Low-temperature thermal conductivity and magnetic transitions of the kagome-staircase compound Ni3V2O8

Abstract

The kagome-staircase compound ${\mathrm{Ni}}_{3}{\mathrm{V}}_{2}{\mathrm{O}}_{8}$ is an attractive multiferroic material exhibiting rich phase diagrams. However, the magnetic properties and magnetic transitions have been studied only above 1.3 K. In this work, we study the thermal conductivity $\ensuremath{\kappa}$ of ${\mathrm{Ni}}_{3}{\mathrm{V}}_{2}{\mathrm{O}}_{8}$ single crystals at low temperatures down to 0.3 K and in magnetic fields up to 14 T. In zero field, the magnetic transitions from the low-temperature incommensurate (LTI) phase to the commensurate phase (C) and then to a second commensurate phase $({\mathrm{C}}^{\ensuremath{'}})$ yield anomalies in $\ensuremath{\kappa}(T)$ curves at ${T}_{\mathrm{LC}}=3.7$ K and ${T}_{{\mathrm{CC}}^{\ensuremath{'}}}=2.0$ K, respectively, which indicates a significant phonon scattering by the critical spin fluctuations. When the field is applied along the $a$ axis, the field dependence of $\ensuremath{\kappa}$ displays four anomalies associated with different magnetic transitions and reveals an undetected magnetic state at subkelvin temperatures. In addition, the $\ensuremath{\kappa}(B)$ curves are found to depend not only on the history but also on the magnitude of the applied field. When the field is applied along the $b$ axis, a high-field phase located above the LTI and high-temperature incommensurate phases is revealed.