Magnetic order in amorphous nanoparticle system

E. DE BIASI; ZYSLER ROBERTO; RAMOS CARLOS; ROMERO HÉCTOR; FIORANI DINO

San Carlos de Bariloche, Argentina

Congreso; Pan American Advanced Studies Institute on Physics at Nanometer Scale; 2003

We present magnetization on ~3nm (Fe0,26Ni0,74)50B50 and (Co0,25Ni0,75)65B35 nanoparticles syntethysed by chemical route, with an narrow size distribution. These systems were dispersed in a non-magnetic polymer matrix so that the interparticle interactions could be neglected. Our results show evidence of the surface contribution to the magnetic properties in the M(H), M(T) and relaxation measurements. In relation with this effect we observe a large increase of the magnetization with decreasing temperature, a non-saturated component in the M(H) curves, the presence of two mamxima in the zero field cooling M(T) data. The results has been interpreted by a simple model where we consider each single-domain particle as a system of exchange-coupled classical spins in presence of an applied magnetic field  with an uniaxial anisotropy contribution. Monte Carlo simulations based in a core-shell model qualitativaly reproduce all the observed phenomena.