ORIENTATIONAL DEGREE OF MAGNETIC NANOPARTICLES EMBEDEED IN CONDUCTING POLYMERS; 

D. Toloman1, M.N. Grecu2, I. Craciunescu1, X. Filip1, O. Raita1, R. Turcu1 and L.M.Giurgiu1 

1National Institute for Research and  Development of Isotopic and Molecular Technologies, P.O. Box 700, R-400293, Cluj-Napoca,Romania
2National Institute for Material Physics, 76900 Bucharest - Magurele, P.O.Box MG-7, Romania

Conducting polymer nanocomposites based on polypyrrole (PPY) and -Fe2O3 magnetic particles have been investigated by means of EPR measurements. 
	The EPR spectra for the investigated samples show two resonance lines: a narrow line and a broad one that could be attributed to the paramagnetic PPY matrix and the superparamagnetic -Fe2O3 nanoparticles, respectively [1]. The line shape for the broad line was found to be Lorentzian independently of the particle size. From the corresponding fit, the linewidth, H1/2, and the resonance field, H0, were evaluated as function of temperature in the temperature range 80-300 K [2].
	A phenomenological model for changes in H1/2 and H0 in magnetic nanoparticles with decreases in temperature was used to interpret our data. The model predicts 
H0 = ( H1/2 )n , where n = 2 for partially oriented and n = 3 for randomly oriented magnetic particles [3]. Here, H0, is the shift of the resonance field with respect to that appropriate to the bulk material. Using the resonance field corresponding to bulk -Fe2O3 particles and the temperature dependencies of H1/2 and H0, a value of n = 2.28 could be evaluated. It could means that the antiferomagnetic nanoparticles -Fe2O3 are partially oriented in PPY matrix.

[1] R.Turcu, I.Peter, O.Pana, L.M.Giurgiu , N.Aldea, B.Barz, M.N.Grecu, I.Chicinas, A.Coldea: Molec. Cryst.  & Liq. Cryst. 415, 189 (2004)
[2] D. Toloman, M.N. Grecu, I. Craciunescu, X. Filip, I. Ardelean, R. Turcu and L.M. Giurgiu: Procc. “21-th International RAMIS Conference on Radio and Microwave Spectroscopy”, Poznan, Poland, Ed. S. Waplak, p45 (2005)
[3]. K. Nagata, A. Ishihara, J.Magn.Magn. Mat. 104-107, 1571 (1992)