Information is recorded on a magneto-optical recording medium as follows. Namely, a light beam is converged on the magneto-optical recording medium, so as to become a light spot, having a diameter of about 1 micron. As a result, the temperature of the portion of the magneto-optical recording medium on which the light spot is located, rises to a Curie point, thereby decreasing a coercive force of the portion. After that, a magnetic field is applied to the portion where the coercive force is decreased. A magnetization direction of the portion where the light spot is oriented according to the applied magnetic field and the recording of information thus performed.
There are two kinds of systems for recording information like the above i.e., the light modulation system and the magnetic field modulation system.
According to the light modulation system, information is recorded in the following manner: (1) erasure is performed by applying a magnetic field having a predetermined direction to the magneto-optical recording medium, this initialization operation causes all the recording area to have the same magnetization direction as the applied magnetic field, and thereafter (2) information is recorded, by applying a magnetic field having the opposite direction to the portion, while changing an intensity of laser light according to desired recording information, thereby forming a predetermined recording bit on the magneto-optical recording medium. In contrast, according to the magnetic field modulation system, information is recorded in the following manner: a modulated magnetic field is applied to a portion of the magneto-optical recording medium where information is to be recorded, a direction of the modulated magnetic field is changed to the opposite direction in response to recording information, thereby forming a predetermined recording bit on the magneto-optical recording medium.
A magnetic head for use in the light modulation system is required to generate a strong d.c. magnetic field from an N-pole and a S-pole of a magnet since, using the strong d.c. magnetic field from the N-pole and S-pole, information should be recorded twice on the same track for accuracy while tracing the desired track. Accordingly, a magneto-optical recording medium for use in the light modulation system which has a magnetic field between 200 Oe and 300 Oe, during recording is available in the market.
In contrast, a magnetic head for use in the magnetic field modulation systems is required to switch a modulated magnetic field at a high speed, i.e., in a short cycle on the order of 10 ns. The magnetic head is thus designed to have a low inductance. The magneto-optical recording medium for use in the magnetic field modulation system is, therefore, improved in the sensitivity for magnetic field in order to be able to record information with a magnetic field of about 150 Oe, since the magnetic head having the low inductance can generate a low magnetic field of 100 Oe to 200 Oe.
As discussed above, the functions required for the respective systems, i.e., a strong d.c. magnetic field for the light modulation system and switching the modulated magnetic field at a high speed for the magnetic field modulation system, conflict with each other. Namely, the magnetic head for use in the magnetic field modulation system cannot record information on the magneto-optical recording medium for use in the light modulation system because the intensity of the generated magnetic field from this head is too weak to record. Further, the magnetic head for use in the light modulation system cannot record information on the magneto-optical recording medium for use in the magnetic field modulation system because this head cannot reverse the modulated magnetic field at such a high speed.
As discussed above, the magnetic head for one system cannot record information on the magneto-optical recording medium used for the other system. Therefore, two kinds of magnetic heads should be prepared in a single recording and reproduction apparatus in order that the single apparatus can record information based on the respective systems such an apparatus becomes massive.
In order to solve this problem external magnetic generation apparatuses which have respective complexed magnetic heads including both a magnetic head capable of generating a strong d.c. magnetic field and a magnetic head capable of switching a modulated magnetic field at a high speed, both magnetic heads being integrated with each other, are disclosed in the Japanese unexamined patent publications No. 3-216836 and No. 3-268253. With this arrangement, the apparatus is not so massive.
However, in the respective external magnetic generation apparatuses disclosed in the publications, the magnetic heads of the complexed magnetic head differ in their power consumptions. Accordingly, the external magnetic generation apparatus is required to have two drivers, i.e., one is for the magnetic field modulation system and the other is for the light modulation system, for supplying power to the corresponding magnetic head. Namely, two drivers are required for a single apparatus, thereby making it impossible for the apparatus to be smaller although the apparatus is required to be more compact.
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