The Role of the Nature of Magnetic Coupling on the Martensitic Transformation in Fe-Ni

Fe,,,Ni, with xs30 at.%, known as anti-Invar alloys, undergo mprtensitic transformations. Total energy calculations have shown that these alloys incorporate a strongly fluctuating magnetic moment in the fcc state. In order to undeixtand the relationship between the moment fluctuations and the martensitic transformation, we have investigated the magnetic moment in the paramagnetic fcc state of these alloys by polarized neutron diiaction. We find that the magnetic torrelatiom are ferromagnetic in nature although, the ground state of these alloys are expected to be antiferromagnetic. We fuaher obseme that the magnetic moment of the fcc state at M, increases with increasing Ni concentration, indicating that the fcc state is stabilized by increasing ferromagnetic exchange. The results are found to be in agreement with thermodynamical predictions.