Possible observation of quantum ferromagnetic fluctuations in La4 Ru6 O19

We report electrical and magnetotransport measurements on La4 Ru6 O19 that was found previously to feature metal-metal bonding and non-Fermi-liquid behavior. Our measurements showed that the transverse and longitudinal magnetoresistance grew rapidly below 30 K. Moreover, the longitudinal magnetoresistance is larger than the transverse magnetoresistance measured at the same temperatures (T) and the sign of the magnetoresistance is negative, suggesting the presence of ferromagnetic fluctuations in La4 Ru6 O19. However, as T was lowered further to below T =4K, the magnetoresistance was found to change its sign from negative to positive. The Hall coefficient, which is negative and strongly temperature dependent, reaches a maximum in its absolute value near T. Most importantly, the resistivity ρ was found to follow the non-Fermi-liquid dependence of ρ∼ T3/2 below T in zero magnetic field and the Fermi-liquid behavior ρ∼ T2 in a high magnetic field. We suggest that these observations can be explained by the existence of ferromagnetic quantum criticality in La4 Ru6 O19 near ambient pressure.