Quantum Critical Phenomena in Ni$_{3}$Al$_{1-x}$Ga$_{x}$ Alloys*

Considerable study has been devoted to quantum phase transitions (QPTs), which are believed to be a key concept for understanding the physics of strongly correlated electrons. In this talk we report on observation of quantum critical phenomena in Ni$_{3}$Al$_{1-x}$Ga$_{x}$ alloys. Ni$_{3}$Al is a ferromagnetic metal with $T_{c} =41.5K$. With Ga substitution for Al, $T_{c}$ and the spontaneous magnetic moment are gradually suppressed down to zero near the critical composition of $x_{c} \quad \sim $ 0.4. We found that near the critical composition the magnetization as a function of magnetic field M(H) and the magnetic susceptibility as a function of temperature \textit{$\chi $}($T)$ both obey the scaling laws theoretically expected for QPTs, i.e., $M(H) \quad \propto $ $H^{1/3}$ and \textit{$\chi $}$^{-1}\propto T^{4/3}$. In addition, we observed that near $x_{c}$ the derivative derived from the Arrott plots, i.e., \textit{$\gamma $=d(M}$^{2})/d(H/M)$ value$, $exhibits a remarkable peak at about 2-3 T. This peak enhances with decreasing temperature. In terms of a recent theory, we argue that \textit{$\gamma $} reflects characteristics of spin excitation spectrum near QPTs.