Method for magnetic recording on patterned multilevel perpendicular media using thermal assistance and fixed write current
View Patent ↗A method for magnetic recording uses a fixed write current with thermal assistance to record on a patterned perpendicular magnetic recording medium. The patterned medium has magnetic blocks or islands, each of which contains a stack of individual magnetic cells to provide multilevel recording. Each cell in an island is formed of a material or set of materials to provide the cell with perpendicular magnetic anisotropy and is a single magnetic domain. Each cell is magnetically decoupled from the other cells in its island by nonmagnetic spacer layers. Thus each cell can have a magnetization (magnetic moment) in one of two directions (into or out of the plane of the layer making up the cell), and this magnetization is independent of the magnetization of the other cells in its island. This permits multiple magnetic levels or states to be recorded in each magnetic island.
1. A method for recording multiple magnetic levels on a magnetic recording medium comprising:
providing a magnetic recording medium having a substrate and a plurality of spaced-apart magnetic islands arranged on the substrate, each island comprising at least two stacked magnetic cells and a nonmagnetic spacer layer between said at least two cells, each cell in an island being a single magnetic domain having a magnetic moment oriented in one of two opposite directions substantially perpendicular to the substrate, the cell closest to the substrate in each of the islands having a coercivity greater than the other cells in the islands;
applying to an island a magnetic field greater than the coercivity of the cell farthest from the substrate to switch the orientation of the magnetic moment of said farthest cell in that island without switching the orientation of the magnetic moment of the cell closest to the substrate in that island; and
applying to an island said magnetic field while heating that island to switch the orientations of the magnetic moments of all the cells in that island.
2. The method of claim 1 wherein providing the magnetic recording medium comprises providing a magnetic recording disk having the magnetic islands arranged on the substrate in generally concentric tracks.
3. The method of claim 1 further comprising providing an inductive write head and wherein applying the magnetic field comprises applying a write current in one of two directions to thereby generate said magnetic field in one of two directions.
4. The method of claim 3 wherein the head is a longitudinal inductive write head and wherein applying the magnetic field comprises applying a fringe field oriented generally perpendicularly to the substrate.
5. The method of claim 3 wherein the head is a perpendicular inductive write head and wherein applying the magnetic field comprises applying a field oriented generally perpendicularly to the substrate.
6. The method of claim 1 wherein heating the island comprises providing an electrically resistive heater adjacent the inductive write head and applying electrical current to the heater.