Particle size effects in the antiferromagnetic spinel CoRh

We report the particle size dependent magnetic behaviour in the antiferro-magnetic spinel CoRh 2 O 4. The nanoparticles were obtained by mechanical milling of bulk material, prepared under sintering method. The XRD spectra show that the samples are retaining the spinel structure. The particle size decreases from 70 nm to 16 nm as the milling time increases from 12 hours upto 60 hours. The magnetic measurements suggest that the antiferromag-netic ordering at T N ≈ 27K exists in bulk as well as in nanoparticle samples. However, the magnitude of the magnetization below T N increases with decreasing particle size. Considering the fact that Rh 3+ has strong octahedral (B) site occupation and no change in T N of bulk and nanoparticle samples, we believe that the observed magnetic enhancement is not related to the cationic redistribution between tetrahedral (A) and octahedral (B) sites of the spinel structure. In our opinion, the observed effect is a consequence of decreasing coherent length of antiferromagnetic coupled core spins and increasing number of the frustrated shell in the core-shell model of anoparticle.