Preparation of nanocrystalline MnFe<SUB>2</SUB>O<SUB>4</SUB> by doping with Ti<SUP>4+</SUP> ions using solid-state reaction route

Nanostructured manganese ferrites (MnFe<SUB>2</SUB>O<SUB>4</SUB>) with diameters in the range of 45-30 nm were synthesized by Ti<SUP>4+</SUP> ion doping, using conventional solid-state reaction route. The substitution of Ti<SUP>4+</SUP> ions created vacancies at Mn<SUP>2+</SUP> sites and the coupling of ferrimagnetically active oxygen polyhedra was broken. This created nanoscale regions of ferrites. A reduction of magnetization for decreasing particle size was observed. Coercivity showed an increasing trend. This was explained as arising due to multidomain/monodomain magnetic behaviour of magnetic nanoparticles. DC resistivities of the doped specimens indicated the presence of an interfacial amorphous phase formed by the nanoparticles. Zero-field cooled and field-cooled curves from 30 nm sized particles showed a peak at T<SUB>B</SUB> (~125 K), typical of superparamagnetic blocking temperature