Evidence for logarithmic corrections to the mean-field critical behavior in the weak itinerant ferromagnet Ni₃Al

Abstract

The results of an elaborate analysis of high-resolution magnetization and ac suceptibility data unambiguously establish the existence of multiplicative logarithmic corrections (MLC) to single power laws in the asymptotic critical region near the ferromagnetic-paramagnetic phase transition in well-characterized polycrystalline Ni₃Al samples. A crossover from this asymptotic critical behavior to the Gaussian fixed point occurs gradually over a fairly wide temperature range outside the critical regime. Accurate determination of the universal amplitude ratio Rχ=DB^δ-1Γ, the asymptotic critical exponents β , γ , and δ and the MLC exponents x^-, x⁺, and x⁰ for spontaneous magnetization, initial susceptibility and the magnetization versus field isotherm at T=T_C (the Curie temperature), respectively, and a detailed comparison between theory and experiment indicate that the weak itinerant ferromagnet Ni₃Al, so far as its asymptotic critical behavior is concerned, is an experimental realization of an isotropic d=3, n=3 ferromagnet in which the interactions between magnetic moments decay with distance (r) as J(r)~ 1/r^(3/2)d.