Eur. Phys. J. B 27, 347-354 (2002)
https://doi.org/10.1140/epjb/e2002-00165-2

Effective hyperfine temperature in frustrated Gd₂Sn₂O₇: two level model and ¹⁵⁵Gd Mössbauer measurements

¹ Commissariat à l'Énergie Atomique, Service de Physique de l'État Condensé, 91191 Gif-sur-Yvette, France
² Commissariat à l'Énergie Atomique, Service de Physique Statistique, Magnétisme et Supraconductivité, 38054 Grenoble, France

Corresponding author: ^a bonville@spec.saclay.cea.fr

Received: 17 October 2001
Published online: 6 June 2002

Abstract

Using ¹⁵⁵Gd Mössbauer spectroscopy down to 27 mK, we show that, in the geometrically frustrated pyrochlore Gd₂Sn₂O₇, the Gd³⁺ hyperfine levels are populated out of equilibrium. From this, we deduce that the hyperfine field, and the correlated Gd³⁺ moments which produce this field, continue to fluctuate as . With a model of a spin 1/2 system experiencing a magnetic field which reverses randomly in time, we obtain an analytical expression for the steady state probability distribution of the level populations. This distribution is a simple function of the ratio of the nuclear spin relaxation time to the average electronic spin-flip time. In Gd₂Sn₂O₇, we find the two time scales are of the same order of magnitude. We discuss the mechanism giving rise to the nuclear spin relaxation and the influence of the electronic spin fluctuations on the hyperfine specific heat. The corresponding low temperature measurements in Gd₂Ti₂O₇ are presented and discussed.