Effects of Ni substitutions on the critical behaviors in Nd0.6Sr0.4Mn1−xNixO3 manganite

We investigate the effect of Ni-substitution on the crystalline structure and the critical behavior of Nd_0.6Sr_0.4Mn_1−xNi_xO₃ (0.00 ≤ x ≤ 0.20) perovskite. X-ray diffraction patterns revealed that the major phase in all samples is the orthorhombic structure with space group Pnma. Rietveld refinement revealed a linear reduction in the lattice parameters along with monotonic reduction in the O2-Mn-O2 angel with increasing Ni concentration. The modified Arrott plots and the Kouvel-Fisher method have been used to analyze the magnetization isotherms near the paramagnetic to ferromagnetic (PM-FM) phase transition. The obtained critical exponents (β, γ and δ) revealed that the Ni-free sample is consistent with 3D-Heisenberg like behavior. However, upon Ni-substitution, the critical exponents exhibit a mean field like behavior. The reliability of the obtained critical exponent (β, γ, and δ) values have been confirmed by the universal scaling behavior of the isothermal magnetization near the transition temperature.