Eur. Phys. J. D 52, 19-22 (2009)
https://doi.org/10.1140/epjd/e2008-00283-y

Implications of nanoparticle concentration and size distribution in the superparamagnetic behaviour of aging-improved maghemite xerogels

¹ Departamento de Física de la Materia Condensada, Facultad de Ciencias, Universidad de Cádiz, Campus Universitario de Puerto Real, 11510 Puerto Real, Spain
² Fisika Aplikatua II saila, Zientzia eta Teknologia Fakultatea, Euskal Herriko Unibertsitatea (UPV/EHU), 644 P.K., 48080 Bilbao, Spain

Corresponding author: ^a daniel.ortega@uca.es

Received: 19 September 2008
Published online: 24 January 2009

Abstract

Evolution of static magnetic properties of a set of enhanced γ-Fe₂O₃/SiO₂ nanocomposites with different iron concentration has been studied on the basis of their corresponding hysteresis loops, zero-field/field-cooled (ZFC/FC) magnetization curves and transmission electron microscopy images. The lack of coercivity in all compositions, as well as the fulfillment of the H/T scaling law by the magnetization above the blocking temperature of each system under study, evidence a superparamagnetic behaviour in the iron oxide nanoparticles. In order to study the influence of iron content in the unblocking processes of nanoparticles, ZFC curves under different applied magnetic fields have been fitted to a model considering the systems under study as a distribution of energy barriers. Depart from the superparamagnetic model is discussed considering interparticle interactions.