Spin-driven crystal lattice distortion in frustrated magnet CuFeO2:: Synchrotron X-ray diffraction study

We have performed synchrotron radiation X-ray diffraction measurement,,, on a triangular lattice antiferromagnet CuFeO2 using the single crystal. The crystal lattice symmetry lowers from hexagonal to orthorhombic below the magnetic phase transition (from a partially disordered phase to four-sublattice phase) temperature T-N2. In addition, superlattice reflections were observed below TN2; this suggests that the "scalene triangle model" lattice distortion splits the nearest neighbor exchange interaction in the basal plane into three different exchange interactions. This distortion lifts the vast degeneracy of the strongly frustrated spin system, leading to the four-sublattice ground state. Thus we argue that the lattice degree of freedom plays an important role in the stabilization of the four-sublattice ground state in CuFeO2.