Mechanically alloyed ${\mathrm{Co}}_{0.2}{\mathrm{Zn}}_{0.8}{\mathrm{Fe}}_2{\mathrm{O}}_4$ nanoparticle has shown the enhancement of both magnetization and ferrimagnetic order which seems to be unusual according to the existing core-shell model of ferrimagnetic nanoparticle. Many concurrent effects such as site exchange of cations among A and B sites, and reduction of B site spin canting have been identified for such unusual magnetic enhancement. We do observe the usual superparamagnetic relaxation effect for the smaller particles. The annealing of the alloyed nanoparticle results in grain growth kinetics and the appearance of mixed magnetic state, similar to the bulk material, for larger particles. In addition, large strain induced anisotropy of as-alloyed nanoparticle sharply decreases during thermal activated grain growth process and anisotropy remains almost constant for larger particles. The present work is focused on the effect of strain-induced anisotropy to control grain boundary magnetic contributions and subsequently, over all magnetization in mechanically alloyed ${\mathrm{Co}}_{0.2}{\mathrm{Zn}}_{0.8}{\mathrm{Fe}}_2{\mathrm{O}}_4$ nanoparticles.

• Received 16 August 2004

DOI:https://doi.org/10.1103/PhysRevB.72.094405