Investigation of static and dynamic magnetic properties of Ni0.85Mg0.15Cr2O4 nanoparticles

Ni _0.85Mg _0.15Cr ₂O ₄ nanoparticles with average particle size of 46 nm were synthesized by hydrothermal route. Rietveld refinement reveals single phase cubic crystal structure with lattice constant 8.3560(6) Å. Temperature variation of magnetization measurements suggests multiple magnetic transitions in the compound. The low temperature peak observed around 10 K is attributed to a surface cluster glass like transition based on detailed relaxation, memory effect, field and temperature dependent magnetization measurements. In contrast to the canted spin structure of bulk NiCr ₂O ₄, the core spin structure of the nanoparticle system is showing tendency towards collinear ferrimagnetism. This leads to the suppression of ordering of transverse (antiferromagnetic) components of magnetic structure as typically observed in bulk NiCr ₂O ₄ . Various memory and relaxation protocols were followed in order to study the dynamics of the nanoparticles. We have observed asymmetric response of magnetic relaxation with respect to change in temperature below the glassy transition temperature.