Magneto-elastic coupling and unconventional magnetic ordering in triangular multiferroic AgCrS2

摘要

The temperature evolution of the crystal and magnetic structures offerroelectric sulfide AgCrS2 have been investigated by means of neutronscattering. AgCrS2 undergoes at TN = 41.6 K a first-order phase transition,from a paramagnetic rhombohedral R3m to an antiferromagnetic monoclinicstructure with a polar Cm space group. In addition to being ferroelectric belowTN, the low temperature phase of AgCrS2 exhibits an unconventional collinearmagnetic structure that can be described as double ferromagnetic stripescoupled antiferromagnetically, with the magnetic moment of Cr+3 oriented alongb within the anisotropic triangular plane. The magnetic couplings stabilizingthis structure are discussed using inelastic neutron scattering results.Ferroelectricity below TN in AgCrS2 can possibly be explained in terms ofatomic displacements at the magneto-elastic induced structural distortion.These results contrast with the behavior of the parent frustratedantiferromagnet and spin-driven ferroelectric AgCrO2.