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X-ray Magnetic Circular Dichroism Study of Perovskite-type Manganese Oxide Thin Films
| Content Provider | Semantic Scholar |
|---|---|
| Author | Harano, Takayuki |
| Copyright Year | 2013 |
| Abstract | Transition-metal oxides (TMOs) with the perovskite-type structure have been investigated intensively over decades due to the diversity of their physical properties. Recently, one can fabricate high-quality TMO ultra-thin films by epitaxial growth methods. In such films, dramatical changes of their physical properties, such as electronic and magnetic phase transitions, are widely observed as functions of composition and lattice strain of thin films . In this thesis, I have studied coercivity enhancement by impurity doping and electronic phase transitions due to epitaxial strain in manganese-oxide thin films with the perovskite-type structure. The former topic is coercivity enhancement by Ru doping in La1−xSrxMnO3 (LSMO). LSMO has attracted attention for possible applications to magnetic tunnel junctions, but there is a serious problem that the coercivity (HC) is too small. One can enhance the coercivity by substituting Ru for Mn. In order to obtain information about electric and magnetic states of each element and to elucidate the mechanism of the coersivity enhancement, I performed xray absorption spectroscopy (XAS) and x-ray magnetic circular dichroism (XMCD) measurements. I found that the spin direction of Ru is opposite to that of Mn. Ru in LSMO was found to have a finite orbital magnetic moment unlike a nearly quenched orbital magnetic moment of Ru in SrRuO 3. The finite orbital magnetic moment of Ru will lead to a magnetic anisotropy and may be the origin of the enhancement of coercivity in the Ru-doped LSMO. Cluster-model analysis of Ru XAS and XMCD spectra indicated that the small spin magnetic moment of Ru can be explained, if a lattice distortion of theD4h symmetry under epitaxial strain is assumed in the presence of the finite spin-orbit coupling. The latter topic is spin and electronic phase transitions due to substrate epitaxial strain in Ca1−xCexMnO3 (CCMO). In CCMO, one can control the resistivity and the spin structures through substitution of Ce for Ca. One have reported that the resistivity and the spin structures of CCMO can be controlled by changing the substrates such as (001)-oriented YAlO 3 (YAO), NdAlO3 (NAO), and LaSrAlO4 (LSAO). However, Their magnetic properties have not been investigated sufficiently yet. Especially, one cannot measure magnetization of CCMO thin films on NAO substrates using a SQUID because of strong paramagnetic signals from concentrated Nd ions in the substrate. In order to identify different phases of CCMO thin films, I have studied magnetic anisotropy of Mn in CCMO thin films grown on NAO substrates. As the results, I obtained the magnetism of CCMO thin films grown on NAO substrates for the first time and I concluded the magnetic anisotropies of each thin films. They should be reflect their spin structures. |
| File Format | PDF HTM / HTML |
| Alternate Webpage(s) | http://wyvern.phys.s.u-tokyo.ac.jp/f/Research/arch/MasterThesis_Harano.pdf |
| Language | English |
| Access Restriction | Open |
| Content Type | Text |
| Resource Type | Article |
