Magnetic order in amorphous nanoparticles

DE BIASI EMILIO; ZYSLER ROBERTO; RAMOS CARLOS; ROMERO HÉCTOR

Ruinas de Quilmes, Tucumán, Argentina.

Congreso; NSF-CONICET Quilmes Workshop: Electronics with Molecules and Quantum Dots.; 2003

We present magnetization measurements on ~3 nm (Fe0.26Ni0.74)50B50 and (Co0.25Ni0.75)65B35 ferromagnetic amorphous nanoparticles. Our results show evidence of the surface contribution to the magnetic properties in the M(H) and M(T) measurements. We observe a large increase of the magnetization with decreasing temperature, a non-saturated component in the M(H) curves, the presence of two maxima 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 a uniaxial anisotropy contribution. Monte Carlo simulations based in a core-shell model qualitatively reproduce all the observed phenomena.