Hidden Symmetry and Mutiferroicity in a Triangular Spin Lattice With Proper-Screw-Spin Chain Order

The multiferroicity in a triangular spin lattice with proper-screw-spin chain order was explored by performing density functional calculations for AgCrO2 and analyzing the symmetry of the magnetic structure of the triangular spin lattice. Strong geometric spin frustration exists within and between CrO2 layers, and the ferroelectric polarization originates from the spiral-spin chain structures propagating across the proper-screw-spin chains. The triangular spin lattice can have ferroelectric polarization parallel to its mirror plane due to hidden symmetry.