Probing the phase separation in the doped manganites by the magnetic resonance methods

Nikita V. Volkov 1Guerman A. Petrakovskii Klara A. Sablina 

1. L.V.Kirensky Institute of Physics Siberian Branch of the Russian Academy of Science (IPH SB RAS), Academgorodok, 50, Krasnoyarsk 660036, Russian Federation

Abstract

Here we present the magnetic resonance studies which confirm the existance of the phase separation picture in the Eu0.7Pb0.3MnO3 and La0.7Pb0.3MnO3 single crystals. These studies demonstrate that the magnetic resonance method is an effective tool for probing inhomogeneous states in the manganites. The measurements were performed with a conventional technique and with using unconventional schemes of the magnetic resonance method: a spectrometer operating in a wide frequency range with a pulsed external magnetic field; a spectrometer with combined influence of the microwave irradiation and dc current. The magnetic resonance studies display the coexistence of two absorption lines in spectra, which are related to different regions in the samples. The inhomogeneous state takes place in 0.65TC - 1.15TC temperature range, where the CMR effect is observed. Studying the microwave frequency dependence of the spectra is the main feature of our investigation. This method is very powerful for the determination of the magnetic state of the coexisting phases. The frequency-field dependencies of the spectra allow to conclude that these phases are paramagnetic (PM) and ferromagnetic (FM) ones. Moreover studying of the frequency dependences is found to be an effective tool for probing the sensitivity of the mixed-phase state to the magnetic field. The behavior of the spectra suggests that there takes place the scenario of the phase separation and the mixed state is not related to the simple chemical inhomogeneity. The changes of the conductivity induced by the microwave resonance absorption are observed in a vicinity of TC, where inhomogeneous PM-FM state is the ground state for the sample. The changes are not related to a trivial heating of the sample by the microwave radiation. We propose the mechanism connected with the change of equilibrium concentrations of the coexisting phases, this change takes place when the system is under magnetic resonance conditions.

Presentation: invited oral at E-MRS Fall Meeting 2003, Symposium D, by Nikita V. Volkov
See On-line Journal of E-MRS Fall Meeting 2003

Submitted: 2003-04-29 04:10
Revised:   2009-06-08 12:55
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