COMPETITION BETWEEN AXIAL AND CUBIC ANISOTROPIES IN HEISENBERG SPIN-GLASSES

An infinite-range quantum Heisenberg spin glass with uniaxial (D) and cubic (K) anisotropies is studied using the thermo-held-dynamic method . Mean-field theory phase diagrams in the temperature-anisotropy plane (T,D) for quantum spins S = 2 and S = 5/2 are presented for different values of K. Generally, for integer spin values and large anisotropy D a condensation into a nonmagnetic spin state occurs, accompanied by the destruction of the spin-glass order as indicated by the finite cri tical value D-c(T=0). For half-integer S and sufficiently low temperat ure, the spin-glass phase persists for arbitrary D and K. In both case s the presence of a cubic term induces complicated crossovers from lon gitudinal to transverse freezing of spins.