  A modified effective field model was developed to quantitatively interpret
the angular dependent magnetization reversal processes in exchange biased
Fe/IrMn bilayers. Several kinds of multi-step loops with distinct magnetization
reversal routes were observed for the samples measured at various field
orientations. Two types of angular dependent switching fields are observed and
their transitions are investigated, which are found to be driven by both Fe and
IrMn layer thicknesses. Our modified effective field model can nicely describe
all the switching field behaviors including the critical effects of the
exchange bias induced uniaxial anisotropy on the magnetization reversal
processes.
