Structure and physical properties ofSrNiRu5O11single crystals: AnR-type ferrite based on ordered kagome nets

Abstract

Single crystals of the $R$-type ferrite $\mathrm{SrNiR}{\mathrm{u}}_{5}{\mathrm{O}}_{11}$ were grown from a chloride flux. The hexagonal crystal structure contains ruthenium located on distorted kagome nets. The low-temperature dc magnetic susceptibilities (${\ensuremath{\chi}}_{\ensuremath{\perp}}$ and ${\ensuremath{\chi}}_{\ensuremath{\parallel}}$, perpendicular and parallel to the $\mathbit{c}$ axis, respectively) diverge as ${T}^{\ensuremath{-}0.3}$, and do not exhibit any indication of long-range magnetic order down to 4.5 K. The electrical resistivity varies as ${T}^{1.6}$ below 40 K, which is typical of non-Fermi liquids, and may originate from a competition between residual magnetic interactions among $\mathrm{N}{\mathrm{i}}^{2+}$ ($S=1$) spins and geometrical frustration on the two-dimensional kagome lattice of $\mathrm{R}{\mathrm{u}}^{3+}$ ($S=\textonehalf{}$) spins. The transverse magnetoresistivity ${\ensuremath{\rho}}_{xy}$ at constant temperature $T=5\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ for current ($\mathbit{J}$) -magnetic field ($\mathbit{H}$) configurations, $\mathbit{J}\ensuremath{\perp}\mathbit{H}\ensuremath{\parallel}\mathbit{c}$ axis and $\mathbit{J}\ensuremath{\parallel}\mathbit{H}\ensuremath{\perp}\mathbit{c}$ axis, reveals no anomalous contribution, which is consistent with the absence of magnetic order. Fits of the specific heat data below 10 K require a dominant, but unusual electronic term of the form ${C}_{el}=\ensuremath{\gamma}{T}^{1.2}$, which is expected for massless Dirac fermion states in topological insulators, or spin-liquid phases.