Opto-magnetic recording medium

DETAILED DESCRIPTION This invention relates to improvements in an opto-magnetic recording medium which is used in an opto-magnetic memory, a magnetic recording and displaying element or the like and which can be read out by the use of the magneto-optical effect such as the magnetic Kerr effect or the Faraday effect.
As the recording layer of an opto-magnetic recording medium, there is known a polycrystal thin film such as MnBi or MnCuBi, an amorphous thin film such as GdCo, GdFe, TbFe, DyFe, GdTbFe, TbDyFe, GdFeCo, TbFeCo or GdTbCo, or a single crystal thin film such as GdlG.
Of these thin films, the amorphous thin film is recently considered excellent as the recording layer of the opto-magnetic recording medium with the film formability with which a thin film of large area is made at a temperature in the vicinity of room, temperature, the writing-in efficiency for writing signals at small opto-thermal energy and the readingout efficiency for reading out the written signals at a good S/N ratio being taken into account.
Particularly, GdTbFe, which has a great Kerr rotation angle and a curie point of about 150.
degree.
C.
, is best suited as the material for the opto-magnetic medium.
However, amorphous magnetic materials including GdTbFe have a disadvantage that they are generally inferior in corrosion resistance and tend to be corroded in an atmosphere having moisture and their magnetic characteristic is deteriorated.
If an element such as Si, Cr or Ti is added to the amorphous magnetic material to overcome such disadvantage, the corrosion resistance will be improved, but instead there will occur a disadvantage that the curie point is elevated and the recording sensitivity is reduced.
To eliminate such disadvantage, there have heretofore been proposed disk-like opto-magnetic recording mediums of the type in which various protective layers are provided on a recording magnetic layer of amorphous magnetic material, or of the air sandwich structure in which the recording magnetic layer is enveloped by inert gas, or of the cemented structure in which a substrate is further provided on the recording magnetic layer with an adhesive agent interposed therebetween