On the basis of a numerical study of a mean-field free-energy surface, the authors propose that an isotropic Heisenberg spin-glass has no irreversibility. The field-cooled and zero-field-cooled states are the same and magnetic hysteresis is absent. The authors show how Dzyaloshinsky-Moriya and uniaxial anisotropy effects lead to irreversibility. Hysteresis loops exhibit sharp jumps at constant field only when both microscopic anisotropy and a ferromagnetic tendency are present.

• Received 27 September 1982

DOI:https://doi.org/10.1103/PhysRevLett.50.80