Title page for etd-0018117-174238


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URN etd-0018117-174238
Author Hung-Cheng Wu
Author's Email Address hungcheng.wu@gmail.com
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Department International PhD Program for Synchrotron Radiation and Neutron Beam Applications
Year 2016
Semester 1
Degree Ph.D.
Type of Document
Language English
Title Novel properties in spin-frustrated systems Cu2OSeO3, Cu2OCl2, and Cu3Bi(SeO3)2O2Cl
Date of Defense 2017-01-16
Page Count 126
Keyword
  • spin-flip
  • multiferroics
  • Jahn-Teller effect
  • split
  • Skyrmion phase
  • Kagome
  • pyrochlore
  • Abstract The purpose of this dissertation is to study three geometrical spin-frustrated systems, such as the corner-sharing of tetrahedron in Cu2OSeO3, pyrochlore structure in Cu2OCl2, and Kagome lattice in Cu3Bi(SeO3)2O2Cl.
    Novel skyrmion phase in Cu2OSeO3 is a remarkable characteristic as a vortex-like spin configuration in specific magnetic field and temperature region. Using the effects of compression pressure, chemical expansion, non-magnetic (Zn) and magnetic (Ni) element doping on Cu2OSeO3, outstanding and interesting research findings were investigated. The skyrmion phase region becomes split upon Zn doping concentration. Large enhancement of skyrmion area upon Ni-doped could be ascribed to the magnetic anisotropy of the Jahn-Teller active Ni2+ ion in Cu(I) site. Under the external pressure, the skyrmion zone is enlarged owing to the enhancement of strengths of competing Dzyaloshinsky–Moriya (DM) and Heisenberg exchange (J) interactions. Skyrmion zone is gradually suppressed with Te doping, which could be related to the decrease of D/J parameter.
    Temperature and magnetic field dependent magnetization, specific heat, dielectric, and polarization properties in pyrochlore Cu2OCl2 and Kagome single crystal Cu3Bi(SeO3)2O2Cl were established as new type-II multiferroics. The mechanism of multiferroic behavior in Cu2OCl2 is related to the inverse Dzyaloshinskii–Moriya (DM) interaction. Furthermore, the key mechanism of the anisotropic spin-flip induced multiferroicity in Cu3Bi(SeO3)2O2Cl can be ascribed to the breaking of magnetic two-fold symmetry in the bc plance above Hc.
    Advisory Committee
  • Chien-Cheng Kuo - chair
  • Jim-Long Her - co-chair
  • Wen-Hsien Li - co-chair
  • Jiunn-Yuan Lin - co-chair
  • Hung-Duen Yang - advisor
  • Files
  • etd-0018117-174238.pdf
  • Indicate in-campus at 1 year and off-campus access at 1 year.
    Date of Submission 2017-01-19

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