Intercalation and Substitution Effects of Si in Weak Itinerant Ferromagnetic Ni3Al

The Si-intercalated compounds Ni3AlSix (x = 0, 0.01, 0.02, 0.05, 0.07, and 0.1) and Si substituted compounds Ni3Al1-ySiy (y = 0, 0.01, 0.015, 0.02, 0.04, 0.06, 0.1, and 0.2) were synthesized and investigated by macroscopic and microscopic magnetic measurements. We found that the common features to these two systems are: (i) drastic disappearance of ferromagnetism in Ni3Al with only a small Si concentration x(c) similar or equal to 0.01 or y(c) similar or equal to 0.02, (ii) T-4/3 -temperature dependences in both square spontaneous magnetization M(0, T)(2) and inverse initial susceptibility chi(-1)(0) near the Curie temperature T-C for ferromagnetic metal. T-4/3 -temperature dependence of chi(-1)(0) are found to hold even for the paramagnetic metals that are classified as nearly itinerant ferromagnets very close to the ferromagnetic instability. On the other hand, our Al-27 NMR results show that the Si intercalation leads to the changes of the hyperfine coupling constant A(hf), the characteristic parameters of spin fluctuations, T-0 and T-A. These results indicate that the Si intercalation modify not only the density of states at the Fermi level but also the magnetic instability as well as the spin-fluctuation spectrum of Ni3Al. These results can be understood in the frame of the self-consistent renormalization (SCR) theory and the Takahashi theory of spin fluctuations.