  Multiphase magnetic systems are common in nature and are increasingly being
recognized in technical applications. One characterization method which has
shown great promise for determining separate and collective effects of
multiphase magnetic systems is first order reversal curves (FORCs). Several
examples are given of FORC patterns which provide distinguishing evidence of
multiple phases. In parallel, a visualization method for understanding
multiphase magnetic interaction is given, which allocates Preisach magnetic
elements as an input 'Preisach hysteron distribution pattern' (PHDP) to enable
simulation of different 'wasp-waisted' magnetic behaviors. These simulated
systems allow reproduction of different major hysteresis loop, FORC pattern,
and switching field distributions of real systems and parameterized theoretical
systems. The experimental FORC measurements and FORC diagrams of four
commercially obtained magnetic materials, particularly those sold as
nanopowders, shows that these materials are often not phase pure. They exhibit
complex hysteresis behaviors that are not predictable based on relative phase
fraction obtained by characterization methods such as diffraction. These
multiphase materials, consisting of various fractions of BaFe12O19,
epsilon-Fe2O3, and gamma-Fe2O3, are discussed.
