Many of the theoretical aspects the recording physics of
BPMR are well developed and have an extensive record in the
literature [9], [10], [11], [12]. If the island has a single magnetic
layer, each island switches quasi-uniformly and is generally
well-described by Stoner-Wohlfarth theory [13]. In exchange
spring media [14], [15], two or more materials are combined to
render the islands writeable while maintaining thermal stability
at sufficiently small island volume for the desired areal bit
density. Yet even in the case of exchange spring media the
underlying recording physics of BPMR media is relatively
simple, since there are no complications from the traditional
granular media noise, grain size distributions, etc., of
unpatterned media. Challenges for BPMR designs become
evident, however, when the media design questions are linked
to BPM fabrication capabilities, where limitations in
lithography, imprint technology, etch processes, etc. emerge as
major constraints