Neutron depolarization study of the magnetic phase transition in a disordered system

The ferromagnetic phase transition in the invar alloy Fe70Ni30 (0.7 at% C) with fully FCC structure was investigated by means of 3-D neutron depolariz ation analysis. The mean magnetic induction,magnetic anisotropy parameter a nd neutron depolarization were measured as a function of temperature and ex ternal magnetic held. Our experiments show the appearance of large magnetic inhomogeneities with size about 10(3)-10(4) Angstrom in the paramagnetic t emperature range. The data were interpreted using the concept of a probabil ity function rho(T-c) which describes the variations of the Curie temperatu res over the system. (C) 1999 Elsevier Science B.V. All rights reserved.