Magnetic properties of ZnFe 2 O 4 and In-doped ZnFe 2 O 4 nanoparticles

The magnetic behaviour of ZhFe 2 O 4 and Zn 0.85 In 0.15 Fe 2 O 4 nanoparticles with diameters of about 4.1 and 3 nm respectively was investigated by dc magnetisation measurements. Both materials are at superparamagnetic state above a blocking temperature of about 25 K and exhibit the collective behaviour of an assembly of single domain ferromagnets below this temperature. In-doping results in a decrease of the magnetisation and increase of coercitivity of the nanoparticles. This observation implies that, besides size, doping causes also significant structural rearrangements which in turn induce changes in the strength and the number of Fe 3+ (A)-O-Fe 3+ (B) superexchange interactions.