Phase diagram of a highly diluted, disordered Ising system: The Al-rich, Al-Fe system

Disordered solid solutions containing a highly diluted magnetic element in which competitive exchange interactions are present can allow the observati on of magnetic ordering (ferromagnetism, antiferromagnetism, and spin-glass behavior) at dilutor element contents different from those corresponding t o ordered alloys. In this work we present a simulational study of the magne tic properties of the Al-rich, Al-Fe disordered alloy system, which meets t he above mentioned requirements and is therefore a good candidate to show d ifferences between the magnetic phase diagrams corresponding to the ordered and disordered states. Our simulations were carried out on the basis of a randomly site-diluted Ising model, using the Monte Carlo method as energy m inimization tool. In our model, the spins of the Fe atoms are assumed to be coupled by a direct nearest-neighbor ferromagnetic exchange J (depending o n the Al concentration), and by an ill-mediated antiferromagnetic superexch ange interaction - alpha J. Our results suggest the presence of ferromagnet ic order for Al concentrations higher than those for which that order disap pears in ordered alloys and the occurrence, for Fe atomic percentages betwe en 10% and 25%, of a re-entrant spin glass phase whose freezing temperature decreases with the degree of dilution. (C) 1998 American Institute of Phys ics. [S0021-8979(98)34211-5].