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Abstract
The electron excitation mechanism and the spin accompanied by electron transition in a multiferroic YMnO3 epitaxial thin film were studied using photoluminescence (PL) spectroscopy. The thin film exhibits an intra-atomic transition of Mn3+ and the A1 optical coherent phonon. This study particularly focuses on the correlation between the electron transition corresponding to the on-site Coulomb energy and antiferromagnetic spin order. To clarify the complex excitation mechanism, the excitation energy and temperature dependences of the PL were analyzed. The key finding was that the intensities of the PL band at 1.43 eV increase as the excitation energy approaches the absorption peak energy corresponding to the on-site Coulomb energy and as the temperature decreases below 80 K, corresponding to the Néel temperature. These results suggest that the PL band is mediated by the spin–flip and relaxation processes.
Highlights
Multiferroics are materials with two or more ferroic orders, such as ferroelectricity and ferromagnetism, coexisting simultaneously in the same crystal phase.1–4 In such materials, multiple ferroresponses to external fields, such as electric fields, magnetic fields, stress, electromagnetic irradiation, and their cross-correlated properties, have been reported.2,5–8 In particular, novel photo-induced properties, such as spin control by light irradiation, photovoltaic power above the bandgap, and quantum mechanical photo-induced current, have attracted much attention in recent years.8–10 Rare-earth manganite (RMnO3; R = Ho, Er, Tm, Yb, Lu, or Y) compounds are both ferroelectric and antiferromagnetic
Using this high-quality epitaxial thin film that has almost the same crystallinity and optical absorption behavior as those of single crystals, our group found an intra-atomic transition of Mn3+ and the optical A1 coherent phonon, which originated via the electron transition related to the Mn 3d orbital, despite scitation.org/journal/adv scitation.org/journal/adv the influence of the epitaxial strain
We have shown the excitation energy dependence of the PL measured at 10 K using a YMO epitaxial thin film to discuss the electron and spin dynamics that accompany electron transitions, especially those corresponding to the absorption peak originating from the Mn 3d orbitals
Summary
The magnetic and lattice vibrations in the hexagonal YMO show anomalous behavior around the antiferromagnetic phase transition and are related to electron transition, especially to the on-site Coulomb energy. This PL band is highly correlated with the antiferromagnetic transition that occurs at TN = ∼80 K, suggesting that carrier dynamics are related to the antiferromagnetic transitions in YMO These PL measurements are done at excitation energies of 2.41 and 2.54 eV, which are different from the on-site Coulomb energy corresponding to absorption peak energy at 1.8 eV in YMO. This paper discusses the excitation mechanism of the electron and spin accompanied by electron transition, especially corresponding to the on-site Coulomb energy originating from the Mn 3d orbital
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