Surfaces and local anisotropy effect in the magnetic order of Fe-Co-B nanoparticles

3 nm (Fe(x)Co(1-x))(y)B(1-y), (0 less than or equal to x less than or equal to 1, y approximate to 0.6) nanoparticles were synthesized by chemical route. XDR and TEM measurement show the amorphous nature of the samples. Size distribution was characterized by light-scattering measurement. Magnetization vs. magnetic field measurements at room temperature show hysteresis loop for all compositions, typical of blocked single domains. In powder samples, room temperature coercive field and remanent are larger for Fe- or Co-rich composition, and saturation magnetization exhibit a minimum at x = 0.15. This behaviour is related to the composition of the different local anisotropy associated to Fe and Co ions. (C) 2004 Published by Elsevier B.V.