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

Abstract

Disordered solid solutions containing a highly diluted magnetic element in which competitive exchange interactions are present can allow the observation of magnetic ordering (ferromagnetism, antiferromagnetism, and spin-glass behavior) at dilutor element contents different from those corresponding to ordered alloys. In this work we present a simulational study of the magnetic properties of the Al-rich, Al–Fe disordered alloy system, which meets the above mentioned requirements and is therefore a good candidate to show differences 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 minimization tool. In our model, the spins of the Fe atoms are assumed to be coupled by a direct nearest-neighbor ferromagnetic exchange J (depending on the Al concentration), and by an Al-mediated antiferromagnetic superexchange interaction −αJ. Our results suggest the presence of ferromagnetic order for Al concentrations higher than those for which that order disappears in ordered alloys and the occurrence, for Fe atomic percentages between 10% and 25%, of a re-entrant spin glass phase whose freezing temperature decreases with the degree of dilution.