Two-Bit-Per-Dot Patterned Media for Magnetic Storage

Bit-patterned recording media are made of arrays of physically separated magnetic nanodots, each nanodot carrying one bit of information. We demonstrate that by stacking perpendicular-to-plane and in-plane magnetized thin films within each magnetic dot, it is possible to obtain a 2-bit-per-dot multilevel magnetic recording system without penalty to the readout signal-to-noise ratio. The stray field above the dots was measured and analyzed by electron holography for different magnetic configurations and compared with numerical simulations. The perpendicular-to-plane magnetized layer mainly influences the stray field above the center of the dots, whereas the in-plane magnetized layer determines the stray field above the gap between dots. The areal density of information can thus be doubled with this media by making an optimum use of the whole area of the medium.