Patent ID: 6882488

Claim:
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 a first magnetic field to an island to switch the orientation of the magnetic moment of at least one cell in the island without switching the orientation of the magnetic moment of the cell closest to the substrate; and applying a second magnetic field having a strength greater than said first field to an island to switch the orientations of the magnetic moments of all the cells in the island.