Two-bit-per-dot patterned media combining in-plane and perpendicular-to-plane magnetized thin films

We demonstrate the possibility of doubling the areal density of information in magnetic patterned media by stacking decoupled in-plane and perpendicular-to-plane magnetized layers. Each dot can be set in four magnetostatically equivalent configurations, yielding a storage capability of two-bits per dot. Magnetic force microscopy analyses show that the magnetic signal from the out-of-plane magnetized layer is dominant right above the dots, whereas, the signal from the in-plane magnetized layers is largest above the spacing between dots. This results in an optimal use of the storage space and in an increase of the areal density with weak loss in readout signal-to-noise ratio.