Study on Photo-induced Phenomena in Strongly Correlated Ferroelectric YMnO_3 Thin Films

概要

1-1 Research Background
Strongly correlated electron systems, which are found in transition-metal
compounds, exhibit novel and interesting properties, including superconductivity,
topological properties, and quantum liquids, due to the strong spin-electron-orbit
interaction; these properties cannot be explained by conventional band theory. Among
strongly correlated systems, multiferroic materials are those materials in which several
ordered phases such as magnetic and ferroelectric orders coexist in the same crystal, and
the development of multiferroic materials has been actively investigated [1-3]. These
materials exhibit novel properties, such as multiple ferroic responses to external fields,
including the electric field, magnetic field, stress, and light.
Multiferroic materials with both of ferroelectric and magnetic orders were
predicted by Pierre Curie et al., at the end of the 19th century. Multiferroic materials have
attracted interest since the discovery of colossal electromagnetic effects in perovskitetype rare-earth manganite TbMnO3 in 2003 [4]. TbMnO3 exhibits ferroelectricity-induced
cycloidal spiral spin order [5,6]. Under the application of a magnetic field, TbMnO3
exhibits a spin-flip transition, where the polarization vector rotates by 90°. The correlation
between the cycloidal-spiral spin structure and ferroelectric polarization is thought to be
associated with the Dzyaloshinskii–Moriya interaction [7]. A magnetic field induced
polarization flop has been reported in some materials with RMn2O5, MnWO4, LiCu2O2,
and CoCr2O4 [8-11]. ...

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