Structure and Magnetic Properties of Sr₂NaOsO₆

Sr2NaOsO6, an ordered double perovskite, was obtained by solid-state synthesis. The compound crystallizes in a monoclinic cell [P2(1)/n, a = 5.7043(1) angstrom, b = 5.7828(1) angstrom, c = 8.0816(2) angstrom; beta = 90.01(2)degrees] and develops long-range antiferromagnetic order at approximate to 17 K with strong canting generating a tiny spontaneous moment of 0.06 mu(B)/Os ion. A fit of the high temperature susceptibility data according to a modified Curie-Weiss law revealed a small effective paramagnetic moment of 0.7 mu(B)/Os, which underlines the substantial effect of spin-orbit coupling in 5d oxides. A broad instead of a sharp lambda anomaly in specific heat data suggests frustration and strong magnetic disorder at the osmium lattice