Spin-flop transition in Cr2O3 nanoparticles

DINA TOBIA; ELIN WINKLER; ROBERTO ZYSLER; HORACIO TROIANI

Río de Janeiro, Brasil

Workshop; VIII Latin American Workshop on Magnetism, Magnetic Materials and their applications; 2007

The Cr2O3 presents an antiferromagnetic order below the Néel temperature TN = 307.8 K. In the ordered phase the four chromium spins in the unit cell are aligned along the threefold axis of the crystal. In presence of high magnetic field the Cr spins flop in the basal plane maintaining the AFM order. The spin-flop transition develops at HSF = 5.8 T at T = 90 K in the bulk compound. When the dimension of the material is reduced to nanoscale, the magnetic properties are strongly modified by the increase of the surface/volume ratio. In this work we report the size dependence of the spin flop transition of Cr2O3 nanoparticles by magnetization measurements. The samples were synthesized from chemical precipitation followed by calcinations at different temperatures, from 1100 K to 1700 K. TGA-DTA measurements show that the Cr2O3 phase is formed completely at T 700 K. TEM measurements show that the particles have ellipsoidal shape with mean major axis of 90 nm and mean minor axis of 40 nm for the sample annealed at T = 1300 K. For this sample the spin-flop transition develops at HSF 2 T at 7 K. When the nanoparticle size increases the HSF shifts to higher magnetic field indicating that the spin-flop transition is influenced by surface effect.