A27lNMR studies of itinerant electron ferromagneticNi3AlCx

Abstract

Carbon-intercalation effects on weakly ferromagnetic ${\text{Ni}}_{3}\text{Al}$ have been studied by $^{27}\text{A}\text{l}$ spin-echo NMR techniques. The Knight shift $K$ and the nuclear spin-lattice relaxation time ${T}_{1}$ of $^{27}\text{A}\text{l}$ have been measured in the carbon-intercalated ${\text{Ni}}_{3}{\text{AlC}}_{x}$ with $x=0$, 0.01, 0.02, 0.05, and 0.1, whose Curie temperatures are 36 K, 18 K, $<2\text{ }\text{K}$, $<2\text{ }\text{K}$ and $<2\text{ }\text{K}$, respectively. The magnitude of the negative $^{27}\text{A}\text{l}$ hyperfine coupling constants were found to decrease at first, and then increase with the carbon intercalation into the body-center site of ${\text{Ni}}_{3}\text{Al}$. The linear relations between the $1/{T}_{1}T$ and the magnetic susceptibility $\ensuremath{\chi}$ indicate that the three-dimensional ferromagnetic spin fluctuations are dominant in the ${\text{Ni}}_{3}{\text{AlC}}_{x}$ 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 $x\ensuremath{\sim}0.02$.