Phase separation and charge carrier self-organization in semiconductor-multiferroicEu0.8Ce0.2Mn2O5

Abstract

The state with a giant permittivity ͑Ј ϳ 10 4 ͒ and ferromagnetism have been observed above 185 K ͑including room temperature͒ in single crystals of diluted semiconductor manganite-multiferroic Eu 0.8 Ce 0.2 Mn 2 O 5 in the investigations of x-ray diffraction, heat capacity, dielectric and magnetic properties, conductivity, and Raman light-scattering spectra of this material. X-ray diffraction study has revealed a layered superstructure along the c axis at room temperature. A model of the state with a giant Ј including as-grown two-dimensional layers with doping impurities, charge carriers, and double-exchange-coupled Mn 3+-Mn 4+ ion pairs is suggested. At low temperatures these layers form isolated electrically neutral small-size one-dimensional superlattices, in which de Haas-van Alphen oscillations were observed. As temperature grows and hopping conductivity increases, the charge carrier self-organization in the crystal causes formation of a layered superstructure consisting of charged layers ͑with an excess Mn 3+ concentration͒ alternating with dielectric layers of the initial crystal-the ferroelectricity due to charge-ordering state. Ferromagnetism results from double exchange between Mn 3+ and Mn 4+ ions by means of charge carriers in the charged layers. Temperature evolution of frequency shifts of A g modes and quasielastic scattering in Raman-scattering spectra agree with the pattern of phase transitions in ECMO suggested.

Spin-wave resonances in Eu0.8Ce0.2Mn2O5 and EuMn2O5 multiferroics

“…These regions are aligned in front of each other along the c axis, forming one dimensional (1D) superlattices. Such a phase separa tion pattern in ECMO related to the EMO layered structure was found by high precision X ray diffrac tion studies [1,2]. At room temperature, the period of the superstructure along the c axis equals ≈700-900 Å [1,2].…”

“…These results were compared with those for EuMn 2 O 5 (EMO). Both ECMO and EMO have the same symmetry at room temperature (Pbma space group) and unit cell parameters close to each other [1]. The specific heat studies for ECMO demonstrate that it exhibits the same series of low temperature phase transitions as EMO.…”

“…The specific heat studies for ECMO demonstrate that it exhibits the same series of low temperature phase transitions as EMO. This implies that the volume in ECMO modified by the doping is small in this temper ature range [1].…”

“…In [1,2], we presented the results concerning the dielectric, magnetic, and structural characteristics of Eu 0.8 Ce 0.2 Mn 2 O 5 (ECMO) semiconductor-multifer roic. These results were compared with those for EuMn 2 O 5 (EMO).…”

Магнитная динамика областей фазового расслоения в мультиферроиках GdMn-=SUB=-2-=/SUB=-O-=SUB=-5-=/SUB=- и Gd-=SUB=-0.8-=/SUB=-Ce-=SUB=-0.2-=/SUB=-Mn-=SUB=-2-=/SUB=-O-=SUB=-5-=/SUB=-

“…В последующих работах было показано, что области фазового расслоения возника-ют и в других кристаллах, содержащих ионы разной валентности. При этом форма этих областей зависит от соотношения величин взаимодействий, формирующих эти области, и может иметь вид как 2D плоских, так и 1D образований [12][13][14][15][16].…”