ABSTRACT
The capacity of hard disk drives (HDDs) is determined by the phys-
ical size of an information bit. In conventional HDDs an individual
bit consists of about 10 to 15 weakly magnetically coupled CoCrPt
grains [1]. To further increase the areal storage density (number
of bits per unit area), a reduction of the dimensions of the grains
is required. However, this reduction has a lower boundary, as with
reduction of the grain size, the magnetic anisotropy energy Keff · V (Keff being the effective magnetic anisotropy constant and V being the volume of a grain) will come closer to the thermal activation
energy. Thus, the recording medium reaches the superparamagnetic
limit and becomes thermally instable [1-4].
