Magnetic phase diagrams of the multicritical olivine Mn2SiS4 and Mn2GeS4

Abstract

Using single crystal neutron diffraction, we studied the H(parallel to b)-T phase diagram of the antiferromagnetic olivine Mn(2)AS(4) (A=Si; Ge). We identified the two spin-flop phases at high fields that are separated by field-independent phase boundaries terminated at multicritical points. In the low temperature phase, the magnetic structures consist of antiferromagnetic C-z-C-z' and ferromagnetic F-x' components. In the high temperature phase, incontrast, they are replaced by C-x-C-x' and F-z'. The absence of the anomalies in the DC magnetization data across the spin-reorientation transitions is discussed in terms of the Clausius-Clapeyron relation. (C) 2009 Elsevier B.V. All rights reserved.