From ferromagnetic-ferromagnetic to ferromagnetic-antiferromagnetic exchange coupling in NiFe/MnNi bilayers

The effect of the growth conditions and the Mn concentration on the exchange coupling between a ferromagnetic (F) NiFe and an antiferromagnetic (AF) MnNi layers were studied. We found that an F/AF coupling appears in the bilayers when the Mn concentration is more than 45%. Beyond this critical concentration the exchange field shows a maximum then decreases. The correlation between the exchange field and the microstructure of the film is discussed. We show that: (1) the enhancement of the exchange field is associated with the enhancement of the antiferromagnetic grain size and (2) the existence of the exchange field is associated with a third x-ray peak which may be an FeMnNi ternary allow type. This result was associated with interfacial diffusion confirmed by magnetization variation measurements before and after annealing. (C) 2001 American Institute of Physics.