Sol-gel synthesized high anisotropy magnetic nanoparticles

The nanoparticles of NiCrxFe2-xO4 were syn- thesized through sol-gel reactions involving nitrates of Ni, Cr and Fe in an aqueous medium containing citric acid. The cubic spinel structure in single phase with nanometric crystallite size of *5 nm, the spherical morphology and magnetic relaxations were examined through XRD, TEM and Mossbauer techniques. The abnormal occurrence of finite remanance (Mr) and coercivity (Hc) resulted in the room temperature dc magnetization measurements for the small particles authenticate the ferrimagnetic regime, as proposed by the room temperature Mossbauer results of the samples, with a proximate superparamagnetic regime still at lower particle volumes. This could be attributed to the antiferromagnetic spin interactions of chromium ions at octahedral sites and subsequently the over-occupancy of the rest of the cations at tetrahedral sites. In justification to this, the magnetocrystalline anisotropy constant, K ,i s estimated to have value relatively high of the order of 10 7 erg/cm 3 at room temperature for all studied concentrations.