Magnetic ordering dependence of antiferromagnetic Cr2O3 nanoparticles with particle size

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

Rio de Janeiro

Congreso; 9th International Conference on Nanostructured Materials - NANO 2008; 2008

Nano conferences

In this work we present a study of the magnetic properties of antiferromagnetic (AFM) Cr2O3nanoparticles as a function of the nanoparticle size. Cr2O3 presents an antiferromagnetic orderbelow the Néel temperature TN (Bulk) = 307.8 K. In the AFM ordered phase the fourchromium spins in the unit cell are alligned along the threefold axis of the crystal. When ahigh magnetic field is applied to this system the chromium spins flop in the basal plane,maintaining the antiferromagnetic order.Our samples were synthesized by chemical precipitation followed by calcination at different temperatures, from 900 K to 1700 K. TEM images show that the synthesized nanoparticlespresent an ellipsoidal shape with the major axis of approximately 170 nm and the minor axisthat increases with the synthesis temperature from 30 nm to 70 nm. When the dimensions ofthe material are reduced, the magnetic properties are highly modified due to the increase inthe surface to volume ratio. Electron paramagnetic resonance (EPR) experiments togetherwith magnetization measurements allowed us to perform a thorough characterization of theAFM nanoparticles system. We have found that the AFM order temperature and the spin-floptemperature are strongly dependent on the surface effects; they both increase with the particlesize and approach the bulk values for the larger nanoparticles.