99Ru Mossbauer effect Measurement in Pr3RuO7 and Gd2RuO5

99Ru Mossbauer measurements have been made in polycrystalline samples of Pr3RuO7 and Gd2RuO5 at 4.2K. Pr3RuO7 is a magnetic insulator with strong d-f electron coupling and multiple magnetic phase transitions. The Mossbauer spectrum of Pr3RuO7 shows that: (1) Ru has an isomer shift, which is consistent with a charge state of +5, (2) a hyperfine magnetic field of about 60T (3) a small electric quadrupole interaction. The charge state of Ru and hyperfine magnetic field is consistent with other antiferromagnets (Na3RuO4, GdRuSr2Cu2O8, Sr2YRuCuO6). The small electric field gradient shows the non-cubic environment for Ru within RuO6. Gd2RuO5 is also a magnetic insulator with a large specific heat. 1 The 99Ru Mossbauer spectrum of Gd2RuO5 shows a broadened single line centered at -0.34mm/s that is consistent with a +4 state for Ru. Gd2RuO5 is magnetic below 9K, as shown by magnetization measurements. 1 The hyperfine magnetic field which can be fit to this single line is small, <10T, and such a small hyperfine magnetic field is unusual in the magnetic ruthenate compounds. 1. G.Cao, S. Mc Call, Z.X. Zhou, C. S. Alexander, J.E. Crow, Phys. Rev B, 63, 144427(2001)