Eur. Phys. J. B 16, 647-651 (2000)
https://doi.org/10.1007/s100510070181

Er³⁺ spin relaxation and magnetic coupling in ErNi₂B₂C, Er(Ni_0.975Co_0.025)₂B₂C and Er_0.2Y_0.8Ni₂B₂C from ¹⁶⁶Er Mössbauer measurements

¹ DRECAM-SPEC, Centre d'Études de Saclay, 91191 Gif-sur-Yvette, France
² National Institute for Metals, 1-2-1 Sengen, Tsukubara, Ibaraki, 305 Japan
³ LCMTR-CNRS, Groupe des Laboratoires de Thiais, rue Henri-Dunant, 94320 Thiais, France
⁴ Institut für Experimentalphysik, TU Wien, 1040 Wien, Austria
⁵ IRI. T-U Delft, 2629 JB Delft, The Netherlands

Received: 12 July 1999
Revised: 14 March 2000
Published online: 15 August 2000

Abstract

In a previous study of the Er³⁺ spin relaxation rate in ErNi₂B₂C (Bonville et al., Z. Phys. B 101, 511 (1996)), we found that its thermal dependence showed an anomaly at the superconducting transition temperature (T_c = 10.5 K). This behaviour could be related either to a superconductivity-related change in the density of conduction band states to which the Er³⁺ spin is coupled or alternatively to the slowing down of the Er³⁺ spin fluctuations due to the development of short range magnetic order above the long range ordering temperature (T_N ∼ 6 K). To identify the origin of the anomaly, we compared the results of a ¹⁶⁶Er Mössbauer study on Er(Ni_0.975Co_0.025)₂B₂C where T_c is depressed to 4 K and T_N remains near 6 K, and on Er_0.2Y_0.8Ni₂B₂C where T_c = 14.2 K and there is no long range order. We conclude the relaxation anomaly is due to the onset of short range magnetic order. The normal state coupling of the 4f-conduction electron exchange in the partially diluted sample is = 0.015. We also present ¹⁶⁶Er Mössbauer measurements of the hyperfine field in single crystal ErNi₂B₂C which provide information concerning the direction of the magnetically ordered Er³⁺ moments in the superconducting phase.