PHASE-TRANSITIONS IN SPIN SYSTEMS WITH FRUSTRATIONS

This review surveys recent theoretical and experimental work on phase transitions in frustrated spin systems. Various Ising systems with regular and random distribution of frustrated bonds are studied. The systems under consideration are the Heisenberg and planar spin systems on periodic arrays. In triangular antiferromagnets special attention is paid to magnetic transitions of new universality classes and to transitions of the Berezinsky-Kosterlitz-Thouless type with exponentially decaying spin correlations in the low-temperature phase. The critical exponents found for the frustrated systems considerably differ from the standard nonfrustrated systems. Theoretical predictions are compared with experiments. Phase diagrams for two-dimensional systems are found and the possible existence of a multicritical point associated with a domain-wall-induced vortex-antivortex-unbinding transition is shown. Spin structures are described in compounds where additional frustrations occur in the third direction. Successive phase transitions are considered in 3D frustrated systems with weak dipole interaction. Theoretical calculations for such systems are in good agreement with the experimental data. frustration effects, critical phenomena, topological excitations, symmetry. © 1990, Taylor & Francis Group, LLC. All rights reserved.