Magnetic properties of Fe0.9-qMn0.1Alq disordered alloys: Theory

Abstract

ABSTRACT: By using the free-energy variational method based on the Bogoliubov inequality and a diluted and randombond Ising model with nearest-neighbors interactions, we investigate the magnetic phase diagram and some of the magnetic properties of the disordered Fe0.92qMn0.1Alq alloys system. Thus the mean magnetization per site, and hence the average hyperfine magnetic field, are computed. The so-obtained results are compared with room-temperature experimental data obtained by 57Fe Mo¨ssbauer spectroscopy and vibrating sample magnetometry, from which a very good agreement is achieved. Here, the occurrence of a ‘‘critical concentration’’ at 40.0 at.% Al, for which the system passes from a ferromagnetically ordered state to a paramagnetic one, is evidenced. The model allows obtaining an estimate of the exchange energy between Fe-Fe pairs. How this energy depends on the Al concentration and the role of the manganese atoms is also presented and discussed.