Spin dynamics of triangular lattice antiferromagnet CuFeO_2: Crossover from spin-liquid to paramagnetic phase

摘要

We have investigated the spin dynamics of triangular lattice antiferromagnet CuFeO_2 by measuring powder neutron inelastic-scattering spectra. A quasielastic component whose half-width oscillates with the magnitude of the scattering vector appears in the spectra above Neel temperature. A dynamics model representing the shape of quasielastic components and oscillatory behaviors changes from spin jump diffusion to Heisenberg paramagnetic (PM) scattering with increasing temperature. These findings demonstrate that CuFeO_2 shows a gradual transition from a spin-liquid phase to the Heisenberg PM phase. The origin of the spin-liquid phase is discussed in terms of incommensurate short-range spin correlation.