Field-cooling induced unidirectional anisotropy in the two-dimensional Ising antiferromagnet Rb2Cu1−xCoxF4

Abstract Small cluster approximation and Monte Carlo Metropolis algorithm are applied to demonstrate that field cooling induces a unidirectional magnetic anisotropy of small clusters of Cu in Rb2Cu1−xCoxF4. Within the Ising model, this anisotropy appears as a net magnetization at zero magnetic field. The effect is due to a coupling between the orbital ordering within clusters of Cu impurities and the antiferromagnetic ordering of Co matrix.