Anisotropy and relaxation processes of uniaxially oriented CoFe2O4 nanoparticles dispersed in PDMS

JORGE, G. A.; ANTONEL, P. S.; NEGRI, R. M.; LEYVA, A. G.

Buenos Aires

Congreso; At the Frontiers of Condensed Matter V; 2010

Comisión Nacional de Energía Atómica - Centro Atómico Constituyentes

When a uniaxial magnetic field is applied to a non-magnetic dispersive medium filled with magnetic nanoparticles, they auto-assemble into thin needles parallel to the field direction, due to the strong dipolar interaction among them. We have prepared in this way magnetically oriented nanocomposites of nanometer-size CoFe2O4 particles in a PDMS polymer matrix, with a 5 and 10 % w/w of magnetic particles. In this work, we present the characteristic magnetization and magnetic relaxation curves measured with the applied magnetic fields forming an angle "alpha" with respect to the needle direction. In both experiments, a small magnetic anisotropy is present. We show that the magnetic viscosity (calculated from the logarithmic relaxation curves) as a function of "alpha" presents a minimum a alpha = 0, indicating slower relaxation processes associated with this configuration of fields. The results seems to point out that the local magnetic anisotropy of the nanoparticles is oriented along the needles, resulting in the macroscopic magnetic anisotropy observed in our measurements.