GLOBAL RANDOM-FIELD SPIN-GLASS PHASE-DIAGRAMS IN 2 AND 3 DIMENSIONS

An Ising model including field randomness and +/-J bond randomness is studied by renormalization-group theory in spatial dimensions d=2 and 3. In d=3, with field randomness but no +/-J randomness, ferromagnetic and paramagnetic phases occur with no intervening spin-glass phase. A lso in d=3, at sufficient +/-J randomness, a spin-glass phase occurs, but is replaced by the paramagnetic phase for any nonzero random field , also implying its disappearance for any nonzero uniform field. In d= 2, no ferromagnetic phase under random fields and no spin-glass phase occur. Global phase diagrams uniting the random-field and spin-glass p roblems are evaluated. The strong violation of critical phenomena univ ersality, previously found adjoining random-bond tricriticality in d=3 , is seen here in d=2.