Phase diagrams of weakly anisotropic Heisenberg antiferromagnets: III. Nonlinear excitations and random fields in quasi 2-dimensional systems

Abstract

The concept of effective field-dependent anisotropy is applied to the “spinflop” transition in the quasi 2-d Heisenberg antiferromagnet with weak orthorhombic anisotropy. From the correspondence between the “spinflop” problem and the commensurate-incommensurate transtion it follows that the “spinflop” is not first order and that random fields may cause domain-wall formation. This would explain the observed broadening of the “spinflop” in K 2MnF 4. In 3-d antiferromagnets such anomalous broadening is not observed, which would agree with the critical dimensionality d c = 2 for the random-field problem.