Temperature dependent structural phase transitions of the triangular lattice compound AgCrSe2, a frustrated metallic magnet

The triangular lattice compound AgCrSe2 shows exciting and unusual magnetic and transport properties that are up to now only partially understood, in particular it's recently observed anomalous Hall effect. The system is a non-collinear antiferromagnet with TN~32K. But despite sizeable spin-orbit coupling due to the magnetic exchange via Se, the observed anomalous Hall conductivity should be symmetry forbidden in the published R3m crystal structure (no inversion symmetry). However, the physical properties, in particular the transport, are strongly dependent on the exact composition of the compound. We suggest an investigation of the crystal structure of samples with well characterised composition (stoichiometric vs. Ag-poor) down to temperatures below TN and above T~450K (transition to R-3m with restored inversion symmetry). A composition dependent additional symmetry breaking in analogy to the Ag(Cu)CrS2 sister compounds could explain the observed spectacular physical properties.