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   붙임2_응용물리학과 세미나 공고문(181011최우석교수).pdf (205.3K) [4] DATE : 2018-10-11 17:00:08
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2018.10.11 (수) 콜로키움 공지입니다.
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◎ 연사: 성균관대학교 물리학과 최우석 교수
◎ 제목:Coupled Ferroelectricity and Ferromagnetism in 1D Tetrahedral Chain Network via Combined Polar Distortion
◎ 초록: Recent advances in engineering transition metal-oxygen (TMO) octahedra led to a fundamental understanding on the functionalities emerging at transition metal oxides. Unconventional ferroelectricity can also emerge as a consequence of a collective distortion of TMO6 octahedra in two dimensional networks. In the meantime, TMOx polyhedra with different oxygen coordinate, such as TMO4 tetrahedra with a lower structural symmetry can also form a low dimensional network and can exhibit intuitive inversion symmetry breaking through a collective distortion. In this talk, we focus on brownmillerite strontium ferrite SrFeO2.5 (SFO). The brownmillerite structure possesses one-dimensionally ordered oxygen vacancy channels, which can equivalently be viewed as a one-dimensional chain of FeO4 tetrahedra. Furthermore, a collective rotation of the FeO4 tetrahedra, or a combined polar distortion, can break the structural inversion symmetry, which can be observed from the imaginary phonon dispersion at both zone-center and zone-boundary. The ferroelectricity expected in 1D tetrahedral network, is experimentally validated by second harmonic generation, piezoforce microscopy, and switching current measurements. Based on the inversion symmetry, possible correlation to the magnetic ordering will be also discussed.