MAGNETIC-ORDERING TRANSITIONS IN BETA-DYH2-HOH2+X(X AND BETA)

Low-field a.c. magnetic susceptibilities X were measured at low temper ature (1.8 - 30 K) in beta-phase dysprosium and holmium dihydrides, Dy H2+x (0 less-than-or-equal-to x less-than-or-equal-to 0.23) and HoH2+x (0 less-than-or-equal-to x less-than-or-equal-to 0.19). Both systems exhibit breaks or broad maxima at T(M) for all concentrations, indicat ing the onset of magnetic ordering. In DyH2+x, T(M) decreases first fo r small x-values, then increases for higher x: from T(M) almost-equal- to 5 K, for x = 0, up to approximately 15 K, for x = 0.23; in the case of x = 0, an additional inflexion point is observed at T(N) almost-eq ual-to 3.5 K. In HoH2+x, the maximum lies between 5.9 and 7.2 K and, f urthermore, a small step is obtained at 3.5 K for x = 0. In both syste ms, the variation of X in the ordered T-range becomes progressively fl atter with increasing x. The results are compared with recent neutron- diffraction and electrical-resistivity measurements and discussed in t he framework of various AF phase transitions interacting with eventual structural long-range order in the x-sublattice via the crystal field .