R-M interactions in R₂BaMO₅ (R=Y or Gd and M=Cu or Zn)

Abstract

R₂BaMO₅ (R = Gd or Y; M = Cu or Zn) oxides have been studied using the specific heat, DC magnetic susceptibility and electron paramagnetic resonsance (EPR). For one member of the series without a magnetic moment at M, namely Gd₂BaZnO₅, measurements reveal long-range antiferromagnetic order at T_N(Gd₂BaZnO₅) = 2.3 ± 0.1 K, much lower than the Curie - Weiss temperature Θ of 15.9 ± 0.3 K. This indicates the existence of competing interactions that introduce a large degree of magnetic frustration in the system. For Y₂BaCuO₅ the Cu - Cu interactions are responsible for the broad maximum in the magnetic contribution to the specific heat centred at 18.5 ± 0.01 K that stretches beyond the instrumental limit of 25 K. The strong Cu - Cu interactions also present in Gd₂BaCuO₅, combined with the Gd - Cu interaction, polarize the Gd sublattice, giving measurable contributions to the specific heat in the same temperature range. In addition, they broaden the Gd EPR line and saturate its integrated intensity. The ordering temperature of Gd ions is raised to T_N(Gd₂BaCuO₅) = 12.0 ± 0.1 K.