Magnetic and Elastic Properties of CoFe2O4-PDMS Magnetically Oriented Elastomer Nanocomposites

P. SOLEDAD ANTONEL; GUILLERMO A. JORGE; OSCAR E. PEREZ; GABRIELA LEYVA; MARTÍN NEGRI

JOURNAL OF APPLIED PHYSICS

AMER INST PHYSICS

Lugar: Chicago; Año: 2011 vol. 110 p. 439201 - 439208

0021-8979

Magnetic elastic structured composites were prepared using CoFe2O4 ferromagnetic andsuperparamagnetic nanoparticles as fillers in polydimethylsiloxane (PDMS) matrixes. Cobalt-ironoxide nanoparticles of three different average sizes (between 2 and 12 nm) were synthesized andcharacterized. The smallest nanoparticles presented superparamagnetic behavior, with blockingtemperature determined by SQUID, while the largest presented ferromagnetism at room temperature.Macroscopically structured-anisotropic PDMS-CoFe2O4 composites were obtained when curing the dispersion of the nanoparticles in the presence of a uniform magnetic field (0.3 T). Formation of particle´s chains (needles) orientated in the direction of the magnetic field was observed only when loading with the ferromagnetic nanoparticles. SEM images show that the needles are formed by groups of nanoparticles which retain its original average size. The Young´s modules of the structured composites are fourth times larger when measured along the oriented needles than in the perpendicular direction.Magnetization curves (VSM) of the structured composites were determined as function of the relative orientation between the needles and the probe field. The remanent magnetization was 30% higher when measured parallel to the needles, while the coercive field remains isotropic. These observations are discussed in terms of the individual nanoparticles properties and its aggregation in the composites.