  The generic problem of extracting information on intrinsic particle
properties from the whole class of interacting magnetic fine particle systems
is a long standing and difficult inverse problem. As an example, the Switching
Field Distribution (SFD) is an important quantity in the characterization of
magnetic systems, and its determination in many technological applications,
such as recording media, is especially challenging. Techniques such as the
first order reversal curve (FORC) methods, were developed to extract the SFD
from macroscopic measurements. However, all methods rely on separating the
contributions to the measurements of the intrinsic SFD and the extrinsic
effects of magnetostatic and exchange interactions. We investigate the
underlying physics of the FORC method by applying it to the output predictions
of a kinetic Monte-Carlo model with known input parameters. We show that the
FORC method is valid only in cases of weak spatial correlation of the
magnetization and suggest a more general approach.
