  Lorentz transmission electron microscopy (LTEM) combined with in-situ
magnetizing experiments is a powerful tool for the investigation of the
magnetization of the reversal process at the micron scale. We have implemented
this tool on a conventional transmission electron microscope (TEM) to study the
exchange anisotropy of a polycrystalline Co35Fe65/NiMn bilayer.
Semi-quantitative maps of the magnetic induction were obtained at different
field values by the differential phase contrast (DPC) technique adapted for a
TEM (SIDPC). The hysteresis loop of the bilayer has been calculated from the
relative intensity of magnetic maps. The curve shows the appearance of an
exchange-bias field reveals with two distinct reversal modes of the
magnetization: the first path corresponds to a reversal by wall propagation
when the applied field is parallel to the anisotropy direction whereas the
second is a reversal by coherent rotation of magnetic moments when the field is
applied antiparallel to unidirectional anisotropy direction.
