Studies of manganites by magnetic resonance spectroscopy methods

Abstract

In this work, we present the studies of manganites with superfluous manganese content performed by the magnetic resonance spectroscopy methods. The ferromagnetic resonance (FMR) has been measured on the films. The symmetrical FMR line in paramagnetic phase has the Dysonian-like shape below Tc. The FMR linewidth increases abruptly near the transition temperature. By comparing resonance fields oriented parallel and perpendicular to the film plane, the easy axis of magnetization was determined to be perpendicular to the film plane. In the perpendicular magnetic field, the spin-wave resonance (SWR) spectrum consisting of seventeenth of spin-wave modes has been observed in the (formula available in paper) film. Two of them observed on the high-field side of SWR spectrum are connected to a surface modes. The others are the bulk nonuniform spin-wave modes. Based on a study of temperature and angular dependencies of SWR and FMR spectra, the spin- wave stiffness, g-factor and exchange constant were established. An analysis of the (formula available in paper)has shown that a wide asymmetrical line can be uniquely expanded into four components with different resonance frequencies. There are manganese ions, which ionization states are close to (3+) and (4+) as well as the Mn ions with intermediate valence resulted from the high-frequency electron exchange.