Superparamagnetic resonance of single-domain nanoparticles of LaSrMnO3

The microwave absorption of an ensemble of single-domain nanoparticles of La0.7Sr0.3MnO3 is investigated in the temperature range 5-300 K. At low temperatures the resonance spectra demonstrate the appreciable increase in linewidth and downward shift of the resonance field which are typical for superparamagnetic resonance. With increasing temperature the line shape changes, and at T > T-B (T-B similar to 100 K) one observes a narrowing of the resonance curve and saturation of the resonance field. The line shape of an individual nanoparticle is described by the dynamic Landau-Lifshitz equations with damping. Modeling of the magnetic dynamics of the system is based on the assumption of a random distribution of the directions of the magnetic moments and of the thermal fluctuations of the direction of the anisotropy axis of the particles. The theory takes into account the dependence of the value of the resonance field on the linewidth. (c) 2007 American Institute of Physics.