Novel Magneto-Optical Media with Direct Overwritability by Exchange-Coupled Quadrilayer Film

A direct overwrite method by light intensity modulation using only an external magnet is described. The recording medium consists of an exchange-coupled RE-TM alloy quadrilayer film. Good recording characteristics were obtained, including a C/N ratio of better than 47 dB at a bit length of 0.76 ¿m without a residual signal. The process in which the second layer is initialized is particularly important. M-H loop measurements revealed that the second layer has two different coercivities with respect to the magnetization states of the other layers; the coercivity of the second layer is smaller than that of a single layer of the same material when the sublattice magnetization of the first layer is antiparallel to the fourth layer magnetization. These phenomena aid in the initialization of the second layer.