Enhanced structure and magnetic properties of doped nanomagnetite by γ-irradiation

Highlights: • Grain size of Mn and Co doped magnetite increased due to the ferric to ferrous ions. • Grain size for pure and Ni decreased due to the ions reside on the grain boundary. • γ-irradiation increases the coercivity for all samples of transition metal type. • For Ni doped magnetite; irradiation causes increase, 2.4 times, in the coercivity. • γ-irradiation increase Curie temperature, i.e. more thermally stable magnetization. Nanocrystalline magnetite M_xFe_3-xO₄ at x = 0.0 (pure magnetite) and M = Mn²⁺, Co²⁺, Ni²⁺ at x = 0.3 were prepared by co-precipitation method. The structural, morphological, and magnetic properties were examined before and after gamma -irradiation with energy 1.17 MeV. The sample crystallinity was clearly affected by the irradiation as indicated by comparing the XRD patterns. The irradiation also changed the unit cell volume and the crystallite size of the samples. Transformation of ferric to ferrous ions as a consequence of irradiation leads to an increase in Mn-doped magnetite lattice parameter. However, the cation redistribution in the other samples, including the undoped magnetite, results in a drop of their lattice parameter after γ-irradiation. The morphology is obviously different for the pristine and irradiated samples. Moreover, the irradiation has a direct effect on the coercivity especially for Co and Ni doped magnetites and was attributed to a consequence of surface and shape anisotropy respectively.