Self biasing thermal magneto-optic medium

DETAILED DESCRIPTION A magnetic field biasing layer for a storage device has temperature dependent magnetic properties.
The layer has a net magnetization which changes in orientation as a function of temperature.
It comprises two oppositely oriented magnetic material components.
One material having this kind of magnetic property is known as a ferrimagnetic material.
As the temperature of the biasing layer rises, the magnetization of both component materials decreases, but the rate of decrease is different.
The net magnetization is the difference between the two component materials.
At the compensation temperature, the magnetization of both materials are equal.
Since they are oppositely directed, the net magnetization is zero.
As the temperature increases past the compensation temperature, the orientation of the net magnetization changes direction because of the different rate of change of magnetization of the two component materials.
Because of the change in direction of magnetization as a function of temperature, this layer can be used to bias a magnetic storage device to provide desired magnetic field orientations.
In one preferred embodiment, a self biasing magneto-optic storage medium has a first magnetic layer which retains desired magnetic field orientations representative of data in discrete domains of magnetization.
A second magnetic layer as described above is coupled to the first magnetic layer and provides a biasing field for obtaining the desired magnetic field orientations in the first magnetic layer.
To record data in the storage medium, a portion of the first layer corresponding to a magnetic domain is heated from ambient temperature as by a laser to a temperature at or above its Curie temperature.
The second layer is a ferrimagnetic biasing layer having a compensation temperature, and is heated by the same laser coincidental to the heating of the first layer.
Prior to the heating of the layers, the direction of magnetizations of the domains in both layers is the same, for example, up