27Al NMR studies of itinerant electron ferromagnetic Ni3AlCx

Carbon-intercalation effects on weakly ferromagnetic Ni3Al have been studied by Al-27 spin-echo NMR techniques. The Knight shift K and the nuclear spin-lattice relaxation time T-1 of Al-27 have been measured in the carbon-intercalated Ni3AlCx with x=0, 0.01, 0.02, 0.05, and 0.1, whose Curie temperatures are 36 K, 18 K, <2 K, <2 K and <2 K, respectively. The magnitude of the negative Al-27 hyperfine coupling constants were found to decrease at first, and then increase with the carbon intercalation into the body-center site of Ni3Al. The linear relations between the 1/T1T and the magnetic susceptibility chi indicate that the three-dimensional ferromagnetic spin fluctuations are dominant in the Ni3AlCx system. We estimate the evolution of the characteristic temperature of spin fluctuations, T-0, in frequency space when the system changes from weak ferromagnetism to a nearly ferromagnetic state. Then, we analyze the temperature dependence of inverse magnetic susceptibilities and discuss the feature of the spin fluctuations in this system. As a result, the carbon-intercalation effect was found to be over a long range, inducing three-dimensional ferromagnetic quantum phase transition at x similar to 0.02.