Three-dimensional magnetic interactions in quasi-two-dimensional PdAs₂O₆

Millimeter-sized PdAs₂O₆ single crystals are grown using the vapor transport technique. The magnetic order at K is studied by measuring magnetic properties, specific heat, and neutron single crystal diffraction. The anisotropic magnetic susceptibility and a metamagnetic transition observed in magnetic fields above 20 kOe suggest that the magnetic moment lies in the ab plane, consistent with the magnetic structure determined by neutron single crystal diffraction. Below 140 K, Pd²⁺ ions order ferromagnetically in the ab plane but antiferromagnetically along the crystallographic c axis. The ordered moment is refined to be 2.09(2) /Pd²⁺ using the fitted magnetic form factor of Pd²⁺. A weak λ-type anomaly around T _N was observed in specific heat and the magnetic entropy change across T _N is 1.72 J mol^-1 K.This small entropy change and the temperature dependence of the magnetic susceptibility support the presence of short range correlations in a wide temperature range 250 K. The comparison with SrRu₂O₆ suggests that the magnetic interactions in PdAs₂O₆ are dominated by Pd-(O - O)-Pd super-superexchange and three dimensional despite the quasi-two-dimensional arrangement of magnetic ions. The comparison with NiAs₂O₆ suggests that increasing covalency of isostructural compounds is an effective approach to design and to discover new materials with higher magnetic order temperatures in the localized regime.