Europhys. Lett, 47 (1), pp. 122-127 (1999)
Dynamical properties of non-interacting Co nanoparticles
M. Respaud 1, M. Goiran 1, J. M. Broto 1, F. Lionti 2, L.
Thomas 2, B. Barbara 2
T. Ould Ely 3, C. Amiens 3 and B. Chaudret 3
1 LPMC-SNCMP, Insa, Complexe Scientifique de Rangueil
31077 Toulouse Cedex, France
2 Laboratoire Louis Néel - 25 avenue des Martyrs, 38042 Grenoble Cedex, France
3 Laboratoire de Chimie de Coordination
205 route de Narbonne, 31077 Toulouse Cedex, France
(received 4 December 1998; accepted in final form 20 April 1999)
PACS. 75.50Tt - Fine-particle systems.
PACS. 76.60Es - Relaxation effects.
The dynamical properties of the magnetic moment of non-interacting
cobalt nanoparticles dispersed in a polymer were investigated by ac-susceptibility
(). We thus estimated the relaxation time of the magnetisation
() associated to the superparamagnetic properties of the particles. was
found to follow
the general Néel-Brown relaxation dynamics, with a pre-exponential relaxation time of for temperatures between 10 and 20 K. By combining the experimental results from ferromagnetic resonance, ac-susceptibility, and magnetisation, measurements giving the microscopic and macroscopic parameters, we demonstrate for the first time that the Coffey theoretical expressions were able to predict both and values. Finally, the thermal dependence of is discussed.
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