Determination of the Magnetic Anisotropy Constant for Magnetic Nanoparticles Using a Debye Model

Victoria L. Calero, University of Puerto Rico, Mayaguez, PO Box 9046, Mayaguez, PR 00680 and Carlos Rinaldi, Chemical Engineering, University of Puerto Rico Mayaguez Campus, Mayaguez, PR 00680.

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.