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 ${\mathrm{CuFeO}}₂$ under applied uniaxial pressure $p$ up to 600 MPa. We found that the phase-transition temperature ${T}_{\mathrm{N}1}$ from the paramagnetic phase to the partially disordered phase increases by as much as 5 K from the original ${T}_{\mathrm{N}1}\ensuremath{\simeq}14\phantom{\rule{4pt}{0ex}}\mathrm{K}$ under applied $p$ of 600 MPa, and that the lattice constant ${b}_{\mathrm{m}}$ of ${\mathrm{CuFeO}}₂$ changes significantly. In contrast, the value of ${q}₀$, which is the magnetic modulation wave number at ${T}_{\mathrm{N}1}$ 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 ${\mathrm{CuFeO}}₂$. These results suggest that a lattice degree of freedom via a spin-lattice coupling is indispensable for the determination of the magnetic properties of ${\mathrm{CuFeO}}₂$. A dielectric anomaly under applied $p$ of 600 MPa is also briefly discussed.