Bragg-Williams model of Fe-Co order-disorder phase transformations in a strong magnetic field

摘要

A modified Bragg-Williams statistical model with nearest-neighbor magnetic exchange and chemical interactions and an additional Zeeman energy term has been used to predict an increase in the critical ordering temperature (T_(order)) of Fe-Co alloys in the presence of a large magnetic field ( DELTA T_(order) approx 20 K near equiatomic composition for H=100 T). The magnitude of the predicted DELTA T_(order) increases with increasing field and is only predicted to be significant (DELTA T_(order) > = 2-3 K near equiatomic) for H > = 10 T. The predicted shift in the ordering temperature is due to the higher average exchange interaction per atom in the ordered phase resulting in a larger theoretical Curie temperature as compared to the disordered phase. The dependence of the average magnetic moment of Fe on the degree of order was neglected in this work, however it is expected to contribute to an additional shift in T_(order). Theoretical magnetization versus temperature curves are also presented for equiatomic FeCo subject to uniform applied magnetic fields.