(The) study of coherent optical and acoustic phonons in correlated electron materials : CMR, multiferroic = 거대자기저항효과 물질과 다강체 물질에서의 결맞음 포논에 대한 연구 CMR, multiferroic

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The pump-probe experiment on manganites, which are colossal magnetoresistance materials, $La_{1/4}Pr_{3/8}Ca_{3/8}MnO_3$ and multiferroic materials, $LuMnO_3$ and $YMnO_3$ are carried out. The hole-doped rare-earth manganite, e.g. $La_{1-x}Ca_xMnO_3$, shows colossal agnetoresistance and different temperature-dependent phases. For $0.20.5$ it shows charge-ordering phase at low temperature. If substituting Pr for La in $La_{5/8}Ca_{3/8}MnO_3$, the ferromagnetic metallic and charge-ordering phases are coexist at low temperature. For this sample, $La_{1/4}Pr_{3/8}Ca_{3/8}MnO_3$, the coherent optical and acoustic phonons are observed using femtosecond pump-probe spectroscopy. emperature dependent measurements of the time-resolved optical reflectance revealed that the energy of the photoexcited electrons dissipated during relaxation to acoustic phonons, in the high-temperature paramagnetic phase, and to optical phonons, in the low-temperature charge-ordering phase. Analysis of the temperature-dependent behavior reveals that the modal amplitudes of the coherent phonons appear strongly correlated with the charge-ordering phase. Hexagonal multiferroics, $LuMnO_3$ and $YMnO_3$, are different types of rare-earth manganites. These materials have hexagonal structure in $ab$ plane and display phase transitions: a ferroelectric phase transition at high temperature $\sim$900 K, an antiferromagnetic phase transition at 90 K ($LuMnO_3$) or 80 K ($YMnO_3$). These hexagonal rare-earth manganites show multiferroic properties, which coupled electrical(ferroelectricity) and magnetic(antiferromagnetic) properties. In the $LuMnO_3$ thecoherent optical and acoustic phonons are generated above antiferromagnetic phase transition temperature ($T_{\rmN}$), while both couldn`t generated below $T_{\rm N}$. In the $YMnO_3$, the abrupt change of coherent acoustic phonon was measured. These temperature-dependent be...
Advisors
Ahn, Jae-Wookresearcher안재욱researcher
Description
한국과학기술원 : 물리학과,
Publisher
한국과학기술원
Issue Date
2010
Identifier
455322/325007  / 020037546
Language
eng
Description

학위논문(박사) - 한국과학기술원 : 물리학과, 2010.08, [ ⅸ, 95 p. ]

Keywords

multiferroic; LPCMO; coherent phonon; pump-probe; 펌프-프로브; 자기저항효과물질; 다강체; 결맞음 포논

URI
http://hdl.handle.net/10203/47652
Link
http://library.kaist.ac.kr/search/detail/view.do?bibCtrlNo=455322&flag=dissertation
Appears in Collection
PH-Theses_Ph.D.(박사논문)
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