PROPRIEDADES ESTRUTURAIS, VIBRACIONAIS E ELÉTRICAS DAS MANGANITAS ORTORRÔMBICA EuMnO3 e HEXAGONAL ErMnO3

Abstract

We investigated the structural, magnetic and vibrational properties of orthorhombic EuMnO3 and hexagonal ErMnO3 manganites using X-Ray Diffraction (XRD), Magnetometry, Raman spectroscopy and Dielectric spectroscopy. The structural and vibrational data obtained respectively via X-ray and Raman diffraction are consistent with the Pnma space group orthorhombic symmetries (D2h 16 -62) and the P63cm space group hexagonal symmetries (C6υ 3 -185)) for the EuMnO3 and ErMnO3 manganites, respectively. X-ray diffraction data as a function of temperature for both manganites show that there are deviations in the monatomic behavior of both lattice parameters and interatomic distances, unprecedented information for both manganites, since structural data as a function of temperature are scarce for these manganites, which allowed us to analyze in more detail the cause of the strong renormalizations of phonon frequencies and evidence of isostructural transitions. In addition, our XRD results for the EuMnO3 manganite give indications of the orbital ordering of the lattice associated with the Jahn-Teller distortion and we also observed, from the structural data, behaviors consistent with the magnetic ordering of the Mn spins in the ac plane, a result that is very interesting since the literature reports difficulty in obtaining the orientation of the spins for EuMnO3. Regarding the ErMnO3 manganite, we observed evidence of the participation of the Mn3+ (site 6c) and Er3+ (site 4b) spin networks, contrary to what is reported for the hexagonal manganites ReMnO3 (Re = Y, Dy, Ho, Tm, Yb and Lu) that indicate only the participation of the spin network of Mn3+ (site 6c) for the magnetic symmetry. In addition, we observed evidence of the occurrence of isostructural transitions involving the Er3+ spin network occurring from the Γ2 Er configuration to the Γ4 Er . The dielectric measurements data for the polycrystalline ErMnO3 manganite allowed us to investigate in more detail the contributions of grains and grain boundaries to the electrical conductivity, important results since the few existing results in the literature are concentrated in monocrystalline samples. In addition, the dielectric measurements showed anomalies in the dielectric constant in the vicinity of the magnetic region, these anomalies, together with magnetometry results, suggest the existence of magnetoelectric coupling for ErMnO3. Finally, we show evidence of a coupling between multi-order parameters and their interaction with the magnetoelectric effect in h-ErMnO3. A high magnetostriction response is evidenced by the Einstein-Grüneisen model.