Magneto-optical recording apparatus

Abstract: A magneto-optical recording apparatus comprises an optical head for irradiating a magneto-optical recording medium with an optical beam, and a magnetic head for applying a magnetic field to the recording medium, a core of which is made of a single crystal ferrite material. In the magneto-optical recording apparatus, an easy magnetization direction based on a magnetic anisotropy of the single crystal ferrite material making a main pole portion of the core of the magnetic head may be so arranged as to be substantially coincident with a direction of the magnetic field applied to the magneto-optical recording medium, or with a direction of magnetization caused by a coil in a coil winding portion of the core of the magnetic head.

Description: BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to a magneto-optical recording apparatus which irradiates a magneto-optical recording medium with a laser beam and applies a modulation magnetic field to the side of the medium opposite to the irradiation side thereof to conduct magneto-optical information recording. Related Background Art In the magneto-optical recording apparatus of this type, information recording is performed as follows. A laser beam emitted from a semiconductor laser is converged by an optical head into a beam spot of diameter of about 1 µm to irradiate for example a magneto-optical recording medium of disk, and an external modulation magnetic field is applied at a position corresponding to the irradiation position through a magnetic head in a direction normal to the magneto-optical recording medium. A main part of such a magneto-optical recording apparatus is structured for example as shown in Fig. 1. There is a recording layer 2 of vertical magnetization film in the upper portion of the disk magneto-optical recording medium 1. A magnetic head 3 is disposed to face the recording layer 2 above the magneto-optical recording medium 1 as movable in a tracking direction. Further, an optical head 4 is disposed to face the magnetic head 3 below the magneto-optical recording medium 1 as movable in the tracking direction and in a focusing direction. The magnetic head 3 is constituted by a U-shaped core 5, which is made of a magnetic material with a high permeability, for example, a sintered ferrite material, a coil 6 wound around a main pole portion of the core 5, and a slider 7 for floating to hold the magnetic head 3 with a slight gap to a surface of the magneto-optical recording medium. The slider 7 is made for example of a non-magnetic material such as a ceramic. In the information recording, while the recording medium 1 is rotated at a high speed, a laser beam from the optical head 4 is converged into a beam spot b of diameter of about 1 µm to irradiate the recording layer 2 so as to heat a portion thus irradiated. An electric current modulated by an information signal is supplied to the coil 6 on the magnetic head 3 to excite the core 5. Then, a vertical magnetic field c along a direction of magnetization at that moment is applied to near the beam spot b on the recording layer from the main pole portion 5p of the core 5. However, when the information recording is carried out by using the above magnetic head, the magnetic head has a great heating amount due to a material of the core generating a bias magnetic field, that is, due to a high-frequency loss peculiar to the magnetic material. The heating itself possibly deteriorates the magnetic properties and other properties, and would negatively affect the facing recording layer of the magneto-optical recording medium. In detail, in case that the core of the magnetic head is made of a polycrystal Mn-Zn ferrite material, a peculiar loss is seen if the core is excited at a high frequency. As a result, the core heats to have a change in magnetic properties, for example, a decrease in permeability, and a decrease in saturation magnetic flux density, so that a magnetic field of sufficient strength may not be applied, which results in failing a good signal recording. Also, a thermal, negative effect is a deformation of the magneto-optical recording medium. On the other hand, if a frequency of information signal is decreased in order to avoid these problems, a transfer speed of information signal cannot be increased, which is against a desire of high speed processing. Further, in order to obtain a magnetic field of sufficient strength applied using the above magnetic head, a relatively large electric current, for example, three to five times of electric current applied to a magnetic head used for a hard disk, must be supplied to the coil 6. Hence, there is a problem of an increase in dissipation power of a drive circuit supplying the electric current to the coil 6. The supply of such a large electric current restricts the upper limit of recording frequency in designing of the drive circuit for the magnetic head, which does not allow an increase of recording speed of information signal. JP-A-61 292210, JP-A-31 52709 and JP-A-26 26408 each disclose magnetic heads for conventional magnetic recording apparatuses which apply a magnetic field in a direction parallel to the surface of a recording medium. JP-A-12 17703 discloses a magnetic head for magnetooptical recording which increases the magnetic field applied to a recording medium by forming a core into a U-shape and facing the open edge parts of the core onto a recording medium. SUMMARY OF THE INVENTION The present invention has been accomplished taking the above circumstances into consideration, and is purposed to provide a magnetooptical recording apparatus in which a material for a core in a magnetic head is specified and in which a strength of a magnetic field is sufficiently enhanced using a magnetic anisotropy as compared to an amplitude of supply current. The present invention provides an apparatus as set out in claim 1. By this arrangement, in the coil winding portion or in the main pole portion of the core to generate the magnetic field, the crystal orientation (easy magnetization direction) based on the magnetic anisotropy of the single crystal ferrite material allows generation of effective and sufficient magnetic field in cooperation with the magnetization by the electric current flowing through the coil. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a schematic side view of a conventional example; Fig. 2 is a schematic side view of a main part of magnetooptical recording apparatus to show the first embodiment of the present invention; Figs. 3A and 3B are schematic side views of main part to show another embodiment of the present invention; Fig. 4 is a schematic side view to show a main part of still another embodiment of the present invention; Fig. 5 is a schematic side view to show a main part of still another embodiment of the present invention; Fig. 6 is a diagram to show a relation between a composition of ferrite single crystal according to the present invention and a magnetic anisotropy constant; Fig. 7 is a drawing to illustrate a most ideal embodiment of the present invention; Fig. 8 is a diagram to show a temperature dependency of permeability of a ferrite single crystal comprising MnO·ZnO·Fe 2 O 3 ; and Fig. 9 is a diagram to show another temperature dependency of permeability of a ferrite single crystal comprising MnO·ZnO·Fe 2 O 3 . DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention is concretely explained in the following with reference to Figs. 2, 3A, and 3B. A main part of magneto-optical recording apparatus as shown has the same structure as the conventional example as shown in Fig. 1 except for characteristics of material of the magnetic core 5. The same elements are given the same numerals as in Fig. 5, and are omitted to explain here. The magnetic core 5 according to the present invention is made of a single crystal ferrite material such as MnO·ZnO·Fe 2 O 3 . As well known, the single crystal ferrite material has a peculiar magnetic anisotropy, which is easily magnetized in a specific crystal orientation (easy magnetization direction). For example, if the single crystal ferrite material employed in the present invention is a ferrite material of cubic crystal system, the easy magnetization direction may be selectively made by changing its composition, in either one of three orientations of crystallographic axes <100>, <110>, and <111>. In this connection, the sintered ferrite materials conventionally employed as the magnetic core do not have such a magnetic anisotropy as described above. The crystallographic axis <100> is a general notation for crystallographic axes [100], [010], [001], [ 1 00], [0 1 0], and [00 1 ] in a cubic crystal system, but does not represent only one of the axes. Also, the axes <110> and <111> are respective notations similarly defined as the above <100>. A core of a single crystal ferrite having an easy magnetization direction in a direction of <100> was produced in shape as shown in Fig. 2. Comparing values measured using the core as a magnetic head with values of conventional ones, a magnetic field of desired strength was obtained with an electric current lower by 15 % and the high-frequency loss was reduced by 20 % at a frequency of 10 MHz. The present invention uses these features. A first enforceability requirement to make the present invention enforceable is that the easy magnetization direction of the single crystal ferrite material employed for the core 5 is so arranged in the main pole portion 5p of the core 5 (a portion of magnetic pole opposing to the beam spot b) as to be substantially coincident with a direction of the magnetic field applied to the recording layer 2 of the magneto-optical recording medium 1 (a direction of magnetic field generated by the main pole portion 5p). Namely, in the embodiment as shown in Fig. 2, the easy magnetization direction of the single crystal ferrite material is shown by an arrow A, which is substantially coincident with the direction of the applied magnetic field as shown by an arrow C. In this case, the strength of magnetic field generated by the main pole portion 5p is greater than that in a case not to satisfy the above requirement. Thus, even if the current supplied to the excitation coil 6 is reduced, a sufficient magnetic field may be generated, whereby the magnetic field may be efficiently applied to the magneto-optical recording medium 1. A second enforceability requirement to make the present invention enforceable is that the easy magnetization direction of the single crystal ferrite material employed for the core 5 is so arranged in the winding portion of the excitation coil 6 as to be substantially coincident with a direction of the excitation by the excitation coil 6. Namely, in the embodiment as shown in Fig. 2, the easy magnetization direction of the single crystal ferrite material as shown by the arrow A is substantially coincident with the direction of excitation caused by the excitation coil 6 as shown by the arrow B. In this case, the high-frequency loss of the ferrite single crystal is smaller than that in a case not to satisfy the above second requirement, so that the heating of the core 5 may be restricted. In this embodiment, since the excitation coil 6 is wound around the main pole portion 5p of the core, the direction (arrow C) of the magnetic field applied to the recording layer 2 of the magneto-optical recording medium 1 is originally the same as the direction (arrow B) of excitation by the excitation coil 6. Therefore, both the first and the second enforceability requirements are simultaneously satisfied in this embodiment. Figs. 3A and 3B show another embodiment, in which the coil 6 is wound around a portion of the core 5 perpendicular to the main pole portion 5p. There may be two crystal orientations selected in this embodiment. In detail, in case of Fig. 3A, the easy magnetization direction, as shown by a solid line of arrow A, is the same as the direction (arrow C)of the magnetic field applied to the recording layer 2, while the direction of excitation is directed in the horizontal direction (broken line arrow B) in the winding portion of the coil 6, which may cause a magnetic effect on the main pole portion 5p. This arrangement satisfies the above first enforceability requirement. In contrast, in case of Fig. 3B, the easy magnetization direction is chosen in the direction of solid line arrow A to be coincident with the excitation direction (arrow B) by the coil 6. This arrangement satisfies the above second enforceability requirement. It is needless to mention that either of the above cases may enjoy the same merits and advantages as the first embodiment in respect of substantial function. Concretely explained in the following in connection with a composition percentage are examples in which at least the main pole portion or the excitation coil winding portion of the core of the magnetic head is made of a single crystal of cubic crystal ferrite containing MnO·ZnO·Fe 2 O 3 as a main component. Fig. 6 shows a relation between respective composition percentages of MnO, ZnO, and Fe 2 O 3 and a first magnetic anisotropy constant K 1 (Keizo Ohta, "Magnetocrystalline Anisotropy and Magnetic Permeability of Mn-Zn-Fe Ferrites", J. Phys. Soc. Japan Vol. 18 No. 5 P 685. MAY 1963). In Fig. 6, a region I represents compositions in which the first magnetic anisotropy constant K 1 is not less than zero. In this region, the easy magnetization direction is the direction of the crystallographic axis <100>. A region II represents compositions in which a composition percentage of Fe 2 O 3 is not more than 60 mol% and the first magnetic anisotropy constant K 1 is not more than zero. In the region II, the easy magnetization direction is the direction of the crystallographic axis <111>. In the present invention, an example to satisfy the first enforceability requirement is featured as follows: At least the main pole portion 5p of the core of the magnetic head is of a single crystal of cubic crystal ferrite containing MnO·ZnO·Fe 2 O 3 as a main component; The single crystal has a first magnetic anisotropy constant K 1 not less than zero at an ordinary temperature; The crystallographic axis <100> of the single crystal is so arranged as to be substantially coincident with the direction of the above magnetic field (in the embodiment as shown in Fig. 3A, the main pole portion 5p facing the recording medium 1 has the easy magnetization direction aligned in the direction of arrow A while being substantially coincident with the direction of the magnetic field C applied). Also in the present invention, another example to satisfy the first enforceability requirement is featured as follows: At least the main pole portion of the core of the magnetic head is of a single crystal of cubic crystal ferrite containing MnO·ZnO·Fe 2 O 3 as a main component in which a composition percentage of Fe 2 O 3 is not more than 60 mol%; The single crystal has a first magnetic anisotropy constant K 1 not more than zero at the ordinary temperature; The crystallographic axis <111> of the single crystal is so arranged as to be substantially coincident with the direction of the above magnetic field. Also in the present invention, an example to satisfy the second enforceability requirement is featured as follows: At least the excitation coil winding portion of the core of the magnetic head is of a single crystal of cubic crystal ferrite containing MnO·ZnO·Fe 2 O 3 as a main component; The single crystal has a first magnetic anisotropy constant K 1 not less than zero at the ordinary temperature; The crystallographic axis <100> of the single crystal is so arranged as to be substantially coincident with the direction of excitation caused by the excitation coil (In the embodiment as shown in Fig. 3B, the core 5 has the crystallographic axis <100>, which is the easy magnetization direction, aligned in the direction of arrow A in the winding portion of the excitation coil 6 while being substantially coincident with the excitation direction B of the excitation coil 6). Further, in the present invention, another example to satisfy the second enforceability requirement is featured as follows: At least the excitation coil winding portion of the core of the magnetic head is of a single crystal of cubic crystal ferrite containing MnO·ZnO·Fe 2 O 3 as a main component in which a composition percentage of Fe 2 O 3 is not more than 60 mol%; The single crystal has a first magnetic anisotropy constant K 1 not more than zero at the ordinary temperature; The crystallographic axis <111> of the single crystal is so arranged as to be substantially coincident with the excitation direction by the excitation coil. As explained above, if the present invention is applied to the structure of the first embodiment as shown in Fig. 2, both the first and the second enforceability requirements are simultaneously satisfied. That is the case also in the embodiments as shown in Figs. 4 and 5. In the embodiment as shown in Fig. 4, the core of the magnetic head is constituted by a combination of core members shown by numerals 5a and 5b, and also has a gap portion 8 made of a non-magnetic material, forming a so-called "ring head". In the embodiment as shown in Fig. 5, the core of the magnetic head is constituted by a combination of a rod core member 5a with U-shaped core members 5b and 5c, and also has two gap portions 8 made of a non-magnetic material. In these embodiments, a ferrite single crystal with a composition in either of the regions I and II is used for the main pole portion 5p of the core, and the easy magnetization direction A is coincident with the direction C of the magnetic field applied to the recording medium 1, similarly as in the above-described embodiments. The core members 5b, 5c may be made of the same ferrite single crystal, but may be made of a polycrystal ferrite as used in the conventional examples. The present Applicant conducted an experiment using a core with a composition in the region I, for example of MnO:27 mol%, ZnO:18 mol%, and Fe 2 O 3 :55 mol%, in the structure as shown in Fig. 2. According to the experiment, the core thus made showed a decrease of 20 to 30 % in heating amount in the drive frequency of 5 to 10 MHz as compared to the cases using the conventional core of polycrystal ferrite. In case that the inductance was identical, it was confirmed that the core of the present invention assured the application magnetic field of sufficient strength with a drive current lower by about 10 %. The relation diagram (Fig. 6) presented to explain the above embodiments is an example of a ferrite single crystal. It should be noted that the ranges occupied by the regions I and II change depending upon the production conditions. Therefore, the regions I and II as shown in Fig. 6 do not limit the compositions of the present invention in a strict sense. Fig. 7 shows a most ideal embodiment of the present invention. In the most ideal embodiment, as described above, the easy magnetization direction (arrow A) is coincident with the magnetic field application direction (arrow C) in the main pole portion 5p, the easy magnetization direction (arrow A) is coincident with the excitation direction (arrow B) by the excitation coil 6, and the easy magnetization direction (arrow A) is provided along the magnetic path in the other portions of the core 5. Specifically in the cubic crystal system, there always exist a crystallographic axis <100> and a counter crystallographic axis <100> normal thereto. Thus, such an ideal mode may be attained by integral formation of U-shaped core using a single crystal ferrite having an easy magnetization direction of crystallographic axis <100>. Here, the crystallographic axis <100> is a general notation for the crystallographic axes [100], [010], [001], [ 1 00], [0 1 0], and [00 1 ] in the cubic crystal system, but does not represent only one of the directions. The direction as shown in Fig. 7 is an example thereof. The above embodiment is an example of selection of crystal orientation most preferable to achieve the object to use the magnetic anisotropy of single crystal ferrite material, to enable generation of efficient magnetic field, and to reduce the high-frequency loss. The method of selection is not necessarily limited to this example, but the crystal orientation may be selected taking into consideration a cutting machinability of the core and/or properties relating to the crystal orientation, for example, wearing properties of magnetic pole upon sliding on the magneto-optical recording medium. There are examples below explained in connection with a temperature dependency of permeability, in which at least the main pole portion or the excitation coil winding portion of the core of the magnetic head is made of a cubic crystal ferrite mainly containing MnO·ZnO·Fe 2 O 3 . There are two ways of selection possible as to the aforementioned single crystal ferrite and the easy magnetization direction thereof. The first case is that the ferrite single crystal has a temperature dependency of permeability in which a primary peak of permeability appears at a temperature above the ordinary temperature and a second peak of permeability appears at a temperature below the ordinary temperature and further that the crystallographic axis <100> is the easy magnetization direction. This is explained with reference to Fig. 8. Fig. 8 shows an example of a temperature dependency of permeability of a single crystal ferrite. A permeability curve usually has two local maxima, one on the high temperature side and the other on the low temperature side. The former is called as a primary peak and the latter as a secondary peak. The example as shown in Fig. 8 has a primary peak at a temperature higher than the ordinary temperature and a secondary peak at a temperature lower than the ordinary temperature. Such a single crystal ferrite may be produced by properly choosing a composition percentage of MnO·ZnO·Fe 2 O 3 within a range where the composition percentage of the main component Fe 2 O 3 is not less than 50 mol%. In such a single crystal ferrite, the crystallographic axis <100> is the easy magnetization direction at the ordinary temperature. To satisfy at least one of the aforementioned two enforceability requirements as explained with Fig. 2 is sufficient to enjoy the merits and advantages of the present invention, which was confirmed by an experiment. Incidentally, the ordinary temperature is generally 20 °C. Considering a change in temperature environment in the magneto-optical recording apparatus, it is preferable to use a single crystal ferrite which has a primary peak at a temperature above 60 °C and a secondary peak at a temperature below 0 °C. The second selection of the single crystal ferrite and the easy magnetization direction thereof is that the single crystal has a temperature dependency of permeability in which both a primary peak and a secondary peak of permeability appear at a temperature above the ordinary temperature and that the crystallographic axis <111> is the easy magnetization direction. This is explained with reference to Fig. 9. Fig. 9 shows another example with a temperature dependency of permeability of a single crystal ferrite. In the example as shown in Fig. 9, a permeability curve has two local maxima, which are a primary peak and a secondary peak, similarly as in the aforementioned example. The two peaks are located above the ordinary temperature. Such a single crystal ferrite may be produced by properly choosing a composition percentage of MnO·ZnO·Fe 2 O 3 within a range where a composition percentage of main component Fe 2 O 3 is not more than 60 mol%. In such a single crystal ferrite, the crystallographic axis <111> is the easy magnetization direction at the ordinary temperature. To satisfy at least one of the aforementioned two enforceability requirements as explained with Fig. 2 is effective to enjoy the merits and advantages of the present invention, which was confirmed by an experiment. Provided that the ordinary temperature is generally 20 °C as explained above, considering a change in temperature environment in the magneto-optical recording apparatus, it is preferable to use a single crystal ferrite having a primary peak and a secondary peak both above 60 °C. Explained in the following using Fig. 2 is a first structure of an example to satisfy the first enforceability requirement as explained with Fig. 2. The single crystal ferrite making the core 5 as shown in Fig. 2 has the temperature dependency of permeability as show in Fig. 8. In detail, the single crystal ferrite is chosen to have a primary peak of permeability at a temperature above the ordinary temperature and a secondary peak of permeability at a temperature below the ordinary temperature. Further, at least in the main pole portion 5p facing the recording layer 2 to apply a magnetic field, the crystallographic axis <100> is so arranged as to be aligned in the direction as shown by the arrow A in Fig. 2, and therefore as to be substantially coincident with the direction of the magnetic field as shown by the arrow C, which is generated by the main pole portion 5p and applied to the recording layer 2. Next explained is a second structure of another example to satisfy the first enforceability requirement as explained with Fig. 2. In the second structure, the single crystal ferrite making the core 5 has the temperature dependency of permeability as shown in Fig. 9. In detail, the single crystal ferrite is chosen to have a primary peak and a secondary peak of permeability both above the ordinary temperature. Further, at least in the main pole portion 5p facing the recording layer 2 to apply a magnetic field, the crystallographic axis <111> is so arranged as to be aligned in the direction as shown by the arrow A in Fig. 2, and therefore as to be substantially coincident with the direction of the magnetic field as shown by the arrow C, which is generated by the main pole portion 5p and applied to the recording layer 2. Next explained with reference to Fig. 2 is a first structure to satisfy the aforementioned second enforceability requirement as explained with Fig. 2. The single crystal ferrite making the core 5 as shown in Fig. 2 has the temperature dependency of permeability as shown in Fig. 8. In detail, the single crystal ferrite is chosen to have a primary peak of permeability above the ordinary temperature and a secondary peak below the ordinary temperature. Further, at least in the winding portion of the excitation coil 6, the crystallographic axis <100> is so arranged as to be aligned with the direction as shown by the arrow A in Fig. 2, and therefore as to be substantially coincident with the direction of the excitation as shown by the arrow B, which is caused by the excitation coil 6 in the core 5. Next explained is a second structure to satisfy the second enforceability requirement as explained with Fig. 2. In this case, the single crystal ferrite making the core 5 has the temperature dependency of permeability as shown in Fig. 9. In detail, the single crystal ferrite is chosen to have a primary peak and a secondary peak of permeability both above the ordinary temperature. Further, at least in the winding portion of the excitation coil 6, the crystallographic axis <111> is so arranged to be aligned with the direction as shown by the arrow A in Fig. 2, and therefore as to be substantially coincident with the direction of the excitation as shown by the arrow B, which is caused by the excitation coil 6 in the core 5. In the present embodiment, since the excitation coil 6 is arranged to be directly wound around the main pole portion 5p of the core 5 and to be excited, both the first and the second enforceability requirements are simultaneously satisfied. In such a ferrite single crystal, there always exist one crystallographic axis <100> and a counter crystallographic axis <100> normal thereto. Thus, if the core is shaped as in the present embodiment, it is possible that the crystallographic axis <100> is aligned in the direction as shown by an arrow D normal to the arrow A, as well as in the direction of the arrow A as shown in the drawing. As such, most of magnetic paths may be aligned along the direction of crystallographic axis <100>, which assures the greatest effect. Next explained with reference to Figs. 3A and 3B are examples in which the winding portion of the excitation coil 6 is not coincident with the main pole portion 5p of the core 5. Fig. 3A shows a first structure to satisfy the aforementioned first enforceability requirement. In the first structure, the single crystal ferrite making the core 5 has the temperature dependency of permeability as shown in Fig. 8. In detail, the single crystal ferrite has a primary peak of permeability above the ordinary temperature and a secondary peak of permeability below the ordinary temperature. Further, at least in the main pole portion 5p facing the recording layer 2 to apply a magnetic field, the crystallographic axis <100> is so arranged as to be aligned with the direction as shown by the arrow A in the drawing, and therefore as to be substantially coincident with the direction of the application magnetic field as shown by the arrow C, which is generated by the main pole portion 5p and applied to the recording layer 2. Next explained is a second structure to satisfy the first enforceability requirement. In this case, the single crystal ferrite making the core 5 has the temperature dependency of permeability as shown in Fig. 9. In detail, the single crystal ferrite is chosen to have a primary peak and a secondary peak of permeability both above the ordinary temperature. Further, at least in the main pole portion 5p facing the recording layer 2 to apply a magnetic field, the crystallographic axis <111> is so arranged as to be aligned with the direction as shown by the arrow A in the drawing, and therefore as to be substantially coincident with the direction of the application magnetic field as shown by the arrow C, which is generated by the main pole portion 5p and applied to the recording layer 2. Fig. 3B shows a first structure to satisfy the aforementioned second enforceability requirement. In the first structure, the single crystal ferrite making the core 5 has the temperature dependency of permeability as shown in Fig. 8. In detail, the single crystal ferrite is chosen to have a primary peak of permeability above the ordinary temperature and a secondary peak of permeability below the ordinary temperature. Further, at least in the winding portion of the excitation coil 6, the crystallographic axis <100> is so arranged as to be aligned with the direction as shown by the arrow A in the drawing, and therefore as to be substantially coincident with the direction of the excitation as shown by the arrow B, which is caused by the excitation coil 6 in the core 5. Next explained is a second structure to satisfy the second enforceability requirement. In this case, the single crystal ferrite making the core 5 has the temperature dependency of permeability as shown in Fig. 9. In detail, the single crystal ferrite is chosen to have a primary peak and a secondary peak of permeability both above the ordinary temperature. Further, at least in the winding portion of the excitation coil 6, the crystallographic axis <111> is so arranged as to be aligned with the direction as shown by the arrow A in the drawing, and therefore as to be substantially coincident with the direction of the excitation as shown by the arrow B, which is caused by the excitation coil 6 in the core 5. In these examples, since the main pole portion 5p of the core 5 is not coincident with the winding portion of the exciting coil 6, the aforementioned first and second enforceability requirements are not simultaneously satisfied, but a sufficient effect may be obtained with satisfaction of at least one of the requirements. Also, the entire core 5 does not necessarily have to be integrally made of a single crystal ferrite. The core 5 may be constituted by two or more members, and only a necessary member or necessary members may be made of the single crystal ferrite. Further, the shape of the core is not restricted to the U-shape. For example, as shown in Fig. 4, the core may be formed by a combination of two core members 5a, 5b with a gap 8 made of a non-magnetic material, which is a so-called ring head. Also, as show in Fig. 5, the magnetic head may be formed by a core member 5a having two core members 5b on the both sides thereof with two gaps 8. In these examples, in order to satisfy the aforementioned first enforceability requirement, the core member 5a including the main pole portion 5p is made of a ferrite single crystal having the temperature dependency of permeability as shown in Fig. 8; and the crystallographic axis <100> is so arranged as to be aligned with the direction of the arrow A in the drawing, and therefore as to be substantially coincident with the direction of the application magnetic field as shown by the arrow C, which is generated by the main pole portion 5p and applied to the recording layer 2. Alternatively, the core member 5a is made of a ferrite single crystal having the temperature dependency of permeability as shown in Fig. 9; and the crystallographic axis <111> is so arranged as to be aligned with the direction of the arrow A in the drawing, and therefore as to be substantially coincident with the direction of the application magnetic field as shown by the arrow C, which is generated by the magnetic pole portion 5p and applied to the recording layer 2. In this embodiment, since the excitation coil 6 is directly wound around the main pole portion 5p, the direction of the arrow A is coincident with the excitation direction as shown by the arrow B, whereby the aforementioned second enforceability requirement is also satisfied. Structured as the above-described embodiments, the magnetic head of the present invention can generate a magnetic field with a higher strength than those in the conventional apparatuses, and can apply a sufficient magnetic field to the magneto-optical recording medium even with a reduction in supply current to the excitation coil, whereby a dissipation power of the drive circuit of the magnetic head may be decreased. In addition, the upper limit of recording frequency may be set higher than in the conventional apparatuses, so that the recording speed of information signal by the magnetic head may be increased. Also, the high-frequency loss of the core may be restrained, whereby the change in magnetic properties, such as a decrease in permeability and a decrease in saturation magnetic flux density due to heating, can be prevented. Further, the thermal, negative effect, for example, a deformation of the magneto-optical recording medium, may be prevented. It was experimentally confirmed, using the ferrite single crystal having the temperature dependency of permeability as shown in Fig. 8 for the magnetic head shaped as shown in Fig. 2 with the crystallographic axis <100> being aligned with the direction as shown by the arrow A, that the heating amount was reduced by 20 to 30 % at a drive frequency of 5 to 10 MHz as compared to that in the conventional one using the polycrystal ferrite, and that when the inductance was kept equal a sufficient magnetic field could be generated with a drive current reduced by about 10%. The present invention was detailed above. In the magneto-optical recording apparatus according to the present invention in which a magnetic field is applied by the magnetic head to the magneto-optical recording medium to conduct the information recording, the magnetic head is provided with the core made of the single crystal ferrite material, and the core is so arranged that the crystal orientation of the single crystal ferrite material has a directional property easy in magnetization in the same direction as the excitation direction of the coil in the coil winding portion of the core in recording, or, that the crystal orientation has a directional property in the same direction as the application magnetic field in the main pole portion. By that, a sufficient vertical magnetic field may be applied to the recording layer of the magneto-optical recording medium with a low electric current, reducing the dissipation power in the electric circuit supplying the current to the coil. Also, the high-frequency loss in the magnetic head is reduced, so that, with less heating, the negative effect such as deterioration in magnetic or other properties may be avoided on the magnetic head itself, and also that the negative influence on the recording medium may be avoided. Accordingly, a power supply may be performed at a higher frequency, so that excellent effects may be attained, for example, an increase in transfer speed of information.

Claims: A magneto-optical recording apparatus comprising: a magnetic head (3) for applying a magnetic field (C) to a recording medium (1) in a direction perpendicular to the surface of the recording medium (1), characterised by the apparatus further comprising: an optical head (4) for irradiating the magnetooptical recording medium (1) with an optical beam; and wherein a core (5) of the magnetic head (3) is made of a single crystal ferrite material, and wherein at least one of (a) and (b) is present wherein (a) an easy magnetization direction (A) based on a magnetic anisotropy of said single crystal ferrite material constituting a main pole portion (5p) of said core (5) of said magnetic head (3) is so arranged as to be substantially coincident with the direction of said magnetic field (C) applied to the magnetooptical recording medium, and/or wherein (b) an easy magnetization direction (A) based on a magnetic anisotropy of said single crystal ferrite material constituting said core (5) is so arranged as to be substantially coincident with a direction of magnetization (B) caused by a coil (6) in a coil winding portion of said core of said magnetic head. A magneto-optical recording apparatus according to Claim 1, wherein at least a main pole portion (5p) of said core (5) of said magnetic head (3) is of a single crystal of cubic crystal ferrite containing MnO·ZnO·Fe 2 O 3 as a main component, said single crystal having a first magnetic anisotropy constant K 1 not less than zero at an ordinary temperature and a crystallographic axis <100> substantially coincident with a direction of said magnetic field (C). A magneto-optical recording apparatus according to Claim 1, wherein at least a main pole portion (5p) of said core (5) of said magnetic head (3) is of a single crystal of cubic crystal ferrite containing MnO·ZnO·Fe 2 O 3 as a main component in which a composition percentage of Fe 2 O 3 is not more than 60 mol%, said single crystal having a first magnetic anisotropy constant K 1 not more than zero at an ordinary temperature and a crystallographic axis <111> substantially coincident with a direction of said magnetic field (C). A magneto-optical recording apparatus according to Claim 1, wherein at least an excitation coil (6) winding portion of said core (5) of said magnetic head (3) is of a single crystal of cubic crystal ferrite containing MnO·ZnO·Fe 2 O 3 as a main component, said single crystal having a first magnetic anisotropy constant K 1 not less than zero at an ordinary temperature and a crystallographic axis <100> substantially coincident (B) with a direction of excitation caused by the excitation coil (6) wound around said winding portion. A magneto-optical recording apparatus according to Claim 1, wherein at least an excitation coil (6) winding portion of said core (5) of said magnetic head (3) is of a single crystal of cubic crystal ferrite containing MnO·ZnO·Fe 2 O 3 as a main component in which a composition percentage of Fe 2 O 3 is not more than 60 mol%, said single crystal having a first magnetic anisotropy constant K 1 not more than zero at an ordinary temperature and a crystallographic axis <111> substantially coincident with a direction of excitation (B) caused by the excitation coil (6) wound around said winding portion. A magneto-optical recording apparatus according to Claim 1, wherein at least a main pole portion (5p) of said core (5) of said magnetic head (3) is made of a single crystal of cubic crystal ferrite containing MnO·ZnO·Fe 2 O 3 as a main component and having a temperature dependency of permeability in which a primary peak of permeability appears at a temperature above an ordinary temperature and a secondary peak of permeability appears at a temperature below the ordinary temperature, said single crystal having a crystallographic axis <100> substantially coincident with a direction of said magnetic field (C). A magneto-optical recording apparatus according to Claim 1, wherein at least an excitation coil (6) winding portion of said core (5) of said magnetic head (3) is made of a single crystal of cubic crystal ferrite containing MnO·ZnO·Fe 2 O 3 as a main component and having a temperature dependency of permeability in which a primary peak of permeability appears at a temperature above an ordinary temperature and a secondary peak of permeability appears at a temperature below the ordinary temperature, said single crystal having a crystallographic axis <100> substantially coincident with a direction of excitation (B) in said excitation coil winding portion. A magneto-optical recording apparatus according to Claim 1, wherein at least a main pole portion (5p) of said core (5) of said magnetic head (3) is made of a single crystal of cubic crystal ferrite containing MnO·ZnO·Fe 2 O 3 as a main component and having a temperature dependency of permeability in which both a primary peak and a secondary peak of permeability appear at a temperature above an ordinary temperature, said single crystal having a crystallographic axis <111> substantially coincident with a direction of said magnetic field (C). A magneto-optical recording apparatus according to Claim 1, wherein at least an excitation coil (6) winding portion of said core (5) of said magnetic head (3) is made of a single crystal of cubic crystal ferrite containing MnO·ZnO·Fe 2 O 3 as a main component and having a temperature dependency of permeability in which both a primary peak and a secondary peak of permeability appear at a temperature above an ordinary temperature, said single crystal having a crystallographic axis <111> substantially coincident with a direction of excitation (B) in said excitation coil winding portion.

Inventors: ISHII KAZUYOSHI, ISHII, KAZUYOSHI, ISHII, KAZUYOSHI, C/O CANON KABUSHIKI KAISHA
Applicants: CANON KK, CANON KABUSHIKI KAISHA
Application year: 1992
Main classification: G11B11
IPC codes: G11B5, G11B11, H01F1