Eur. Phys. J. B 52, 297-303 (2006)
https://doi.org/10.1140/epjb/e2006-00296-4

Ferromagnetic resonance in arrays of highly anisotropic nanoparticles

Centro Atómico Bariloche, Comisión Nacional de Energía Atómica, and Instituto Balseiro, Universidad Nacional de Cuyo, 8400 San Carlos de Bariloche, Río Negro, Argentina

Corresponding author: ^a butera@cab.cnea.gov.ar

Received: 20 April 2006
Revised: 26 June 2006
Published online: 31 July 2006

Abstract

We present in this study computational simulations of the ferromagnetic resonance response of magnetic nanoparticles with a uniaxial anisotropy considerably larger than the microwave excitation frequency (in field units). The particles are assumed to be randomly oriented in a two dimensional lattice, and are coupled by dipolar interactions through an effective demagnetization field, which is proportional to the packing fraction. We have included in the model fluctuations in the anisotropy field (H_K) and allowed variations in the demagnetizing field. We then analyzed the line shape and line intensity as a function of both fields. We have found that when H_K is increased the line shape changes drastically, with a structure of two lines appearing at high fields. The line intensity has a maximum when H_K equals the frequency gap and decreases considerably for larger values of the anisotropy. The effects of fluctuations in H_K and variations in the packing fraction have been also studied. Comparison with experimental data shows that the overall observed behavior is dominated by the particles with lower anisotropy.