Characterization of a Ferrogel of iron oxide magnetic nanoparticles in a PVA network

L. ARCINIEGAS; P. MENDOZA ZÉLIS; G. A. PASQUEVICH; J. S. GONZALEZ; C. HOPPE; V. A. ALVAREZ; F. H. SÁNCHEZ

Buenos Aires

Workshop; VII Latin American Workshop on Magnetism, Magnetic Materials and their applications; 2013

Ferrogels (FGs) are nanocompounds made of magnetic nanoparticles (NPs) dispersed in a polymeric network (hydrogel). They found applications in artificial muscles and magnetically modulated drug administration. In this communication a study of the magnetic properties of polyvinyl alcohol (PVA)/iron oxide nanoparticles ferrogels synthetized by freezing-thawing method, is presented. M vs H cycles were recorded at RT in a VSM. Susceptometry studies were done between 14 K and 300 K at 825 Hz. Finally M vs H cycles were measured at different temperatures from 10 K to 290 K, and FC-ZFC magnetization was recorded in the same temperature range under 4 kA/m and 8 kA/m fields in a SQUID. ZFC measurements showed an average temperature maximum of 17-25 K. From analysis, we obtained a characteristic NP diameter D between 4.9 - 5.6 nm. The analysis of M vs H curves at all temperatures presents a systematic inconsistency: the NP moment seems to increase linearly with temperature. This type of behavior was attributed to an effect of dipolar interactions among particles. TEM observations indicate a homogeneous distribution of NPs with a mean distance between them d ≥ 3D, therefore suggesting no important dipolar effects. The observed behavior of saturation magnetization Ms vs T gives an evidence of moment collective oscillations leading to M s(T ) = M s(0)(1 − αT ), where α = kB B , being kB the Boltzmann constant, K the NPs magnetic effective KV anisotropy constant, and V the NPs mean volume. Possible origins of the nonphysical NPs apparent moment temperature behavior will be discussed.