氧化鋅稀磁性半導體及其與氧化鎳反鐵磁之交互耦合研究

ZnO-based Diluted Magnetic Semiconductor and Exchange Bias of ZnCoO/NiO

黃鑫泓(Hsin-Hung Huang)

指導教授 ： 賴志煌

國立清華大學/工學院/材料科學工程學系/碩士(2006年)

摘要

本論文利用雙離子槍濺鍍系統，以室溫製程的優勢製備出鈷摻雜的氧化鋅稀磁性半導體薄膜，並且研究其在結構性質以及磁性質上的表現。藉由XPS以及TEM的分析方法成功地排除系統中鈷原子團的存在，並且利用SQUID的量測驗證樣品為具有室溫鐵磁性的稀磁性半導體薄膜。此外，藉由氧化鎳反鐵磁的引入，探討其與氧化鋅稀磁性半導體之間的交互耦合現象。利用場冷卻的方式，我們成功地在低溫下觀察到氧化鋅稀磁性半導體與氧化鎳反鐵磁之間的交互耦合現象，其中包括了磁滯曲線同時具有的橫向以及縱向偏移現象，且其磁滯曲線偏移的方向和樣品經過場冷卻時所施加的磁場方向有極大的關聯性。藉由場冷卻效應以及溫度效應的實驗，我們可以合理地推斷，當樣品經過場冷卻後，存在於樣品中的低溫冷凝磁矩會同時貢獻到磁滯曲線的橫向以及縱向偏移，同時樣品中也存在著一般鐵磁/反鐵磁的交換異向性貢獻，並且當樣品經過場冷卻後，此交換異向性將會使磁滯曲線產生橫向的偏移，也就是一般鐵磁/反鐵磁的交換場表現，此推測可以藉由將樣品做兩段式場冷卻的方式得到合理的驗證。

關鍵字

稀磁性半導體 ； 氧化鋅 ； 氧化鎳 ； 交互耦合

並列摘要

This work has been focused on the study of structural and magnetic properties of ZnO-based diluted magnetic semiconductor (DMS) thin films. (0002) epitaxial ZnCo0.07O films were prepared by ion beam deposition (IBD) system at room temperature. The existence of Co clusters in ZnCoO was excluded successfully by XPS and TEM analysis. Room-temperature ferromagnetism of ZnCoO was clearly observed from the results of SQUID measurements. Furthermore, with the introduction of NiO antiferromagnetic layer, we observed the hysteresis loop shifts in both horizontal and vertical directions after ZnCoO/NiO samples were field-cooled to low temperature. The directions of hysteresis loop shifts were strongly related to the cooling-field directions. Combine the experimental results of field-cooling strength effect and temperature effect, we can conclude that the hysteresis loop shifts in both horizontal and vertical directions of ZnCoO/NiO samples after the field-cooling process were induced by the so-called low temperature frozen spins in ZnCoO/NiO system. Meanwhile, from the two-step cooling process for ZnCoO/NiO samples, we can conclude that the FM/AFM exchange anisotropy in ZnCoO/NiO system was also set by the field-cooling process, which can only contribute to the hysteresis loop shift in horizontal direction.

並列關鍵字

DMS ； ZnO ； NiO ； exchange coupling

參考文獻

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