Ab initio investigation of the Invar anomaly in ordered fcc Fe-Pt alloys -: art. no. 064510

The magnetovolume anomaly in ordered fcc Fe-Pt Invar alloys is studied by ab inito Korringa-Kohn-Rostoker atomic-sphere approximation technique in the framework of density-functional theory. The paramagnetic state above the magnetic ordering transition temperature is treated using the disordered local moment (DLM) approach. We show that the DLM approach is able to describe and explain the Invar anomaly in ordered Fe-rich Fe-Pt alloys similarly to our previous work for the disordered modification. In particular, our calculations predict the weakening of the Invar anomaly in chemically ordered compositions as compared to the disordered case as well as a decreasing magnetovolume anomaly with increasing Pt concentrations for both ordered and disordered cases in full agreement with experimental observations. The detailed study of the Fe3Pt compound with varying chemical long-range order has revealed a continuously decreasing spontaneous volume magnetostriction with increasing degree of order. This can be understood from the corresponding band structure of random and ordered alloys.