Restoring Higher Symmetric Crystal Structure with Magnetic Field in Triangular Lattice Antiferromagnet CuFeO2

Structural deformations associated with magnetic phase transitions have been studied by synchrotron radiation X-ray diffraction in high magnetic fields up to 14 T for the geometrically frustrated triangular lattice antiferromagnet CuFeO 2 . When a magnetic field is applied along the hexagonal c -axis, "scalene triangular" (ST) lattice distortion, which causes the three different exchange interaction paths in the basal plane, is successively relieved at the critical fields corresponding to field-induced magnetic phase transitions. In particular, the ST lattice is deformed into the higher symmetric "isosceles triangular" lattice at the second-field-induced magnetic phase transition (∼13.5 T). We thus conclude that the spontaneous lattice distortion in CuFeO 2 , which occurs without any orbital degrees of freedom, originates from a magnetoelastic coupling produced by spin frustration.