Low-temperature thermal conductivity and magnetic transitions of the kagomé-staircase compound Ni${}_3$V${}_2$O${}_8$

Abstract

Kagomé-staircase compound Ni${}_3$V${}_2$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 ($\hat{I}º$) of Ni${}_3$V${}_2$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 (C') yield anomalies in $\hat{I}º(T)$ curves at $T{}_{\mathrm{LC}}$ = 3.7 K and $T{}_{\mathrm{C}{\mathrm{C}}^{\prime }}$ = 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 $\hat{I}º$ displays four anomalies associated with different magnetic transitions and reveals an undetected magnetic state at subKelvin temperatures. In addition, the $\hat{I}º(B)$ curves are found to depend not only on the history but also on the magnitude of applying field. When the field is applied along the $b$ axis, a high-field phase locating above the LTI and high-temperature incommensurate (HTI) phases is revealed.

9 pages, 12 figures, accepted for publication in Phys. Rev. B