Asymmetric recovery effect of exchange bias in polycrystalline NiFe/FeMn bilayers

For exchange bias in polycrystalline NiFe/FeMn bilayers, the hysteretic behavior of the angular dependence and the recovery effect has been studied. In particular, the pinning direction (PD) at the ending remanent state of each hysteresis loop is identified. In the hysteretic behavior, in addition to the coercivity, the PD also demonstrates different angular dependence between clockwise and counterclockwise rotations of the external magnetic field. Measurements of the recovery effect consist of two major steps. In the first step, the PD is deviated from the initial one by using its hysteretic effect and training effect. For polycrystalline NiFe/FeMn bilayers, the rotated PD is located at the maximal angle θPD0 of ±22° with respect to the initial ones. As for the second step, an external magnetic field is applied at a specific orientation θH−RE and then switched off at the same orientation. For the negative θPD0, the recovery effect only occurs for 0<θH−RE<180° with the maximal effect at θH−RE=90° and vani...