Ferromagnetic resonance in ferrofluids.

H. M. Sauer

SusTech GmbH, Petersenstrasse 20, D-64287 Darmstadt

Abstract
Ferrofluids and suspensions of isolated magnetic nanoparticles in non-magnetic hosts show rich microwave absorption spectra with several clearly distinct resonance lines, which correspond to ferromagnetic resonance (FMR) and the long-wavelength spin wave excitations in individual particles. The positions and widths of the resonance lines reveal important information on the magnetic ordering in the ferrofluid on the nanometer scale: the magnetic bulk and surface anisotropy energy, the intra-particle exchange interaction, the particle size distribution, and the static quadrupolar moments of the particles. As an example, the FMR spectrum of a magnetite based ferrofluid is considered. Figs 2, Refs 6.