Magnetic surface order in amorphous (Fe0.25Nd0.75)0.6B0.4

M. TORTAROLO; R. D. ZYSLER; H. ROMERO

San Carlos de Bariloche

Workshop; 13th International Conference on Solid Films and Surfaces; 2006

Centro Atómico Bariloche, CNEA

We present a magnetic characterisation or (Fe0.25Nd0.75)0.6B0.4 nanoparticles of » 7 mn diameter. Surface effects are enhanced in this compounds because of the high surface – volume ratio (40 %) and due to the low Fe content that softens the ferromagnetic coupling and makes the order grow gradually.  We studied dispersed nanoparticles in a non- magnetic matrix (weakly interacting system) as well as in powder samples (interacting system) in order to understand both the influence of the internal structure and the interactions among particles. The experimental characterisation of the saturation magnetisation shows a sharp increase below 60 K which evidences the presence of surface anisotropy, stronger at low temperatures. Coercive field follows the magnetic moment tendency confirming that the anisotropy is mainly due to the shape of the particles(1). We discus these results in the frame of a core-shell model which represents each particle as an ordered core plus an initially disordered shell that grows ordered as the temperature is lowered. Interparticle interaction effects in the magnetic order are also discussed.