MAGNETIC AND CRYSTALLOGRAPHIC CHARACTERISTICS OF (PRLA)AL3 (PRY)AL3 (PRLA)AL2 AND (PRY)AL2

Magnetization data are reported for PrAl2 (cubic) and PrAl3 (hexagonal) and ternary alloys in which Pr is partially replaced by Y and La. Between 50 and 300°K Curie-Weiss behavior is observed with slopes as expected for tripositive Pr. The cubic alloys exhibit Curie temperatures ranging from 38.5°K for PrAl2 to 5°K for Pr0.05La0.95Al2. Pr0.95Y0.95Al2 is the single exception; it remains paramagnetic to 4°K. The hexagonal alloys all develop Van Vleck paramagnetism at low temperatures. The operator equivalent method is employed to obtain eigenfunetions, eigenvalues and magnetic moments for the crystal field states for Pr+3 in both the cubic and hexagonal environments. Fourth and sixth order interactions are included in both instances and the second order term is also included for PrAl3 since its axial ratio is not ideal. Susceptibility-temperature behavior of PrAl3 and the hexagonal ternaries can be accounted for with two sets of parameters which concern the relative importance of the second, fourth and sixth order interactions; in each case the overall splitting is about 120°K. The maximal value of the overall splitting for the cubic alloys is established to be 25°K. Using a molecular field approach it is possible to understand the development of ferromagnetism in PrAl2 which occurs despite the lack of a permanent moment for Pr in its ground state. With this approach Tc is calculated to be 39°K, which is in excellent agreement with experiment, 38.5°K. The same approach gives a reasonably satisfactory accounting for the composition dependence of Tc and the saturation moment. © 1969.