Ferromagnetic resonance study on the perpendicular magnetic anisotropic CoFeB synthetic ferrimagnet
| Autor: | You-Sheng Chen, 陳友生 |
|---|---|
| Rok vydání: | 2013 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 101 CoFeB alloy thin film has attracted a lots of attention because its’ unique magnetic properties. Together with high tunneling magnetoresistance ratio (TMR), perpendicular magnetic anisotropy (PMA) and low magnetic damping, CoFeB (CFB) is a good candidate to be applied in spintronic devices, such as spin-torque-transfer (STT) memory devices, STT oscillator and high sensitive magnetic sensors. However, PMA of this kind of MgO/CFB/normal-metal structure is highly dependent on synthesis process. This problem lead to two issues: First, interfacial inhomogeneity is an important factor, but common used static methods are not sensitive to magnetic inhomogeneity. This makes it hard to discuss the mechanism of anisotropy resulted from different synthesis condition. Secondly, this highly process dependency makes it hard to predict the magnetic properties of each CFB layer in synthetic ferrimagnet (SyF) structure. Up to now, most design of SyF structures is still based on the single layer characterization. In this work, ferromagnetic resonance (FMR) is utilized to study CFB thin film system dynamically to identify the accurate magnetic anisotropy, the inhomogeneity and the magnetization of each layer in SyF structures. Research steps and related results are composed as follow. First part, single layer CFB with capping and buffer Ta layers are studied, revealing that the interfacial inhomogeneity of CFB/Ta depends on the thickness of CFB. Second part is a study on MgO/CFB/Ta and Ta/CFB/MgO structures with PMA. FMR results show the difference in high order magnetic anisotropy and interface mixture between these two structures with different sequence of stacking. Third part is a study on CFB SyF without MgO. Our results show a strong influence of spacing Ta layer on both top and bottom CFB layer yielding different anisotropy and magnetization. Forth part contains results of MgO/CFB/Ta/CFB/MgO with PMA in various thickness of Ta-layer, showing an orthogonal configuration and a significant difference of magnetization between two CFB layers. Last part is the study on MgO/CFB/Ru/CFB/MgO. Comparison of Ru and Ta demonstrates a different rate of magnetization-suppression and a different degree of crystallization, which are the main reasons for different magnetic anisotropy in two CBF layers. In conclusion, our study shows the method of FMR is an effective way to identify the interfacial inhomogeneity and crystallization of CFB, influenced by the type and thickness of neighbor metal layer and the order of deposition. Furthermore, FMR detects a significant difference of magnetic anisotropy between half MgO/CFB/Ta structures and full SyF. These results could be applied for the pre-testing of magnetic multilayeres for the future design of spintronic devices. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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