Structure and Physical Properties of SrNiRu\u3csub\u3e5\u3c/sub\u3eO\u3csub\u3e11\u3c/sub\u3e Single Crystals: An \u3cem\u3eR\u3c/em\u3e-Type Ferrite Based on Ordered Kagome Nets

Single crystals of the R-type ferrite SrNiRu5O11 were grown from a chloride flux. The hexagonal crystal structure contains ruthenium located on distorted kagome nets. The low-temperature dc magnetic susceptibilities (χ⊥ and χ∥, perpendicular and parallel to the c axis, respectively) diverge as T−0.3, and do not exhibit any indication of long-range magnetic order down to 4.5 K. The electrical resistivity varies as T1.6 below 40 K, which is typical of non-Fermi liquids, and may originate from a competition between residual magnetic interactions among Ni2+ (S = 1) spins and geometrical frustration on the two-dimensional kagome lattice of Ru3+ (S = ½) spins. The transverse magnetoresistivity ρxy at constant temperature T = 5 K for current (J) -magnetic field (H) configurations, J⊥H ∥ c axis and J ∥ H⊥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 Cel = γT1.2, which is expected for massless Dirac fermion states in topological insulators, or spin-liquid phases