Mechanosynthesis, magnetic and Mössbauer characterization of pure and Ti⁴⁺-doped cubic phase BiFeO₃ nanocrystalline particles

The mechanosynthesis of cubic γ-phase pure BiFeO₃ and Ti⁴⁺-doped BiFeO₃ nanocrystalline particles and their preliminary characterization with magnetic measurements and Mössbauer spectroscopy are reported. The BiFeO₃ nanoparticles (5-40 nm) were prepared by heating a 48 h pre-milled 1:1 molar mixture of α-Bi₂O₃ and α-Fe₂O₃ at 400 °C for (1 h). Doping α-Fe₂O₃ in the initial mixture of reactants with Ti⁴⁺ was found to lead to the formation of Ti⁴⁺-doped BiFeO₃ nanoparticles by milling the reactants for 32 h. The magnetization of the BiFeO₃ nanoparticles is found to be tripled under a maximum external field of 1.35 T and their magnetic hardness increases by ∼15 times relative to those of the corresponding bulk. The Ti⁴⁺-doped BiFeO₃ nanoparticles exhibit higher magnetization relative to the pure ones. These observations are related to the spiral modulated spin structure of the compound. The Mössbauer data show ∼12 % of the BiFeO₃ nanocrystalline particles to be superparamagnetic having blocking temperatures of less than 78 K. The quadrupole shift values of the magnetic spectral component favor the cubic structural symmetry. These observations were mainly associated with possible collective magnetic excitations as well as transverse relaxation of canted surface spins. The Ti-doped BiFeO₃ nanoparticles gave statistically-poor Mössbauer spectra with no signs of a superparamagnetic behavior.