Spin-Fluctuation Effects near the Quantum Phase Transition of the Ising-Type Itinerant Ferromagnet URhAl

We performed high-pressure resistivity measurements for an Ising-type itinerant ferromagnet URhAl at low temperatures down to 40 mK. In URhAl, the Curie temperature (T-C) is sufficiently suppressed with increasing pressure and T-C suddenly disappears at the critical pressure P-c similar to 5.2 GPa. Above P-c, we observed the large enhancement of the A coefficient of AT(2) resistivity term, which is defined below T*(P). Near P-c, the exponent (n) of resistivity, rho(T) = rho(0) + A'T-n, approaches n similar to 5/3, which is suggested from the spin-fluctuation theory for a three dimensional itinerant ferromagnetic system. We observed the non-Fermi-liquid behavior of resistivity under high pressure far above Pe up to 7.5 GPa. On the other hand, the critical behaviors of T*(P) and A(P) for URhAl do not obey the spin-fluctuation theory for a ferromagnetic quantum critical point, where the Curie temperature vanishes as a second-order phase transition. The sudden disappearance of T-C support the change of nature of transition from second order to first-order in URhAl near P-c. Furthermore, the pressure dependences of A(P) and rho(0)(P) are asymmetric around P-c, and these behaviors might be explained by a remarkable Fermi-surface change, which accompanies the ferromagnetic-paramagnetic quantum phase transition in URhAl.