Susceptibility of ErBa₂Cu₃O₆ single crystal: A dipolar antiferromagnet

The susceptibility of an ErBa₂Cu₃O₆ single crystal was measured at 2 K<T<100 K. The low-temperature (T<10 K) data yield g_∥=5.39 and g_⊥=7.45. The shapes of the susceptibility curves are well explained by the dipolar fields, calculated for the Er³⁺ ions in the layered structure of the sample, and by a small contribution of exchange fields. Extending the calculations to the antiferromagnetic state of ErBa₂Cu₃O₆ shows that this material is well described as a two-dimensional dipolar antiferromagnet. The dipolar field calculations are also applied to DyBa ₂Cu₃O₆ and GdBa₂Cu₃O ₆ and are shown to be compatible with the magnetic structure of these materials.