Neutron diffraction study and temperature variation of magnetic anisotropy in Bi substituted nickel ferrite

Bismuth doped NiFe2O4 (NFO) polycrystalline samples: Ni1-xBixFe2O4 with x = 0.00, 0.05 and 0.10, were synthesized using solid-state reaction method. The crystal structural, magnetic structure and magnetic properties of parent NFO and Bi-doped NFO samples were characterized using X-ray diffraction (XRD), neutron powder diffraction (NPD) and magnetization (M) versus magnetic field (H) isotherms, respectively. Rietveld refinement of XRD and NPD patterns confirms the formation of a single-phase cubic spinel crystal structure. No observable change in the lattice parameter was found (within the error limits) with the 5 at % Bi doping to NFO, whereas approximate to 0.15% change in the lattice parameter was observed in case of 10 at % Bi-doped NFO. Room temperature magnetic structure studies using NPD reveal a net magnetic moment of 1.55(3) mu(B)/f. u., in the case of NiFe2O4. The net magnetic moment at room temperature changes to 1.61(4) mu(B)/f.u. and 1.47(5) mu(B)/f.u. for Ni0.95Bi0.05Fe2O4 and Ni0.90Bi0.10Fe2O4, respectively. The same observation was also inferred from the spontaneous magnetization (M-sp) obtained from approach-to-saturation (ATS) analysis of M-H isotherms. Temperature (T) dependence of M-sp follows a T-2 decline. Approximately 14% increase in magnetic anisotropy was observed in Ni0.95Bi0.05Fe2O4 compared to NiFe2O4 in the temperature range 5 K -300 K.