The electron-paramagnetic resonance linewidth of double-exchange interaction systems

We studied the electron-paramagnetic resonance linewidth of colossal magnetoresistance manganites. Starting from the quantum Langevin equation, we derived the transverse susceptibility of the double-exchange interaction systems and identified the damping function to be the inverse of the relaxation time T-2. We argued that the anisotropic energy caused by the crystal field was the most probable relaxation mechanism. The spin correlation caused by the double-exchange interaction was examined with the Schwinger boson approach. Taking into account the constraints of Schwinger bosons, we found that the linewidth is approximately proportional to the temperature. At the low-temperature end (near the Curie temperature T-C), there is a minimum, below which the linewidth increases sharply. At the high-temperature limit, the linewidth is proportional to rootT/T-C. Most importantly, the linewidth is a universal function of T/T-C.