Effective hyperfine temperature in frustrated Gd2Sn2O7: two level model and 155Gd Mössbauer measurements
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 firstname.lastname@example.org
Published online: 6 June 2002
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.
PACS: 76.80.+y – Mössbauer effect, other γ-ray spectroscopies / 75.50.Ee – Antiferromagnetics / 75.40.Gb – Dynamic properties / 05.40.-a – Fluctuation phenomena, random processes, noise, and Brownian motion
© EDP Sciences, Società Italiana di Fisica, Springer-Verlag, 2002