Effect of coating and dispersion on the interparticle magnetic interactions between 3 nm -Fe2O3 nanoparticles

I. O. PEREZ DE BERTI; J.F. BENGOA; G.A. PECCHI; J.L. ALESSANDRINI; S.G. MARCHETTI; S.J. STEWART

Buenos aires

Workshop; Latin American Workshop on Magnetism, Magnetic Materials and their Applications; 2013

To explore dierent ways of controlling and reducing the magnetic interaction strength between monodispersed particles of small average size, we present an investigation on -Fe2O3 nanoparticles showing these features. To this aim, -Fe2O3 nanoparticles were synthesized by a thermal decomposition of organometallic iron salts in an organic solvent with a high boiling point, in presence of a surfactant (oleic acid). The as-synthesized particles present an average size of 2.5(6) nm determined by transmission electron microscopy (TEM) and dynamic light scattering (DLS), and are coated by a monolayer of oleic acid as observed by FT-IR. This coating preserves particle contact and establishes a minimum distance between particle moments of about 2 nm. The superparamagnetic to blocked state transition of -Fe2O3 particle moments were followed by Mossbauer spectroscopy (MS) in the 12 to 298 K range and magnetic measurements. The latter showed a blocking temperature at about TB= 17 K under an applied eld of 50 Oe. To alter the strength of magnetic interactions, the -Fe2O3 nanoparticles were embedded in a mesoporous material SBA- 15 with an average porous diameter of 11 nm. TEM results indicate that after impregnation the particles are distributed inside the porous without agglomeration. The MS results show that the iron species is preserved after the dispersion inside the matrix. Magnetic and MS results show that the rate of the progressive blocking of moments, as well as the blocking temperature of -Fe2O3 remain unaected after being hosted in SBA-15. We conclude that the initial coating of 2 nm is enough to weaken the exchange interparticle interactions and the moments behaves independently.