https://doi.org/10.1140/epjb/e2008-00122-1
Uniform spin wave modes in antiferromagnetic nanoparticles with uncompensated moments
1
Materials Research Department, Risø DTU, 4000 Roskilde, Denmark
2
Fuel Cells and Solid State Chemistry Department, Risø DTU, 4000 Roskilde, Denmark
3
DTU Physics, Bldg. 307, Technical University of Denmark, 2800 Kongens Lyngby, Denmark
4
Niels Bohr Institute, University of Copenhagen, 2100 København Ø, Denmark
Corresponding author: a christian.bahl@risoe.dk
Received:
13
December
2007
Revised:
20
February
2008
Published online:
21
March
2008
In magnetic nanoparticles the uniform precession (q = 0 spin wave) mode gives the predominant contribution to the magnetic excitations. We have calculated the energy of the uniform mode in antiferromagnetic nanoparticles with uncompensated magnetic moments, using the coherent potential approximation. In the presence of uncompensated moments, an antiferromagnetic nanoparticle must be considered as a kind of a ferrimagnet. Two magnetic anisotropy terms are considered, a planar term confining the spins to the basal plane, and an axial term determining an easy axis in this plane. Excitation energies are calculated for various combinations of these two anisotropy terms, ranging from the simple uniaxial case to the planar case with a strong out-of-plane anisotropy. In the simple uniaxial case, the uncompensated moment has a large influence on the excitation energy, but in the planar case it is much less important. The calculations explain recent neutron scattering measurements on nanoparticles of antiferromagnetic α-Fe2O3 and NiO.
PACS: 76.50.+g – Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance / 75.75.+a – Magnetic properties of nanostructures / 75.50.Ee – Antiferromagnetics / 75.30.Gw – Magnetic anisotropy
© EDP Sciences, Società Italiana di Fisica, Springer-Verlag, 2008