MAGNETIC 1ST-ORDER PHASE-TRANSITION AND CROSSOVER ASSOCIATED WITH RANDOM ANISOTROPY IN CRYSTALLINE DYXY1-XAL2

The low-temperature (T = 0 K) first-order phase transition, predicted to drive systems with both weak random and uniform cubic anisotropy from a correlated spin glass to a ferromagnet, has been observed. At higher temperatures the transition is to a quasi- or random ferromagnet. The transition occurs at a concentration x(t) = 0. 62 +/- 0.01 in the crystalline Laves-phase compounds DyxY1-xAl2. At concentrations above x(t), a line of transition is observed between the paramagnetic and random ferromagnetic phases, as found previously. This line is characterized by the crossover exponent phi(DELTA) = 0.80 +/- 0.08, in good agreement with prediction. Two multicritical points have been identified at x(t) = 0. 62 +/- 0.01, T(t) = 29.5 +/- 0.1 K and at around x(t)' = 0. 87, T(t)' = 45.4 K.