(164q) Determination of the Magnetic Anisotropy Constant for Magnetic Nanoparticles Using a Debye Model

Magnetic ferrite nanoparticles were synthesized using reverse micelles, obtaining highly monodisperse nanoparticles with approximately ~3 nm diameter and a geometric deviation of ~0.2. The particles were characterized magnetically using a SQUID magnetometer with an AC susceptometer. The Debye model for a magnetic dipole in an oscillating field was used to determine the anisotropy constant from AC susceptibility measurements. Assuming magnetic relaxation proceeds through the Néel mechanism, a relation between χ' and the temperature of the AC in-phase susceptibility curve peak was obtained. Using this relation, anisotropy constant values in the order of ~10⁶ kerg/cm³ were determined, whereas anisotropy constants in the order of ~10⁷ kerg/cm³ were calculated assuming Ωτ=1 at the temperature peak of the in-phase component of the susceptibility curve.