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

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 3.7x1015/cm2 prior to the annealing increases the exchange field by 21% without altering the blocking temperature (>400 deg. 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