Effects of superparamagnetic relaxation in nuclear small-angle scattering of synchrotron radiation

The effects of superparamagnetic relaxation are simulated for nuclear resonance small-an-le scattering of synchrotron radiation from an ensemble of magnetic nanoparticles. The theoretical formalism based on the Maxwell-Neumann quantum equations is used to describe the resonant interaction of the incident gamma quanta and Mossbauer atoms in a small-angle scattering channel in the presence of equilibrium fluctuations of the local magnetization of nanoclusters. The evolution of the resonant response of uniaxial magnetic particles is analyzed as a function of the fluctuation frequency (superparamagnetic relaxation rate), the probabilities of formation of the directions of local magnetization, and the external magnetic field. The analysis of this evolution allowed us to develop an additional method for nondestructive control of the stability of magnetic properties possessed by an ensemble of nanoparticles. (C) 2004 MAIK "Nauka/Interperiodica".