Disorder-induced orbital glass state in FeCr₂S₄

¹  Key Laboratory of Materials Physics, Institute of Solid State Physics, Chinese Academy of Sciences Hefei 230031, PRC
²  National High Magnetic Field Laboratory, University of Science and Technology of China - Hefei 230026, PRC

Corresponding author: zryang@issp.ac.cn

Received: 3 November 2009
Accepted: 17 February 2010

Abstract

The effect of disorder on the orbital state in the spinel FeCr₂S₄ has been investigated with the substitution of Cr by Al, Ga, and Fe, respectively. For polycrystalline FeCr₂S₄, being related to the orbital-ordering transition around 9 K, the temperature dependence of magnetization shows a step-like transition, and the specific heat displays a well-defined λ-type anomaly correspondingly. However for single-crystal and doped FeCr₂S₄ samples, the step-like transition in magnetization disappears, and the λ-type anomaly of specific heat is replaced by a broad hump. Moreover, the specific heat obeys a T²-dependence at temperatures below 2 K, suggesting the formation of the orbital glass state in these samples. Consistently with different orbital states, the resistivity at low temperature can be better fitted with a thermally activated model for the polycrystalline FeCr₂S₄ sample, and better described by Mott's variable-range hopping expression for the others. All these results imply that the disorder induces orbital glass state in FeCr₂S₄.