Effect of the decomposition process in the magnetic properties of disordered FePd alloys

The influence of the decomposition process from disordered to ordered phase s on the magnetic properties of several FePd-based alloys (Fe75Pd25 and Fe2 1Pd79) has been investigated by X-ray diffraction and VSM magnetometry. The starting material mainly consist of the non-equilibrium disordered FePd ph ases (BCC for Fe75Pd25 and FCC for Fe21Pd79), which upon thermal treatments evolve to their respective equilibrium phase distributions; namely, the co existence of alpha-Fe and gamma(1)-FePd ordered phases in Fe75Pd25, and the precipitation of the gamma(2)-FePd3 ordered phase in the Fe21Pd79 sample. In the Fe-rich sample, the precipitation of the ordered gamma(1)-FePd equil ibrium phase leads to a magnetic hardening with respect to the initial diso rdered state. The Fe21Pd79 presents an order-disorder transition that deter mines the evolution of the magnetic behavior of the sample. By annealing, g amma(2)-FePd3 and disordered gamma-FePd regions coexist. The increase in th e volume fraction of the ordered gamma(2)-FePd3 phase with the thermal trea tments, plays the dominant role in the evolution of the magnetic properties of the sample. (C) 1999 Elsevier Science B.V. All rights reserved.