Effects of structure and ion irradiation on the exchange field of NiFe/NiMn

Abstract NiFe/NiMn exchange field was manipulated by an underlayer NiFeCr or by C ion irradiation. Underlayer NiFeCr significantly promoted (1 1 1) texture growth, leading to a higher exchange field. However, the threshold annealing temperature required to reach a large value of exchange field was raised. This can be attributed to well aligned orientations between NiFe and NiMn at the interface, which stabilizes the FCC γ phase of NiMn and increases the nucleation energy. C ion irradiation with the dosage of 3.7×1015/cm2 prior to the annealing increases the exchange field by 21% without altering the blocking temperature (>400°C). The enhancement of the exchange field by irradiation can be related to the increase of defect sites in NiMn or (and) to the new phase NiMn(C) formation having c/a ratio significantly less than NiMn.