STRUCTURAL ORIGIN OF MAGNETIC BIASED FIELD IN NIMN NIFE EXCHANGE-COUPLED FILMS/

The factors which determine the strength of the magnetic biased field in NiMn/NiFe exchange biased system have been examined. It was found t hat a strong NiFe (111) texture and columnar growth are essential to o btaining a high exchange field as they facilitate epitaxy between the NiFe and NiMn layers. The application of an amorphous Ta nucleation la yer and substrate biasing during NiFe deposition have been found to pr omote these structures. Fee NiMn replicates the (111) texture through epitaxial growth on NiFe according to a cube on cube orientation relat ionship. Upon annealing, atomic ordering takes place in the NiMn layer and gives rise to an exchange biased field. However, a fully L1(0) or dered structure cannot be achieved at the NiMn/NiFe interface due to t he stabilizing effect of fee NiFe. Away from the interface, the transf ormation proceeds and the ordered tetragonal unit cell creates a latti ce strain within the NiMn film. This strain is relieved by twinning wi thin the NiMn grains of the film. The strength of the exchange field h as been found to be closely associated with the density of twins and t heir proximity to the NiMn/NiFe interface. (C) 1996 American Institute of Physics.