MAGNETIC CHARACTERISTICS OF EUROPIUM-ALUMINUM INTERMETALLICS

Bulk magnetic characteristics of EuAl4 and EuAl4 are reported for temperatures ranging from 4°-300°K and for field strengths up to 20 kOe. To evaluate the influence of electron concentration on the magnetic interactions a series of EuxLa1-xAl2 alloys, with x ranging from 0.1 to 0.8, was studied over the same interval of temperature and field strength. Between 50° and 300°K all samples exhibited Curie-Weiss behavior with an effective moment characteristic of dipositive europium. EuAl4, EuAl2, and Eu 0.8La0.2Al2 become antiferromagnetic below 20°K, two types of antiferromagnetic order being indicated for the latter two intermetallics. Increasing the electron concentration by replacing Eu with tripositive La alters the interaction from predominantly antiferromagnetic to predominantly ferromagnetic as the electron concentration approaches 9. The change in sign of the interaction occurs at about 8.4 electrons per magnetic atom. Eu0.1La0.9Al2 and Eu0.2La 0.8Al2 are ferromagnetic at 4°K with Eu moments of about 5 μa per formula unit. Eigenvalues of the spin-Hamiltonian are obtained for Eu++ in a site of tetragonal symmetry and used to interpret the saturation moments observed for the ferromagnetic ternaries and the deviations from CurieWeiss behavior for EuAl2 and the (Eu, La) Al2 alloys. The bulk magnetic properties can be quite successfully accounted for on the basis of an over-all (Zeeman-like) splitting of 480°K.