Magnetic enhancement in antiferromagnetic nanoparticle of CoRh2O4 -: art. no. 054430

Our magnetic investigation of CoRh2O4 nanoparticles show the signature of antiferromagnetic ordering at T(N)approximate to27 K, same as that of the bulk sample, for all particle sizes down to approximate to16 nm. However, we observe a systematic magnetic enhancement below T-N, being larger for a smaller particle size. We propose a core-shell model for the magnetization of nanoparticles, with the core retaining its antiferromagnetic order and the enhancement of magnetization below T-N attributed to the increasing number of frustrated shell (surface) spins. The scaling analysis of low temperature magnetization shows that the system approaches the limit of superparamagnetism for the particle size similar to8 nm. Our model also predicts an alternation of exchange interactions along the inter-particle distance, very similar to RKKY type interactions in the metallic spin glass systems.