Critical behavior and non-universal low-field magnetic scaling in La_1-xBi_xMnO₃ (x=0.4 & 0.6) perovskite manganite oxide

We report on critical behavior in La_1-xBi_xMnO₃ (x=0.4 & 0.6) perovskite manganite oxide by studying AC susceptibility, χ, measured at randomly chosen low magnetic fields (H=9.45 Oe to 0.95 Oe) at fixed frequency of f=131 Hz. The samples exhibit non-uniformity in their magnetic spin interactions around paramagnetic-to-ferromagnetic transition temperature (T_C). By non-universal low-field magnetic scaling of AC χ given as, χ⁻¹-χ⁻¹(T_C) ∼ (T/T_C−1)^γ ≡ τ^γ the magnetic interactions in the samples around T_C has been studied. The linear fit to ln (χ⁻¹ - χ_C⁻¹) vs. ln (T/T_C-1) gives the values of critical exponent ‘γ’ under applied magnetic fields. The values of γ is found to be ∼1.48±0.007 for the sample with x=0.4 and ∼1.36±0.004 for x=0.6 at 0.95 Oe lie in the context of 3D Heisenberg type spin interactions. The profound 3D Heisenberg type spin interactions arises due to the phase separation effect for x=0.4 and breaking of ferromagnetic order and induced Bi³⁺ (6S²) − O²⁻ (2P⁶) lattice distortions for x=0.6 as discussed in manuscript.