Structure and magnetism in Pr RuO 3 7 *

The crystal structure of the ordered fluorite, Pr RuO , was refined from powder neutron diffraction data in Cmcm. An interesting 3 7 structural feature is the presence of relatively well separated zig-zag chains of corner sharing RuO octahedra, Ru–Ru interchain distance 6 ̊ ̊ 6.61 A vs. Ru–Ru intrachain distance of 3.76 A. Magnetic susceptibility data show a Curie–Weiss behavior for T.225 K with 21 C55.96(4) emu K mol and u 5111(2) K. In an attempt to separate the contributions of Pr(31) and Ru(51), the properties of c 21 3 isostructural Pr TaO were also measured, yielding C54.63(3) emu K mol . Thus, the contribution of Ru(51), 4d , S53/2, to the 3 7 21 21 measured Curie constant is estimated to be 1.33 emu K mol , not far from the spin-only value of 1.87 emu K mol . This supports the view that the Ru 4d electrons are localized and 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 u .  2000 Elsevier Science Ltd. All rights reserved. c