FERROMAGNETISM IN AN INTERMETALLIC COMPOUND CONTAINING PALLADIUM, TITANIUM AND ALUMINUM

Ferromagnetism has been observed in a ternary intermetallic compound whose constituent elements themselves do not order magnetically. The compound formed at the stoichiometric composition Pd2TiAl has the cubic Heusler L2(1) structure and a lattice parameter of 6.322 Angstrom. Magnetisation measurements made between 2 and 300 K and in applied fields of up to 5 T indicated a ferromagnetically ordered state. On the basis of these measurements, the saturation magnetic moment per Pd2TiAl formula unit was determined to be (0.21 +/- 0.005)mu(B). Furthermore, the spontaneous magnetisation only decreases by approximately 3% between 2 and 300 K. If a Brillouin variation of the magnetisation is assumed, then a Curie temperature must be at least 900 K. The observed decrease in the magnetisation follows very closely a T-2 dependence expected for Stoner behaviour. However, since the spontaneous moment is roughly half that of nickel and the Curie temperature is nearly that of iron, the compound does not fall into the category of a weak itinerant ferromagnet. A model based on a band structure description is put forward to account for the observations.