Increased exchange interaction range by Fe substitution in Ni3-xFexAl: Evidence from critical behavior

The critical behavior of Fe substituted intermetallic compounds Ni _3-xFe _xAl (x = 0, 0.18, and 0.36) has been investigated around the paramagnetic-ferromagnetic (PM-FM) phase transition based on the static magnetization data. Reliable critical exponents (β, γ, and δ) and transition temperature T _C are determined for the compounds, by using Modified Arrott plot, Kouvel-Fisher plot, and critical isotherm plot. The self-consistence and reliability of the obtained critical exponents are further verified by the Widom scaling relation δ = 1 + γ/β and scaling equations of the state M(H,ε) = ε ^β f _±(H/ε ^β+γ). It is found that, Fe substitution for Ni dramatically increases T _C from 44.44 K for x = 0 to 301.20 K for x = 0.36. The critical exponents for the three compounds are all found to follow mean-field model. The exchange interaction J(r) is found to decay as r - 4.657 _, r - 4.434 , and r - 4.257 for x=0, 0.18 and 0.36, respectively. The results suggest that, a long range mean-field spin interaction dominates in Ni _3-xFe _xAl (0≤x≤0.36) series. Furthermore _, Fe substitution to Ni site is found to increase the spin interaction distance to longer range.