Probing the Phase Separation in the Doped Manganites by the Magnetic Resonance Methods

Here we present magnetic resonance study which confirms an existence of a phase separation picture in Eu$\text{}_{0.7}$Pb$\text{}_{0.3}$MnO$\text{}_{3}$ single crystals. The measurements were performed with a standard technique and with using unconventional schemes of the magnetic resonance method. The inhomogeneous paramagnetic-ferromagnetic state, which is sensitive to a magnetic field, takes place in 0.65T$\text{}_{c}$-1.15T$\text{}_{c}$ temperature range, where the colossal magnetoresistance effect is observed. The behavior of spectra suggests that a scenario of the phase separation is realized and the mixed state is not related to a simple chemical inhomogeneity. The changes of the conductivity induced by the microwave resonance absorption are observed in a vicinity of T$\text{}_{c}$, too. The changes are not related to a trivial heating of the sample by a microwave radiation. We propose a mechanism connected with the change of equilibrium concentrations of the coexisting phases, this change takes place when the system is under magnetic resonance conditions. To analyze the experimental data we applied the effective-medium approximation for two-component system. Also we attracted the simplest phenomenological model qualitatively reproducing the essential features of the behavior of the two-phase system.