Anomalous Metal-Insulator Transition in BaCo1?xNixS2?y as a Triggered Phase Transition

Abstract

Subject classification: 71.30.+h; 75.30.Kz; S8.16 The anomalous metal-insulator transition in BaCo 1--x Ni x S 2--y is identified as a triggered phase transition based on strong coupling between a magnetic and a structural order parameter. In particular, we observe a second-order paramagnetic-antiferromagnetic transition at T N followed by a first-order metal-insulator transition at T MI . The field-induced shifts of the sequential transition temperatures are determined for y ¼ 0.05: dT N /dB ¼ (--0.8 AE 0.2) K/T, and (--0.1 AE 0.1) K/T dT MI /dB (--0.5 AE 0.1) K/T.