Theory of the successive magnetic phase transitions in tetragonal RBa2Cu3O6+xcompounds

Abstract

A theory based on the analysis of a Landau-type free energy is presented to explain the variety of unusual magnetic phase transitions recently observed in tetragonal RBa2Cu3O6+x compounds with R=Y, Nd. The results show that up to three successive transitions can occur that involve antiferromagnetic orderings of the Cu ions. The number of transitions predicted to occur depends on a delicate interplay among weak inter-planar exchange interactions. Oxygen content is expected to be the principal factor in determining this balance of exchange forces.