Spin frustration and antiferromagnetic long range order in R2BaPdO5 (R=rare earth)

Antiferromagnetic ordering and spin frustration behaviors in the series of isostructural compounds, R2BaPdO5 (R=rare earth), are reported. We have investigated the crystallographic, magnetic and thermal properties of the compounds, R2BaPdO5 (R=Nd, Eu, Gd and Ho). R2BaPdO5 (R=Nd, Gd and Ho) show paramagnetic properties at high temperatures originating only from the rare-earth ions and magnetic order at 2.1, 2.9 and 4.1 K, respectively. Ho2BaPdO5 shows a symmetrical peak of the heat capacity at TN and negligible residual entropy below the TN, suggesting a simple square lattice Ising model. On the contrary, Nd2BaPdO5 and Gd2BaPdO5 show Schottky type heat capacity at TN and large residual entropy far below the TN, suggesting spin frustration in them. The origin of the possible spin frustration in R2BaPdO5 (R=Nd and Gd) is discussed in terms of relative strength of J and J' in the Shastry-Sutherland spin lattice