Eur. Phys. J. B 33, 173-181 (2003)
https://doi.org/10.1140/epjb/e2003-00154-y

Magnetic properties of Yb₂Mo₂O₇ and Gd₂Mo₂O₇ from rare earth Mössbauer measurements

¹ Commissariat à l'Énergie Atomique, Centre d'Études de Saclay, Service de Physique de l'État Condensé, 91191 Gif-sur-Yvette, France
² Commissariat à l'Énergie Atomique, Centre d'Études de Grenoble, Service de Physique Statistique, Supraconductivité et Magnétisme, 38054 Grenoble, France
³ Institute of Physics, Jagiellonian University, 30-059 Kraków, Poland

Corresponding author: ^a hodges@drecam.saclay.cea.fr

Received: 13 January 2003
Published online: 4 June 2003

Abstract

Using ¹⁷⁰Yb and ¹⁵⁵Gd Mössbauer measurements down to ~ 0.03 K, we have examined the semiconducting pyrochlore Yb₂Mo₂O₇ where the Mo intra-sublattice interaction is anti-ferromagnetic and the metallic pyrochlore Gd₂Mo₂O₇ where this interaction is ferromagnetic. Additional information was obtained from susceptibility, magnetisation and ¹⁷²Yb perturbed angular correlation measurements. The microscopic measurements evidence lattice disorder which is important in Yb₂Mo₂O₇ and modest in Gd₂Mo₂O₇. Magnetic irreversibilities occur at 17 K in Yb₂Mo₂O₇ and at 75 K in Gd₂Mo₂O₇ and below these temperatures the rare earths carry magnetic moments which are induced through couplings with the Mo sublattice. In Gd₂Mo₂O₇, we observe the steady state Gd hyperfine populations at 0.027 K are out of thermal equilibrium, indicating that Gd and Mo spin fluctuations persist at very low temperatures. Frustration is thus operative in this essentially isotropic pyrochlore where the dominant Mo intra-sublattice interaction is ferromagnetic.