Size effects and interparticle interactions in the Ferromagnetic Resonance (FMR) spectroscopy - new approaches to investigate dispersed magnets and catalytic systems based on it
Dr. O. Martyanov (Boreskov-Institut für Katalyse, Nowosibirsk, Russland)

Abstract:
An original approach is proposed to study the dipole-dipole interparticle interactions in dispersed magnets. It is the registration and analysis of so called noise like Ferromagnetic Resonance Fine Struc-ture (FMR FS), which is caused by the magnetic dipole-dipole interaction between magnetic domains. The features of the Fine Structure formation are discussed. Some experimental examples of the possible applications of the FMR FS method are given. It is shown that the analysis of the Fine Structure in man-ganite single crystals can be an original tool to study the magnetic phase separation phenomenon.
The fundamental role of the magnetic dipole-dipole coupling in Ferromagnetic Resonance is demon-strated with an example of collective phenomena in two-dimensional periodic arrays of disk-shaped Co particles. A study of geometrically similar structures with different periods reveals a broadening of the FMR resonance lines due to the excitation of additional size-dependent non-uniform spin waves. It is shown that these collective spin-wave modes are based on dipole–dipole interactions between the ferro-magnetic particles in the array. Qualitative and quantitative data on magnetic interparticle interactions can thus be obtained from FMR spectra for two-dimensional periodic arrays of ferromagnetic particles.
It’s shown that approaches based on the size effects in ferromagnetic resonance developed in the controlled atmosphere in-situ conditions allow to get so far inaccessible information on early stage of the active catalysts phase formation and its structure peculiarities. In particular the investigations of sup-ported bimetallic catalyst based on Pd, Co, Fe, Ni revealed that the deposition of Pd on top of Co or Fe particles lead to more than 100% growth of the particle magnetic moment that is caused by structural rearrangements within the Co particles.
In conclusion it is shown that the size effects and interparticle interactions in the FMR spectroscopy give new opportunities to investigate magnetic nanoparticles and the systems based on dispersed mag-nets.