MACROSCOPIC RANDOM MAGNETIC-ANISOTROPY CONSTANT IN CRYSTALLINE DYXY1-XAL2 (X=0.3, 0.4)

Cooling in a weak magnetic field the random magnetic anisotropy (RMA) spin glasses DyY1-xAl2 (x = 0.3, 0.4) induces unidirectional and uniax ial anisotropies, on top of the cubic coherent one. The unidirectional anisotropy constant K(RMA)u has been determined at 3.8 K, amounting a t zero applied field 127 and 255 j/M3 for x = 0.3 and 0.4, respectivel y. The predicted model ratio between KRMA and the uniaxial constant K( RMA)a, i.e., K(RMA)a = 2K(RMA)u, has been confirmed. As by-product the relevant RMA parameter D2/j, where D is the RMA crystal field strengt h and J, the exchange constant has been determined, as well as separat e estimates of D and J.