Ru-NMR Studies and Specific Heat Measurements of Bi₃Ru₃O₁₁ and La₄Ru₆O₁₉

Abstract

Specific heats measurements and Ru-NMR studies have been carried out for Bi₃Ru₃O₁₁ and La₄Ru₆O₁₉, which commonly have three-dimensional linkages of edge-sharing pairs of RuO₆ octahedra. The Knight shifts, the nuclear spin–lattice relaxation rates 1⁄T₁ and the electronic specific heats C_el of these systems exhibit anomalous temperature (T) dependence at low temperatures, as was pointed out by Khalifah et al. [Nature 411 (2001) 660.] for the latter system based on their experimental data of the resistivity, magnetic susceptibility and electronic specific heat. Ratios of 1⁄T₁T to the square of the spin component of the isotropic Knight shift, K_spin estimated for these systems at low temperatures suggest that they have antiferromagnetic (AF) spin fluctuations. It is confirmed by the fact that the T-dependences of 1⁄T₁T and C_el⁄T of the present systems can be explained by the self-consistent renormalization theory for three dimensional itinerant electron systems with AF spin fluctuations. All these results suggest that the AF fluctuations are the primary origin of the characteristics of their low temperature physical behavior.