1. University of Oviedo,Department of Physics & IUTA,Asturias,Spain
2. Institute of Structure of Matter-National Research Council (CNR),Rome,Italy
3. Romanian Academy-Timisoara Branch, Center for Fundamental and Advanced Technical Research,Laboratory for Magnetic Fluids,Timisoara,Romania
4. Università degli Studi di Genova,Department of Chemistry and Industrial Chemistry,Genova,Italy