Planar Hall effect in NiFe/NiMn bilayers

The exchange anisotropy in NiFe/NiMn bilayers was studied by using the planar Hall effect. The sputtered NiFe/NiMn films were patterned into strips of 1 mm in length and 200 mum in width and with six terminals for anisotropy magnetoresistance and planar Hall voltage measurements by a photolithographic process. It is shown that the planar Hall effect is an effective method to characterize the exchange anisotropy in ferromagnetic/antiferromagnetic (AF) systems. It can be used to accurately determine the exchange field and describe the magnetization reversal processes. The effective uniaxial anisotropy field H-K eff, the effective unidirectional anisotropy field H-ud, and AF domain wall energy H-w can be obtained by fitting the experimental results. We found that in the NiFe/NiMn bilayer system, the parameters H-K eff, H-ud, and H-w have the same values in reversible and irreversible measurements, and the domain wall energy in AF layer is larger than interfacial unidirectional anisotropy. (C) 2001 American Institute of Physics.