Magnetooptical recording medium with overwrite capabilities and method for using the same

#1. Field of the Invention

#The present invention relates to a magnetooptical recording medium with overwrite capabilities and a magnetooptical reproduction method for using such a magnetooptical recording medium. More specifically, the present invention relates to a process for writing over existing or previously recorded information on a magnetooptical recording medium by irradiating the medium while modulating pulses of a laser beam in accordance with the information to be recorded thereon, without modulating the orientation or strength of the magnetic recording bias field Hb.

#As used herein, the term "overwrite" refers to the action of recording new information on a recording medium without first erasing existing or previously recorded information. Thus, it is necessary that the previous information not be reproduced. More specifically, the term "overwrite" as used herein refers to the described process of writing over the previously recorded information on a magnetooptical recording medium.

#FIG. 1 is a vertical cross-sectional view of a recording medium created in accordance with a first embodiment of the present invention.

#FIG. 2 is a perspective view explaining the overwrite recording principle used in the recording medium created in accordance with an embodiment of the present invention.

#FIG. 3 is a summary drawing explaining the reproduction principle of the present invention.

#The magnetooptical recording medium of the present invention and used with the present magnetooptical recording and reproduction method, may be composed of either one or a plurality of groups of layers having perpendicular magnetic properties (hereinafter referred to as perpendicular magnetic layers). It is on these layers where recording of information takes place. The magnetic layers may be made, for example, of a substance exhibiting a vertical magnetic anisotropy and a magnetooptical effect. Preferably, the magnetic layers may be made from an amorphous magnetic alloy of a rare earth element and a transition metal element. For example, the magnetic layers may be made from magnetic alloys including, but not limited to, GdFe, GdCo, GdFeCo, TbFe, TbCo, TbFeCo, DyFe, GdTbFe, TbDyFe, GdTbCo, DyFeCo and GdTbFeCo.

#Preferably, the magnetooptical recording medium has a disk shape. The perpendicular magnetic layers generally have concentric circular or spiral-shaped tracks, on which information may be recorded. The tracks may generally be of two types, namely those that are explicitly formed in the magnetic layer and those that are implicitly formed in the magnetic layer. In disks having explicitly formed tracks, the tracks on which the information is recorded are in a curled shape or in the form of concentric circles when viewed from a direction perpendicular to the plane of the disk. Furthermore, a groove is provided between two adjacent tracks for the purpose of tracking and separation. Thus, the grooves may also be in the form of a spiral-shaped curve or concentric circles. The area between two adjacent grooves is referred to as a "land." In actuality, the relationship between lands and grooves is reversed on the back surface of the disk. Thus, the area on the side of the disk toward the direction from which a laser beam is incidental is called a groove, and that on the opposite side is called a land. The perpendicular magnetic layers may thus be formed as one surface over both the grooves and the lands. In embodiments, it is equally appropriate to make either the grooves or the lands the tracks on which the information is recorded. There is no specific relationship in size between the groove width and land width.

#In this way, lands formed in a spiral shape or in the shape of concentric circles, and grooves between each neighboring pair of lands are provided on the surface of the substrate. The perpendicular magnetic layers may then be formed as thin layers on such a substrate. Therefore, the perpendicular magnetic layers have both lands and grooves.