| Summary: | 博士 === 國立交通大學 === 電子物理系 === 91 === The half-metallic ferromagnets are expected to play a signicant role in the spin-based electronic devices by virtue of the spin-polarized characteristics of the charge carriers. In particular, among these materials, CrO2 with the highest polarization (90%~98%) is the simplest half-metallic ferromagnet, consisting of only two elements. Hole-doped LaMnO3
with the second highest polarization (85%~90%) has attracted much attention recently as a result of the colossal magnetoresistance (CMR) features. Therefore, CrO2 and hole doped LaMnO3 were regarded as the study objects in this dissertation.
Firstly, we developed a novel technique to fabricate high-quality CrO2 and La2/3Sr1/3MnO3 films on silicon substrates by means of oxidizing TiN into TiO2 as buffer layer. Simultaneously, the magnetic and transport properties of the as-grownfilms were also measured. Similarly, the half-metallicity and mechanism of the magnetoresistance were
intensively investigated.
Secondly, the role played by the oxygen ions in the hole-doped LaMnO3 is still not completely understood. We prepared La2/3Ca1/3MnO3-y films with various oxygen contents
on SrTiO3 single-crystalline substrates and measured the resistivity and magnetic properties. The influence of oxygen vacancies on the transport and magnetic phase tranisitions was investigated. Furthermore, the relationship between the insulator-metal and magnetic transitions was also studied.
Finally, x-ray near-edge structure (XANES) is one of the powerful tools to probe the electronic structure and unoccupied states of the perovskite oxides. However, the
so-called self-absorption eects will distort the
uorescence-yield XANES. We took a (110)-oriented YBa2Cu3O7-y film as an example to illustrate the correcting technique
of self-absorption eects in detail. The influence of the self-absorption effects on the fluorescence-yield XANES of CrO2 and La2/3(Sr, Ca)1/3MnO3 films was investigated. The
comparison between the spectra before and after correction was also presented.
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