Influence of tungsten substitution on structure, optical, vibrational and magnetic properties of hydrothermally prepared NiFe2O4

Abstract

A series of single-phase NiFe2O4 powder with different W-doping (0.0 ≤ x ≤ 0.2) has been synthesized using hydrothermal processing route. The change in lattice parameter and magnetic properties with W-doping was correlated with the change in the occupancies of tetrahedral and octahedral sites with Fe(III) ions resulting from competence between Fe(III) and W(VI) ions. The total magnetic moment increases and the lattice parameter decreases with W-doping up to x = 0.1 (Ms = 49.0 emu/g). However, the lattice parameter increases and the total magnetic moment dramatically decreases to 27.0 emu/g with x = 0.2 doping. The microstrain (e) increases with increasing the level of W(VI) ion substitution. The e of pure NiFe2O4 sample is 3.5 × 10–3 and it increases to 9.7 × 10–3 for NiW0.2Fe1.6O4 (x = 0.2). The increase in e is due to the difference in ionic sizes of W(VI) an Fe(III) and the formation of cation vacancies. The latter is formed because W(VI) ion substituted for two Fe(III) ions, so that the produced ferrite will have the general formula; NiWxFe2-2xO4. The band gap slightly increases with increasing the increasing the level of W-doping.