Structure and magnetism in Pr3RuO7

The crystal structure of the ordered fluorite, Pr3RuO7, was refined from powder neutron diffraction data in Cmcm. An interesting structural feature is the presence of relatively well separated zig-zag chains of corner sharing RuO6 octahedra, Ru-Ru interchain distance 0.61 Angstrom vs. Ru-Ru intrachain distance of 3.76 Angstrom. Magnetic susceptibility data show a Curie-Weiss behavior for T>225 K with C=5.96(4) emu K mol(-1) and theta(c)=+11(2) K. In an attempt to separate the contributions of Pr(3+) and Ru(5+), the properties of isostructural Pr3TaO7 were also measured, yielding C=4.63(3) emu K mol(-1). Thus, the contribution of Ru(5+), 4d(3), S=3/2, to the measured Curie constant is estimated to he 1.33 emu K mol(-1), not far from the spin-only value of 1.87 emu K mol(-1). This supports the view that the Ru 4d elections are localized acid magnetic, not itinerant. A susceptibility maximum at about 50 K is attributed to long-range magnetic order and this is substantiated by neutron diffraction data. There is little evidence for one-dimensional antiferromagnetic correlations in this material but behavior characteristic of short-range ferromagnetic correlations attributed to Pr-Ru exchange interactions are found in the temperature range 50-200 K, consistent with the positive theta(c). (C) 2000 Elsevier Science Ltd. All rights reserved.