Influence of phase transformation on the permanent-magnetic properties of Fe-Pt based alloys

We have studied the effect of the atomic disorder-order transformation on r emanence enhancement and coercivity in Fe-Pt-based materials by isothermal annealing at temperatures well below the transformation point. We also inve stigated the effect of the annealing temperature and the effect of various types of additives. The relative amount of the low-temperature hard-magneti c face-centered-tetragonal (FCT) phase precipitated in the high-temperature magnetically soft face-centered-cubic (FCC) phase was determined by means of X-ray diffraction. As a function of annealing time and annealing tempera ture, particle size and relative amount of the FCT phase increased at the c ost of the FCC phase. These changes were followed by means of magnetic meas urements. We observed a continuous increase in coercivity with increasing a nnealing time, eventually reaching a maximum. The Kneller-Hawig model was u sed to explain the occurrence of remanence enhancement and the continuously changing degree of exchange coupling between the magnetically soft and har d phase. The suitability of Fe-Pt based alloys in dental applications is di scussed. (C) 2001 Elsevier Science B.V. All rights reserved.