Internal magnetic structure in amorphous nanoparticles of Fe-Nd-B

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

Rome, Italy

Conferencia; 6th International Conference on Fine Particle Magnetism (ICFPM07), New trends in nanoparticle magnetism; 2007

The internal magnetic order in amorphous nanoparticles of (FexNd1-x)0.6B0.4 (x = 0.25, 0.5, 0.85) has been studied. These nanoparticles were dispersed in a non-magnetic matrix in order to prevent interparticle interactions. The different Nd amount in the composition affects the internal magnetic order of these nanoparticles by weakening the exchange interactions. The magnetic order in the particles has been described in the frame of the core–shell model, i.e., an ordered ferromagnetic core and a disordered paramagnetic surface. The temperature behaviour of the spins in the shell is very dependent of Nd content: for lower Nd concentration the surface order is governed by ferromagnetic exchange interactions, and for the higher one the disordered shell remains paramagnetic in the whole measured temperature range without showing evidences of a growing ferromagnetic order. On the other hand, coercive field measurements denote the presence of two anisotropies, i.e., the core one, which dominates at high temperatures and the surface one, which dominates at low temperatures and is responsible of the evident frustration present in the magnetisation of the surface spins. This is in complete agreement with previous works which show that the Nd atoms break the exchange paths and rises the anisotropy, as we could see in our coercive field measurements [1-4].   [1] M. Sagawa et al. J.Appl.Phys. 55, (1984) 2083.[2] Akira Fukuno and R. C. O´Handley. J.Appl.Phys. 65, (1989) 4959.[3] Akira Fukuno and R. C. O´Handley. IEEE Transactions on Magnetics 26, (1190) 250.[4] M. Tortarolo, R.D. Zysler, H. Troiani, H. Romero, Physica B 354, (2004) 117.