Ground-state magnetism of chromium-substituted LiMn2O4 spinel

Abstract

Comparative crystal structure and magnetic properties studies have been conducted on quaternary powder spinel samples LiMn1.82Cr0.18O4 obtained by two different synthesis methods, glycine-nitrate (GN) and ultrasonic spray-pyrolysis (SP). Although both samples possess the same spinel structure of the cubic space group Fd (3) over barm, their low-temperature magnetic properties display significant differences. While the SP sample undergoes only spin-glass transition at the freezing temperature T-f 20 K, the GN sample possesses more complicated low-temperature magnetic behavior of the reentrant spin-glass type with the Neel temperature TN 42K and freezing temperature Tf 22 K. High-temperature magnetic susceptibility of both samples is of the Curie-Weiss type with the effective magnetic moments in agreement with the nominal compositions. This fact together with the results of the chemical analysis discards the existence of the diversity in chemical compositions as a possible cause for the observed differences in the low-temperature magnetism. On the other hand, the crystal structure analysis done by the Rietveld refinement of the X-ray powder diffraction data points to the strong influence of the cation distribution on the ground-state magnetism of these systems. An explanation of this influence is proposed within the framework of a collective Jahn-Teller effect. (C) 2007 Elsevier B.V. All rights reserved.