OVERWRITE TYPE MAGNETOOPTICAL RECORDING APPARATUS

Abstract: The magnetooptical recording unit includes a moving mechanism (22a) which can displace initial auxiliary field application unit (22), is necessary for the overwrite recording medium but detrimental to the non-overwrite recording medium, to a first or second position. The auxiliary field application with applies an initial auxiliary field to the recording medium at the first position corresponding to overwriting but does not apply the initial auxiliary field to the recording medium at the second position corresponding to non-overwriting. Information can be recorded by a single apparatus independently of whether recording medium is of the overwrite type of of the non-overwrite type.

Description: Technical Field The present invention relates to an over-write opto-magnetic recording apparatus which is capable of over-writing information by light-intensity modulation alone without requiring modulation of direction of the recording magnetic field Hb. Background Art In recent years, efforts have been directed towards development of opto-magnetic recording/reproducing method which would satisfy various requirements such as higher recording density, greater storage capacity, higher access speed and higher recording/reproducing speed, as well as development of recording apparatus, reproducing apparatus and recording medium which would be used in carrying out such an opto-magnetic recording/reproducing method. Among a variety of optical recording/reproducing methods, opto-magnetic recording/reproducing method is most promising because of its unique: namely, erasion of recorded information and recording of new information after erasion which enables repeated use of the recording medium. When a recording medium after a recording is to be used again, it is necessary that (i) the medium is initialized by an initialising device, (ii) that a recording apparatus is provided with an eraser head similar to that of the recording head or (iii) that erasing operation is conducted as a preparatory step by a recording device or an erasion device. Thus, it has been considered that opto-magnetic recording system cannot conduct over-writing of information, i.e., recording of new information regardless of whether the recording medium has an information recorded therein. Over-writing would be possible if the direction of the recording magnetic field Hb can be freely modulated between "direction A" and "direction counter to A" is possible. However, it is impossible to modulate the direction of the recording magnetic field Hb at high speed. For instance, when the recording magnetic field Hb is given by a permanent magnet, it is necessary to mechanically invert the orientation of the magnet at a high speed. This, however, is practically impossible. This problem is encountered also when the recording magnetic field Hb is given by a solenoid, because it is impossible to modulate the direction of the large current at such a high speed. Under these circumstances, as a fruit of the current remarkable progress in technology, an opto-magnetic recording method has been developed which enables over-writing solely by modulating the intensity of recording light in accordance with the binary information to be recorded, without requiring the magnetic field Hb to be turned on and off or direction-modulated, as well as an over-writable recording medium and recording apparatus which enables such over-writing, as disclosed in Japanese Patent Unexamined Publication No. 62-175948, against which Claim 1 is characterised. One of the features of this known technique resides in the use of an opto-magnetic recording medium made of a laminated vertical magnetization film of two-layered structure composed of a recording layer (first layer) and an auxiliary recording layer (second layer). The information is recorded in the first layer and also in the second layer as required, with a bit having "A direction" and a bit having "counter A direction". This known over-writing method has the following steps: (a) to move the recording medium (b) applying an initial auxiliary field Hini so as to orient the magnetization of the second layer in the "A direction" while maintaining the magnetization of the first layer unchanged until the recording is conducted; (c) irradiating the medium with a laser beam; (d) pulse-modulating the intensity of the beam in accordance with the binary information to be recorded; (e) applying, when the medium is irradiated with the beam, a recording magnetic field to the irradiated portion of the recording medium; and (f) forming, when the intensity level of the pulse beam is high, one of a bit having the "A direction" and a bit having the "counter A direction", while forming the other bit when the level of intensity of the pulse beam is low. The recording with this opto-magnetic recording method is carried out by using, for example, an over-writable opto-magnetic recording apparatus having the following features: means for moving an opto-magnetic recording medium; means for applying an initial auxiliary magnetic field Hini; a laser beam source; modulation means for modulating the beam intensity in accordance with the binary information to be recorded into a pulse having, (1) a high level which heats the recording medium to a temperature suitable for forming one of a bit having "A direction" and a bit having "counter A direction"; and a low level which heats the recording medium to a temperature suitable for forming the other of the bits.; and recording field application means which may be used also as the initial auxiliary magnetic field application means. The laser beam is modulated into pulses in accordance with the information to be recorded. The light intensity modulation into pulses itself is a known technique which is used in known opto-magnetic recording method. Means for intensity-modulating a beam into pulses in accordance with the binary information to be recorded also has been known. Such means is described, for example, in THE BELL SYSTEM TECHNICAL JOURNAL, Vol. 62 (1983), 1923-1936. The modulation means, therefore, can easily be obtained by partially modifying conventional modulation means if the required values of the high and low levels are known. Such a modification will be easy for those skilled in the art if the high and low levels are given. One of the critical features of the above-mentioned known technique resides in the values of the high and low levels of the beam intensity. Namely, the high level of the pulse beam intensity enables the recording magnetic field Hb to reverse the "A direction" magnetization of the auxiliary recording layer (second layer) into "counter A direction", and the "counter A direction" magnetization thus developed in the second layer forms in the recording layer (first layer) a bit having "counter A direction" magnetization [or "A direction" magnetization]. When the beam intensity level is low, the "A direction" magnetization in the second layer forms in the first layer a bit of "A direction" magnetization [or "counter A direction" magnetization]. In this specification, expressions OOO [or ▵▵▵] are often used for alternative reading. When OOO outside [ ] is read first, OOO outside [ ] should be selected in the subsequent occurrences. Conversely, when ▵▵▵ in [ ] is read first, ▵▵▵ inside [ ] should be read in the subsequent occurrence. As is well known, it is an ordinary measure to maintain the laser beam on at a very low level even when recording is not to be conducted, for the purpose of, for example, making an access to a predetermined recording position on the medium. Laser beam of a very low level also is used in the case where reproduction relies upon the laser beam. Maintaining the laser beam at such a very low level is conducted also in the present invention. The aforementioned low level of the beam intensity for forming a bit, however, is higher than such a very low level. Thus, the laser beam has an output waveform as shown, for example, in Fig. 1. The recording beam may consist of two beams which are in the close proximity of each other: more specifically, a non-modulated leading laser beam of a low level intended for eras ion and a trailing beam modulated in accordance with the information to be modulated for the purpose of recording. The trailing beam is modulated to have a high level and a base level which may be zero level or a level equal to or lower than the low level of the leading beam. Thus, the output waveform is as shown in Fig. 2. The medium used in the above-described known technique is sorted into two types: namely, a first form and a second form. In each case, the recording medium has a laminated structure composed of a recording layer (first layer) and an auxiliary recording layer (second layer) as shown in Fig. 3. The first layer is a recording layer which exhibits a high coercive force at room temperature and also a low magnetization inversion temperature. On the other hand, the second layer is an auxiliary recording layer which exhibits a relatively low coercive force at room temperature and also a high magnetization inversion temperature. Each of the first and second layers itself may have a laminated structure. A third layer may exist between the first layer and the second layer. Even such a medium can be used that does not have distinctive border between the first and second layers, i.e., a medium in which the first layer is progressively changed into the second layer. The recording medium of the first form satisfies the following formula 1 and meets the requirements of the formulae 2 to 5 at room temperature. T R < T C1 ≈T L < T C2 ≈T H formula 1 H C1 > H C2 + |H D1 ∓H D2 | formula 2 H C1 > H D1 formula 3 H C2 > H D2 formula 4 H C2 +H D2 < |Hini.| < H C1 ±H D1 formula 5 where, H C1 and H C2 represent the coercive forces of the recording layer (first layer) and the auxiliary recording layer (second layer), T C1 , T C2 represent the Curie points of the first layer and the second layer, T R represents the room temperature, T L and T H represent the temperatures of the recording medium when irradiated by a laser beam of low level and a laser beam of high level, and H D1 and H D2 respectively represent the coupling magnetic fields received by the first layer and the second layer, respectively. In the formulae shown above, a symbol ≈ represents "equal" or "substantially equal". In the symbols ± and ∓, + and - appearing at the upper part apply to a later-mentioned A-type (Anti-parallel type) medium, while - and + appearing at lower side apply to a later-mentioned P-type (Parallel type) medium. Ferromagnetic recording medium belongs to P type. Fig. 4 is a graph showing, in thin and fat lines, the relationship between the coercive force and the temperature as observed with the first layer and the second layer, respectively. When the initial auxiliary magnetic field (Hini,) is applied to this recording medium at the room temperature, reversing of magnetization takes place only in the second layer, i.e., the direction of magnetization of the first layer is not changed. It is therefore possible to magnetize only the second layer in the "A direction" by applying the initial auxiliary magnetic field Hini. to this recording medium. As will be seen from the formula (4), the magnetization of the second layer is held without reversing again, even when the initial auxiliary magnetic field Hini. is reduced to zero. Fig. 5 shows the concept of the state of the recording medium in which only the second layer has been magnetized to "A direction" by the initial auxiliary magnetic field Hini. In the drawings, the "A direction" and the "counter A direction" are respectively shown by upward and downward arrows. Referring to Fig. 6, the direction * of magnetization in the first layer represents the information which has been recorded. In the following description, the recorded information is expressed by X because the direction in this case has no significance. In state 1, a laser beam of a high level is applied to raise the medium temperature to T H . Since the temperature T H is higher than the Curie point T C1 , the magnetization of the recording layer (first layer) is extinguished. In addition, the magnetization of the auxiliary recording layer (second layer) also is extinguished substantially completely because the temperature T H is near the Curie point T C2 of the second layer. A recording magnetic field Hb is then applied. The direction of the magnetic field is "A direction" or "counter A direction", depending on the type of the recording medium. The recording magnetic field Hb may be a floating magnetic field which floats from the medium. For the purpose of simplification of the description, it is assumed here that the recording magnetic field Hb applied is of the "counter A direction". In this case, since the medium is moving, the irradiated portion of the recording medium is immediately moved part form the laser beam so as to be cooled. When the temperature of the medium is lowered in the presence of the recording magnetic field Hb, the magnetization of the second=d layer is inverted by the magnetic field Hb so as to become magnetization of "counter A direction" (State 2 H ). As the heat radiation proceeds to lower the medium temperature below T C1 , the magnetization of the first layer starts to appear again. In this case, the direction of magnetization of the first layer is influenced by the direction of the magnetization of the second layer due to magnetic coupling (exchanging coupling). In consequence, magnetization of the "counter A direction" (in case of the medium being of P type) or "A direction" (in case of the medium being of A type) is generated in the first layer, depending on the type of the medium (State 3 H ). This change in the state caused by the laser beam of high level will be referred to as "high-temperature cycle", hereinafter. Subsequently, laser beam of the low level is applied in the state 1 to as to raise the medium temperature to T L . Since the temperature T L is near the Curie point T C1 , the magnetization of the first layer is extinguished substantially completely as will be seen from Fig. 7. However, the magnetization of the second layer is not extinguished because the temperature T L is lower than the Curie point T C2 of the second layer (State 2 L ). In this state, the recording magnetic field Hb is maintained in the same condition as that in the high-temperature cycle, because it is impossible to turn the recording magnetic field on and off at high speed, although the magnetic field Hb is unnecessary in this step. The coercive force H C2 , however, still remains large so that the magnetic field Hb does not cause inversion of magnetization in the second layer. Since the medium is moving, the irradiated portion of the medium is immediately moved apart from the laser beam and cooled. As the cooling proceeds, the magnetization of the first layer appears again. The direction of the appearing magnetization is influenced by the direction of magnetization of the second layer due to the magnetic coupling. Inconsequence, magnetization of the "A direction" (in case of the medium being of P type) or "counter A direction" (in case of the medium being of A type) appear depending on the type of the medium. This magnetization is never changed even when the temperature is lowered to the room temperature (State 3 L ). This change in the state caused by the low-level laser beam will be referred to as "low-temperature cycle", hereinafter. As will be understood from the foregoing description, the high-temperature cycle and the low-temperature cycle produce bits of opposite magnetization directions, regardless of the initial magnetization direction of the first layer. This means that over-writing is possible by modulating a laser beam between the high level (high-temperature cycle) and the low-level (low-temperature cycle) into pulses in accordance with the information to be recorded. Although omitted from the foregoing description for the purpose of simplification, there is a medium composition which has a compensation temperature T comp between the Curie point and the room temperature. Such a medium exhibits opposite directions of magnetization at both sides of the compensation temperature T comp . When such a medium is used, therefore, the direction of application of the recording magnetic field Hb is reverse to the direction of magnetization exhibited at the room temperature by the bit formed in the high-temperature cycle. In general, the recording medium is a disk so that it is rotated during recording. Therefore, the recorded portion (bit) is subjected again to the initial field Hini. during one full rotation of the disk, so that the magnetization of the auxiliary recording layer (second layer) is aligned in the original direction, i.e., the "A direction". The magnetization of the second layer, however, does not affect the recording layer (first layer) at the room temperature, so that the recorded information is maintained unchanged. When a linear polarized light is applied to the first layer, the light reflected from the first layer contains the recorded information, so that reproduction can be conducted in the same way as that used in ordinary opto-magnetic recording medium. According to the composition design of the first and second layers, such a method is possible that the information is transferred from the first layer to the second layer which has been aligned in the original "A direction" magnetization by application of a reproduction magnetic field H R in advance of the reproduction, or a method in which the information of the first layer is naturally transferred to the second layer as soon as the influence of Hini. is eliminated, without requiring application of the reproduction magnetic field H R . In such a case, the information is reproduced from the second layer. The vertical magnetization film constituting the recording layer (first layer) and the auxiliary recording layer (second layer) are made of a material which is selected from a group consisting of amorphous or crystalline phases of (1) ferro- or ferri-magnetic substances having a Curie point but no compensation temperature and (2) ferri-magnetic substances having both a compensation temperature and Curie point. The first form of the recording medium described hereinbefore makes use of the Curie point as the magnetization inverting temperature. A description will be given of the second form of the recording medium which makes use of the coercive force H C which has been reduced at a predetermined temperature higher than the room temperature. The principle of the second form of the recording medium will be easily understood when the temperature T S1 at which the recording layer (first layer) is magnetically coupled to the auxiliary recording layer (second layer) and the temperature T S2 at which the second layer is inverted by Hb are used, respectively, in place of the Curie points T C1 and T C2 of the first and second layers in the first embodiment. The recording medium of the first form satisfies the following formula 6 and meets the requirements of the formulae 7 to 9 at room temperature. T R < T S1 ≈T L < T S2 ≈T H formula 6 H C1 > H C2 + |H D1 ∓H D2 | formula 7 H C1 > H D1 formula 8 H C2 > H D2 formula 9 H C2 +H D2 < |Hini.| < H C1 ±H D1 formula 10 where, H C1 and H C2 represent the coercive forces of the recording layer (first layer) and the auxiliary recording layer (second layer), T S1 represents the temperature at which the recording layer is magnetically coupled to the auxiliary recording layer, T S2 represents the temperature at which the second layer is inverted by Hb, respectively, T R represents the room temperature, T L and T H represent the temperatures of the recording medium when irradiated by a laser beam of low level and a laser beam of high level, and H D1 and H D2 respectively represent the coupling magnetic fields received by the first layer and the second layer, respectively. In the formulae shown above, a symbols ± and ∓, + and - appearing at the upper part apply to a later-mentioned A-type (Anti-parallel type) medium, while - and + appearing at lower side apply to a later-mentioned P-type (Parallel type) medium. Both in the first and second forms of the recording medium, the recording layer (first layer) and the auxiliary recording layer (second layer) are preferably made of an amorphous ferri-magnetic material selected from the group consisting of alloy compositions of transition metals, e.g., Fe, Co and so forth, and heavy rare earth metals, e.g., Gd, Tb, Dy and so forth. When both the first and second layers are made of a material selected from a group consisting of alloy compositions of transition metals and heavy rare earth metals, the direction and magnitude of magnetization appearing to the outside are determined by the direction and magnitude of the spin of the transition metal (referred to as "TM") in the alloy and those of the spin of the heavy rare earth metal (referred to as "RE") in the alloy. The vector representing the direction and magnitude of the whole alloy are represented by the sum of the vectors representing the directions and magnitudes of the spins of TM and RE. In the alloy, however, the directions of the vectors of spins of the TM and the heavy RE are opposite to each other, due to interaction between both spins. Therefore, the vector of the alloy, i.e., the magnitude of magnetization appearing to the outside, is zero when both vectors are equal in the magnitude. The alloy composition at which the externally recognized vector of alloy is zero is referred to as "compensation composition", hereinafter. When the composition is other than the compensation composition, the alloy has a vector of an intensity equal to the difference between the intensities of both spins and the direction which is the same as the greater one of these two vectors. The magnetization of this vector appears to the outside. When there is a difference in the intensity between TM spin and the RE spin in an alloy composition, the alloy composition is referred to as TM-rich or RE-rich composition, depending on whether the intensity of the TM spin or the intensity of the RE spin is greater. Each of the first and the second layers can be sorted into TM-rich and RE-rich types. The known mediums, therefore, can be sorted into the following four quadrants, representing the composition of the first layer by the axis of ordinate and the composition of the second layer by the axis of abscissa, as shown in Fig. 8. The P-type medium mentioned before belongs to the quadrants I and III, while the A-type medium belongs to quadrants II and IV. The points where the axes of ordinate and abscissa cross each other represents the compensation composition of both layers. Some alloy compositions exhibit a tendency that the coercive force is tentatively increased to an infinite level and then decreases before the Curie point, i.e., the temperature at which the coercive force becomes zero, is reached. The temperature which provides the infinite coercive force is referred to as compensation temperature (Tcomp). In case of TM-rich alloy compositions, no such compensation temperature exists between the room temperature and the Curie point. Any compensation temperature below the room temperature is meaningless in opto-magnetic recording. In this specification, therefore, the term "compensation temperature" is used to mean that existing between the room temperature and the Curie point. The recording medium is sorted into four types, when classified according to the presence or absence of the compensation temperature in the first and second layers. The medium of the first quadrant includes all of these four types. Figs. 9 to 12 are graphs showing the relationships between the coercive force and the temperature. In these Figures, thin and fat lines show the relationships in the first and second layers, respectively. The recording mediums are classified into the following classes, sorting first and second layers according to whether each of them is RE-rich or TM-rich and whether it has compensation temperature or not. Anyway, means for applying an initial auxiliary magnetic field Hini. is necessary in order to enable over-writing. This means is usually attached to a recording apparatus. Thus, the use of the means for applying the initial auxiliary magnetic field Hini. distinguishes the opto-magnetic recording apparatus of the invention from known opto-magnetic recording apparatus which is not able to over-write. The intensity levels (high and low levels) of the laser beam also provided distinction between the apparatus of the invention and known apparatus. This, however, does not cause critical difference because opto-magnetic recording apparatus are generally designed to allow readjustment of the intensity level of the laser beam at the place of use. It is to be understood that the provision of Hini. applying means in non-over-writing known opto-magnetic recording apparatus is not necessary and, moreover, harmful. This is because the initial auxiliary magnetic field Hini. stronger than the recording magnetic field, when applied to a non-over-write type medium, may erase information which is to be maintained and information which has just been recorded. For these reasons, hitherto, conventional non-over-write type opto-magnetic recording apparatus and over-writable opto-magnetic recording apparatus have been designed, manufactured and used separately. From the stand point of users, however, purchasing two types of apparatus are quite unacceptable considering purchasing cost, space and maintenance cost. Users which owns only one of these two types of apparatus cannot enjoy the use of the other type of medium. SUMMARY OF THE INVENTION In accordance with the present invention there is provided a recording apparatus for recording on an over-writable opto-magnetic recording medium, which comprises a recording layer having vertical magnetization and an auxiliary recording layer having vertical magnetization, both the layers being magnetically coupled to each other, and which is capable of orienting the direction of the magnetization of the auxiliary recording layer by an applied initial auxiliary magnetic field without changing the direction of the magnetization of the recording layer, said recording apparatus comprising: rotation means for rotating an opto-magnetic recording medium; magnet means for applying said initial auxiliary magnetic field; a laser beam source; modulation means for modulating the beam intensity in accordance with the binary information to be recorded into a pulse having a high level which heats the recording medium to a temperature suitable for forming either a bit having upward magnetization or a bit having a downward magnetization and a low level for heating the recording medium to a temperature suitable for forming the other of said bits; and means for applying an unmodulated recording magnetic field; characterised in that said recording apparatus further comprises: switching means for shifting said magnet means between a first position in an over-write mode operation where said magnet means can apply the initial auxiliary magnetic field to said recording medium and a second position in a non-over-write mode operation where said magnet means does not apply the initial auxiliary magnetic field to said recording medium. The switching means may or may not be provided with a power source for shifting the initial auxiliary magnetic field applying means. In the latter case, the shifting is effected by manual force exerted by the user. Preferred embodiments of the invention will now be described with the reference to the accompanying drawings, wherein: Figs. 1 and 2 are graphs showing changes in beam intensities; Fig. 3 is a schematic illustration of the construction of a recording medium; Fig. 4 is a graph showing a change in the coercive force; Fig. 5 is an illustration of the directions of magnetizations in respective layers of a recording medium; Figs. 6 and 7 are illustrations of the states of change in the magnetization of the respective layers of the recording medium; Fig. 8 is a map showing types of mediums which are sorted into four quadrants; Figs. 9 to 12 are graphs showing changes in coercive forces in various types of mediums; Fig. 13 is a perspective view of a disk-type medium; Fig. 14 is a sectional view of the medium shown in Fig. 13; Fig. 15 is a perspective view showing the underside of the cartridge accommodating a medium; Fig. 16 is a perspective view showing the upper side of the cartridge; Fig. 17 is a plan view of the whole recording apparatus embodying the present invention; Fig. 18 is a schematic front elevational view of the recording device shown in Fig. 17; Fig. 19 is a sectional view as viewed in the direction of an arrow A-A; Fig. 20 is a plan view of the coil spring apparatus used in the apparatus shown in Fig. 17; Fig. 21 is a plan view of a non-over-write type cartridge; Figs. 22 and 23 are plan views of whole recording apparatus which are different embodiments of the present invention; Fig. 24 is a perspective view showing an example of an over-write type cartridge; Fig. 25 is a perspective view of a magnet apparatus; and Fig. 26 is an illustration of the positional relationship between the cartridge shown in Fig. 24 and the magnet device shown in Fig. 25. The Best Mode for Carrying Out of the Invention The present invention will be more fully understood from the following description of the preferred embodiments which are only for illustrating purpose and not intended for limiting the scope of the invention. Figs. 13 and 14 show a disk-type opto-magnetic recording medium. The disk is provided at its center with a center hub 20a which holds the medium 20. The center hub 20a is driven by a rotary shaft 21a which in turn is driven by a later-mentioned power source. In most cases, in order to facilitate handling, the medium 20 is accommodated in a cartridge case (housing) 11. The disk and the cartridge case are synthetically referred to as a cartridge 10. The cartridge case 11 has a window 11a formed in the underside thereof and a window 11b formed in the upper side thereof. The window 11a has a circular portion which is provided so as not to hamper the rotary shaft 21a when it magnetically chucks the center hub 20a and a rectangular portion which allows a magnet device 25 for applying a recording magnetic field Hb or a head (referred to also as pickup) which includes a laser beam source 23 to make access to the medium. The window 11b formed in the upper side has a rectangular form and is provided for the purpose of allowing access of the head including the laser beam source 23 or the magnet device 25 for applying recording magnetic field Hb. A shutter 12 is provided for closing the windows 11a, 11b when the recording is not conducted. The shutter 12 is slidable in the direction of arrows shown in Figs. 15 and 16 so as to open and close the windows. Fig. 17 is a schematic plan view of the opto-magnetic recording apparatus. A magnet device 22 for applying an initial auxiliary magnetic field Hini. may be a solenoid or a permanent magnet, although a permanent magnet is used in this embodiment. As shown in Fig. 19, the magnet device 22 has a substantially U-shaped cross-section and is supported by a hinge 22a so as to be pivotable in a plane which is parallel to the surface of the medium 20. In Figs. 17 to 19, the magnet device 22 is in operative position where it can apply the initial auxiliary magnetic field Hini. to the medium. The magnet device 22 is pivotally supported by a hinge 22a so that it can be swung to a retracted position shown by an imaginary line in Fig. 17 by a manual force or by means of a motor. The magnet device 22 does not apply magnetic field to the medium when it is in the retracted position. Thus, the retracted position is a position for enabling the apparatus to operate in non-over-write mode. When the magnet device 22 is in the operative position, the laser beam source 23 emits a laser beam having a high level and a low level so as to form a spot SP on the medium, in accordance with the pulse modulated output corresponding to the binary information INFO from a modulator 24 shown in Fig. 18. Preferably, the magnet device 22 is provided with a coiled spring 26 which normally urges the magnet device 22 to the operating position as shown in Fig. 20. Fig. 21 shows an example of the cartridge accommodating a medium of the type which does not enable over-writing (this type of cartridge will be referred to as "non-over-write type cartridge). The cartridge 30 of non-over-write type has a projection 33 which, when the cartridge 30 is inserted into the medium receiving opening of the apparatus, contacts the magnet device 22 which is urged to the operating position and forcibly moves it to the retracted position against the urging force of the coiled spring 26. In consequence, the medium can be used for recording without being affected by the initial auxiliary magnetic field Hini. The magnet device 22 automatically resumes the operating position when the cartridge 30 is withdrawn from the apparatus. Figs. 22 and 23 show arrangements in which the magnet device 22 is moved between the operating position and the retracted position by the power of a motor or by means of a slider 41 which slides when contacted by the projection on the cartridge. Fig. 22 shows the state in which the magnet 22 is in operating position, while Fig. 23 shows the magnet 22 in the retracted position. The cartridge of over-write type is provided with a special mark (not shown), while the cartridge of non-over-write type lacks such a mark. The apparatus has a sensor capable of sensing such a mark. When a cassette is loaded, the sensor discriminates whether the loaded cassette is of the over-write type or non-over-write type. In the former case, the slider 41 operates to bring the magnet 22 to the operative position. In the latter case, the slide 41 operates to bring the magnet device to the retracted position. Figs. 24 to 26 show a modification of the arrangement shown in Figs. 22 and 23. In this modification, the over-write type cartridge 51 is provided with a special notch 53, while the cartridge of non-over-write type lacks such a notch. The magnet device 22 has a substantially U-shaped form as shown in Fig. 25 so as to fit to the notch 53 in the cartridge case 51. Thus, the magnet device 22 is allowed to slide to the central position so as to apply the initial auxiliary magnetic field Hini. to the medium only when the cartridge is of the over-write type. In contrast, the cartridge of non-over-write type lacks the notch 53 so that the magnet 22 cannot slide is contact with the case 51. Therefore, the magnet device 22 does not apply the initial auxiliary magnetic field Hini. to the medium 20. Capability of Exploitation of the Invention As has been described, according to the present invention, there is provided an over-writable opto-magnetic recording apparatus in which an initial auxiliary magnetic field Hini. applying means, which is necessary for over-write type recording medium but harmful for non-over-write type medium, is shifted by a shifting means such that, when an over-write type recording medium is used, the initial auxiliary magnetic field applying means is set in a first position where it can apply the initial auxiliary magnetic field Hini. to the medium, whereas, when a non-over-write medium is used, the initial auxiliary magnetic field applying means is set in a second position where the initial auxiliary magnetic field is not applied to the medium. According to the invention, therefore, a single opto-magnetic recording apparatus can adapt both to mediums of over-write type and mediums of non-over-write type.

Claims: A recording apparatus for recording on an over-writable opto-magnetic recording medium (20), which comprises a recording layer having vertical magnetization and an auxiliary recording layer having vertical magnetization, both the layers being magnetically coupled to each other, and which is capable of orienting the direction of the magnetization of the auxiliary recording layer by an applied initial auxiliary magnetic field without changing the direction of the magnetization of the recording layer, said recording apparatus comprising: rotation means for rotating an opto-magnetic recording medium; magnet means (22) for applying said initial auxiliary magnetic field; a laser beam source (23); modulation means (24) for modulating the beam intensity in accordance with the binary information to be recorded into a pulse having a high level which heats the recording medium (20) to a temperature suitable for forming either a bit having upward magnetization or a bit having a downward magnetization and a low level for heating the recording medium (20) to a temperature suitable for forming the other of said bits; and means (25) for applying an unmodulated recording magnetic field; characterised in that said recording apparatus further comprises: switching means for shifting said magnet means (22) between a first position in an over-write mode operation where said magnet means (22) can apply the initial auxiliary magnetic field to said recording medium (20) and a second position in a non-over-write mode operation where said magnet means (22) does not apply the initial auxiliary magnetic field to said recording medium (20). A recording apparatus according to Claim 1, wherein said switching means shifts said magnet means (22) for applying an initial auxiliary magnetic field in a plane substantially parallel to the surface of said recording medium (20). A recording apparatus according to Claim 1 or Claim 2, wherein said switching means includes means for supporting said magnet means (22) for applying an initial auxiliary magnetic field pivotally about an end thereof. A recording apparatus according to Claim 1 or Claim 2, wherein said switching means includes means (41) for slidably supporting said magnet means (22) for applying an initial auxiliary magnetic field. A recording apparatus according to any preceding claim, further comprising means (26) for biasing said magnet means (22) for applying an initial auxiliary magnetic field toward said first position. A recording apparatus according to any preceding claim, wherein said switching means includes means (53) for discriminating if said recording medium (20) is one which is capable of over-writing or not, said magnet means (22) for applying an initial auxiliary magnetic field being positioned to said first position when said discriminating means (53) discriminates that the recording medium (20) is capable of over-writing. A recording apparatus according to Claim 6, wherein said discriminating means (53) discriminates if said recording medium (20) is capable of over-writing or not in response to the operation of the recording medium (20) when mounted on said recording apparatus.

Inventors: KAWAI TOSHIHIKO, SATO MASATOSHI, KAWAI, TOSHIHIKO, SATO, MASATOSHI
Applicants: NIPPON KOGAKU KK, NIKON CORPORATION
Application year: 1989
Main classification: G11B11
IPC codes: G11B5, G11B11, G11B19