Title: Ferromagnetism, Superconductivity and
Quantum criticality in Uranium-based compounds.

Nguyen Thanh Huy - May 06 2008

Abstract

We have investigated the evolution of ferromagnetic order in the correlated 
metal URhGe (Curie temperature TC = 9.5 K) by chemical substitution of Ru and 
Co. In the case of Ru doping, TC of the URh1-xRuxGe series initially 
increases, but then decreases linearly as a function of x and is completely 
suppressed for xcr ≈ 0.38. The ordered moment m0 is suppressed in a 
continuous way with Ru increasing. At xcr, the observed critical behaviors 
provide evidence for a ferromagnetic quantum phase transition. In the case of 
Co doping, the Curie temperature in the URh1-xCoxGe series has a broad 
maximum TC = 20 K near x = 0.6 and then drops to 3 K for x = 1. Surprisingly, 
superconductivity is found to coexist with ferromagnetism at ambient pressure 
for the end-member of the Co-doping series, UCoGe. Magnetization measurements 
show that UCoGe is a weak ferromagnet with a small ordered moment 
m0 = 0.03 μB. Superconductivity is observed with a resistive transition 
temperature TS = 0.8 K for the best sample. The proximity to a ferromagnetic 
instability and the absence of Pauli limiting, suggest triplet 
superconductivity mediated by critical ferromagnetic fluctuations.