Uniaxial Pressure Effects On Spin-Lattice Coupled Phase Transitions In A Geometrical Frustrated Magnet Cufeo2

We performed magnetic susceptibility, dielectric constant, neutron-diffraction, and synchrotron radiation x-ray diffraction measurements on a spin-lattice coupling system CuFeO2 under applied uniaxial pressure p up to 600 MPa. We found that the phase-transition temperature T-N1 from the paramagnetic phase to the partially disordered phase increases by as much as 5 K from the original T-N1 similar or equal to 14 K under applied p of 600 MPa, and that the lattice constant b(m) of CuFeO2 changes significantly. In contrast, the value of q(0), which is the magnetic modulation wave number at T-N1 and which should reflect the ratios of the exchange coupling constants, is not changed, even by applied p of 600 MPa. Based on these results, we show that an explanation using only the exchange striction effect is not suitable for the magnetic phase transition in CuFeO2. These results suggest that a lattice degree of freedom via a spin-lattice coupling is indispensable for the determination of the magnetic properties of CuFeO2. A dielectric anomaly under applied p of 600 MPa is also briefly discussed.