Phase-driven magneto-structural properties of Co2FeAl thin films investigated by x-ray magnetic spectroscopy
| Autor: | Lin, Yen-Cheng, 林彥丞 |
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| Rok vydání: | 2015 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 104 Heusler (X2YZ) compounds are a remarkable class of materials exhibiting half-metallicity carrying highly spin-polarized electrons. Their extremely flexible electronic structure offers a versatile toolbox allowing the realization of demanded but apparently contradictory functionalities within one ternary compound. One of the most prominent applications of Heusler is the combination of magnetism and exceptional transport properties in spintronic devices, such as magnetic tunnel junction (MTJ), of which the ferromagnetic/oxide heterostructure enables a novel quantum-level transport. In this thesis the phase-driven (A2→B2) magneto-structural properties of Co2FeAl (CFA)/MgO MTJ-like structure was intensively investigated by synchrotron-based x-ray techniques. Given the advantage of x-ray’s element-specificity, we were able to fingerprint the structural and magnetic cross-reactions between Co and Fe within the complex Heusler X2YZ interpenetrating FCC structure deposited the MgO (001) substrate. From x-ray results we discovered that the two magnetic elements interacted in a competing manner via a charge transfer effect, by which Co/Fe’s spin-polarization was promoted/suppressed while the CFA underwent a A2→B2 structural transition. The charge transfer effect had raised an undesired trade-off during the Co-Fe exchange interactions despite an overall increase of the CFA’s magnetization accompanied by anisotropy modifications, because of the twice number of the X site (Co) to the Y site (Fe) in the X2YZ formula. In other words, the CFA’s magnetic ordering is unfortunately regulated by compromising the enhanced X (Co) site and the suppressed Y (Fe) site, irrespective the development of the previously known, higher spin-polarization phase of B2. We suggest an electronic tuning between the X and Y sites is critical towards the realization for this material being applicable in spintronic technology. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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