Size dependence of the magnetic order in antiferromagnetic Cr2O3 nanoparticles

D. TOBIA; E. WINKLER; R.D. ZYSLER; M. GRANADA; H.E. TROIANI

Karlsruhe

Congreso; The International Conference on Magnetism - ICM 2009; 2009

IUPAP

The magnetic properties are determined by the effective exchange and anisotropy fields which are strongly modilied by the surface to volume ratio (PRB 78, 104412 (2008)). In this work we study the magnetic behaviour of antiferromagnetic Cr203 nanoparticles systems with sizes between 8 and 70 nm. The samples characterization was performed by x-ray diffraction and transmission electron microscopy, the magnetic properties were investigated by magnetization and electron paramagnetic resonance experiments. We have found a significant decrease of the Néel temperature (TN) to 270 K when the size is reduced ( TNbulk= 307.8 K). As a function of the particle size the effective anisotropy decreases from the bulk value, Kbulk = 3.8 10^4 erg/g, shows a minimum at ~30 nm (K = 8.7 l0^2 erg/g) and increases for smaller sizes. For example for particles of 8 nm, K = 8.3 l0^3 erg/g. We analyze the size dependence of K in terms of the magnetocrystalline and surface anisotropy contributions.