 44 is on the recording film 45 for the protection. The recording film 45 has multilayer structure, for example a transparent dielectric film, a rare earth-transition metal alloy thin-film, and a reflecting film (none of them is shown) are laminated. The protective resin film 44 protects the recording layer 45 from scratching, dust, oxidization, etc. Regarding materials for the protective resin film 44, an ultraviolet hardening resin that has the advantages of easy handling and saving processing time is used. The protective resin film 44 is formed on the recording film 45 through the spin coating or other process. More precisely, the ultraviolet hardening resin is first applied to the recording film 15, and then ultraviolet light is irradiated on the ultraviolet hardening resin to harden it and to form the protective resin film 14. As shown in Fig. 4, a flying head for magnetic recording is composed of a head slider means 41 and a head coil means 42, and the head coil is formed at an edge of the head slider means 41. The flying head is configured such that the bottom surface of the head coil means 42 is aligned with the bottom surface of the head slider means 41. The head slider means 41 is made of ceramic materials, such as SiC sintered body and Al 2 O 3 - TiC mixed sintered body. For the coil core of the head coil means 42, MnZn ferrite or other material is used. A power source 47 which generates a magnetic field is connected to the head coil means 42, and the direction of a generated magnetic field varies depending on the polarity of the power source 47. The head slider means 41 lets the flying head for magneto-optical recording float over the magneto-optical disk during rotation of the latter. The flying head of the above configuration comes into contact with the magneto-optical disk when the magneto-optical disk starts and stops rotating. The bottom surface of the head slider means 41 is provided with physical holes 43 having a depth of 10nm to 2500nm, and fluorocarbon oil such as perfluoropolyether is contained in the holes. One example of manufacturing method of the head slider means 41 is described below. First, SiC fine powder whose diameter is substantially 0.5µm and a sintering agent such as B, C, B 4 C and Al 2 O 3 are mixed and hardened into a predetermined shape by pressing, and then it is heated to 2000°C to 2200°C at atmospheric pressure and is sintered. Next, the bottom surface of the head slider means 41 is burnished with diamond grinding stones. The holes 43 having a depth of substantially 250nm are formed through this process, and the fluorocarbon oil is applied to the bottom surfaces and is contained in the holes 43. When a magneto-optical disk is placed in a magneto-optical recording device having a flying head of the above configuration, a laser beam from light emitting means (not shown) is irradiated on a desired recording portion of the recording film 45 on the magneto-optical disk. When the temperature of the desired recording portion rises and reaches or exceeds around the Curie point or its magnetic compensation point, the coercive force on the recording portion becomes zero or substantially zero. At that time, an external magnetic field (bias magnetic field) is applied to the recording portion through the head coil means 42 to switch the magnetization direction into a desired direction. The magnetization direction can be switched according to the polarity of the power source 47 of the head coil means 42. When the irradiation of the laser beam on the recording portion is stopped, the temperature of the recording portion drops and eventually returns to the room temperature. Thus, desired information is recorded as the switched magnetization direction of the recording portion is kept. As described above, in the present embodiment, the holes 43 are formed on the bottom surfaces of the head slider means 41, and the fluorocarbon oil (liquid lubricant) is applied to the bottom surfaces and is contained inside the holes. With the configuration, the fluorocarbon oil contained in the holes 43 oozes out onto the bottom surface of the head slider means 41 when the magneto-optical disk rotates. Since the oozed oil functions as lubricant, it is difficult for the head slider means 41 to come into contact with the magneto-optical disk directly, thereby allowing the friction between the head slider means 41 and the magneto-optical disk to be more reduced than the cases of EMBODIMENT 1 and EMBODIMENT 3. As a result, scratching and wear of the magneto-optical disk, the head slider means 41 and the head coil means 42 extremely decrease. The fluorocarbon oil oozes into the holes 43 again when the magneto-optical disk stops rotating. Consequently, even when a liquid lubricant such as fluorocarbon oil is used, long-time lubricating effects can be expected similar to the case where solid lubricant is used. When the depth of the holes 43 is not more than 10nm, it is difficult for a liquid lubricant such as fluorocarbon oil to ooze into the holes, while when the depth is not less than 2500nm, it is difficult for the liquid lubricant to ooze out onto the surface. Therefore, the preferable depth for the holes 43 is 10nm to 2500nm. In this embodiment, a case where the physical holes 43 are formed only on the head slider means 41 and the fluorocarbon oil is contained in the holes 43, is explained, however, the holes 43 containing the fluorocarbon oil can be formed on both the head slider means 41 and the head coil means 42. In addition, oil such as fluorosilicon oil, silicon oil, and olefin oil can be used instead of fluorocarbon oil to obtain the above effects. Before the second embodiment of the invention is discussed, the construction of another flying head, not in itself in accordance with the present invention, will be described with reference to Fig. 2. It will be appreciated that physical features of this other flying head and the resulting improved frictional characteristics can be combined with those of the above-described first embodiment. As shown in Fig. 2, a magneto-optical disk as magneto-optical recording medium is composed mainly of a protective resin film 24, a recording film 25 and a substrate 26. The recording film 25 is formed on the substrate 26 and the protective resin film 24 is on the recording film 25 for the protection. The recording film 25 has multilayer structure, for example a transparent dielectric film, a rare-earth transition metal alloy thin-film, and a reflecting film (none of them is shown) are laminated. The protective resin film 24 protects the recording layer 25 from scratching, dust, oxidization, etc. Regarding materials for the protective resin film 24, for example an ultraviolet hardening resin like EMBODIMENT 1 is used. The protective resin film 24 is formed on the recording film 25 through the spin coating or other process in a similar way to EMBODIMENT 1. As shown in Fig. 2, a flying head for magnetic recording is composed of a head slider means 21 and a head coil means 22, and the head coil means 22 is formed at an edge of the head slider means 21. The flying head is configured such that the bottom surface of the head coil means 22 is aligned with the bottom surface of the head slider means 21. Like EMBODIMENT 1, the head slider means 21 is made of ferrite or ceramic materials. For the coil core of the head coil means 22, in the same way as EMBODIMENT 1, MnZn ferrite or other material is used. A power source 27 which generates a magnetic field is connected to the head coil means 22, and the direction of a generated magnetic field varies depending on the polarity of the power source 27. During the rotation of the magneto-optical disk, the head slider means 21 lets the flying head for magneto-optical recording float over the magneto-optical disk. The flying head having the above configuration comes into contact with a magneto-optical disk when the magneto-optical disk starts and stops rotating. On the bottom surfaces of the head slider means 21 and the head coil means 22, physical protrusions and recessions 23 whose maximum height R MAX is 100nm to 2500nm are formed. Table 1 shows the relation between the maximum height R MAX of the physical protrusions and recessions 23 and the coefficient of static friction µ s between a magneto-optical disk and the head slider means 21. When the maximum height R MAX is less than 100nm, the coefficient of static friction µ s rises rapidly, while when the maximum height is not less than 100nm, the coefficient of static friction µ s decreases gradually as the maximum height R MAX increases. Generally, when the coefficient of static friction µ s increases, scratching and wear tend to occur more on the magneto-optical disk, thus the preferable maximum height R MAX is at least 100nm. On the contrary, if the maximum height R MAX is not less than 2500nm, floating height becomes too small. Therefore, the preferable maximum height R MAX for the physical protrusions and recessions 23 is 100nm to 2500nm. MAXIMUM HEIGHT R MAX COEFFICIENT OF STATIC FRICTION µ s 50nm 1.60 100nm 0.43 2500nm 0.37 The physical protrusions and recessions 23 are formed in the following way. First, the bottom surfaces of the head slider means 21 and the head coil means 22 are burnished with a lapping paper with diamond abrasive grains having a fineness of not less than #4000 mesh. Then the surfaces are burnished with a lapping paper using less finer diamond abrasive grains having a fineness of, for example, not less than #400 to #4000 mesh, so that physical protrusions and recessions 23 of a preferable maximum height R MAX are formed. The physical protrusions and recessions 23 can be formed in any shape. When a magneto-optical disk is placed in a magneto-optical recording device comprising a flying head of the above configuration, a laser beam from light emitting means (not shown) is irradiated on a desired recording portion of the recording film 25 on the magneto-optical disk. When the temperature of the recording portion reaches or exceeds around the Curie point or its magnetic compensation point, the coercive force on the recording portion becomes zero or substantially zero. At this time, an external magnetic field (bias magnetic field) is applied to the recording portion through the head coil means 22 to switch the magnetization direction into a desired direction. The magnetization direction can be switched according to the polarity of the power source 27 of the head coil means 22. When the irradiation of the laser beam on the recording portion is stopped, the temperature of the recording portion falls and eventually returns to the room temperature. Thus, desired information is recorded by keeping the switched magnetization direction of the recording portion. As described above, the physical protrusions and recessions 23 whose maximum height R MAX is 100nm to 2500nm are formed on the bottom surfaces of the head slider means 21 and the head coil means 22. As a result, the contact area between the head slider means - head coil means 22 and the magneto-optical disk becomes smaller, and the friction between them can be reduced. Therefore, scratching and wear occur less on the head slider means 21 and the head coil means 22, and a floating operation of the head can be carried out smoothly at the time the magneto-optical disk starts rotating. The contact area does not mean an apparent contact area but a true contact area. With a true contact area A and the shear strength of a true contact area σ, a frictional force F is as follows: F = σ · A. Therefore, if the shear strength is constant, friction force decreases as the true contact area becomes smaller, i.e., the head slider means 21 and the head coil means 22 smoothly come into contact with the magneto-optical disk. In the above head, the physical protrusions and recessions 23 are formed on both the head slider means 21 and the head coil means 22, however, they may be formed only on the head slider means 21. In the above EMBODIMENT 1, a flying head whose bottom surface is provided with holes to which liquid lubricant is applied and the liquid lubricant is contained in the holes (Fig. 1) was described. [EMBODIMENT 2] In order to obtain a better lubricity due to the synergistic effect, the following head according to the second embodiment can be employed: a flying head having a bottom surface 63 provided with physical protrusions and recessions on the above-mentioned sintered body comprising holes, liquid lubricant that is contained in the holes (Fig. 3). Regarding the elements of Fig. 3 which have the same functions as the members of Fig. 1, for convenience' sake, the same reference numbers are given to them and the detailed explanations are omitted here. In EMBODIMENTS 1 and 2 described above, a flying head for magneto-optical recording which is mounted on a magneto-optical recording device is explained; however, the present invention can be adopted for the flying heads employed in other magneto-optical recording devices or other devices in which compatible disks are used. As a result, the life of the flying head for magneto-optical recording can be prolonged, causing the reliability of the magneto-optical recording device to increase. In addition, the present invention is compatible with magneto-optical recording media produced by other manufacturers, so that a magneto-optical recording device suitable for various purposes can be offered. As described above, a magneto-optical recording device comprising a flying head for magneto-optical recording of the present invention is configured such that holes containing liquid lubricant therein and possibly also physical protrusions and recessions are formed on the bottom surfaces of the head coil means and the head slider means of the flying head which come into contact with a magneto-optical recording medium, or at least on the bottom surface of the head slider means. Thus, since the contact area between the flying head for magneto-optical recording and the magneto-optical recording medium becomes smaller than the case where the holes are not formed, and since the liquid lubricant oozes out of the holes, in use, the friction between the flying head and the recording medium can be diminished. As a result, the scratching and wear of the magneto-optical recording medium and the flying head can be further reduced. The invention being thus described, it will be obvious that the same may be varied in many ways without departing from the scope of the invention as defined in the appendant claims.

Claims: A magneto-optical recording device wherein a magnetic head (41,42) is supported so as to float over the surface of the moving magneto-optical medium (44 to 46), said magnetic head incorporating a head coil for generating an external magnetic field to be applied to the medium, and having a lower surface which in use faces said medium surface, characterised in that said lower surface includes physical holes (43) containing a liquid lubricant. A magneto-optical recording device according to claim 1 wherein said magnetic head comprises a head slider part (41) and a head coil part (42), said lower surface of said magnetic head comprising aligned lower surface portions of said head slider and head coil parts, at least the lower surface portion of said head slider part including said physical holes. A magneto-optical recording device according to claim 2 wherein said lower surface portion of said head coil part also includes said physical holes. A magneto-optical recording device according to any of claims 1 to 3 wherein said holes have a depth of 10 nm to 2500 nm. A magneto-optical recording device according to claim 4 wherein said holes have a depth of approximately 250 nm. A magneto-optical recording device according to any of claims 1 to 4 wherein said lower surface includes physical protrusions and recessions and wherein said physical holes containing liquid lubricant are included in said physical protrusions and recessions. A magneto-optical recording device according to claim 6 wherein the maximum height of said physical protrusions and recessions is in the range of 100 nm to 2500 nm. A magneto-optical recording device according to any preceding claim wherein the liquid lubricant is fluorocarbon oil, fluorosilicon oil, silicon oil or olefin oil. A magneto-optical recording device according to claim 8 wherein the liquid lubricant is perfluoropolyether. A method of manufacturing a head slider means having physical holes containing a liquid lubricant therein, for use in a magneto-optical recording device according to claim 1, the method comprising the steps: heating a molded product in the temperature range of 2000°C to 2200°C at atmospheric pressure, said molded product being made of a mixture of SiC fine powder and sintering agent; forming the holes on a lower surface of the head slider means by burnishing said lower surface with diamond grinding stones; and coating the lower surface with a liquid lubricant so that the liquid lubricant oozes into the holes.

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: 1991
Main classification: G11B11
IPC codes: G11B11, G11B5, G11B33, G11B23