FERROMAGNETISM IN AN INTERMETALLIC COMPOUND CONTAINING PALLADIUM, TITANIUM AND ALUMINUM

Ferromagnetism has been observed in a ternary intermetallic compound w hose constituent elements themselves do not order magnetically. The co mpound formed at the stoichiometric composition Pd2TiAl has the cubic Heusler L2(1) structure and a lattice parameter of 6.322 Angstrom. Mag netisation measurements made between 2 and 300 K and in applied fields of up to 5 T indicated a ferromagnetically ordered state. On the basi s of these measurements, the saturation magnetic moment per Pd2TiAl fo rmula unit was determined to be (0.21 +/- 0.005)mu(B). Furthermore, th e 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 decrea se in the magnetisation follows very closely a T-2 dependence expected for Stoner behaviour. However, since the spontaneous moment is roughl y 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 fer romagnet. A model based on a band structure description is put forward to account for the observations.