在二維材料系統和層間交換耦合系統中使用渦旋光改變其磁各向異性
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2020
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本研究將拉蓋爾-高斯(Laguerre-Gaussian, LG)光束照射在磁性材料上，藉以探討帶有軌道角動量的渦旋光應用於「磁-光記憶元件」的可行性。首先，選用層間交換耦合系統的原因是因為其上下層磁性材料之磁矩，可以藉由中間過渡金屬層而互相耦合成平行、反平行或垂直而有非揮發性的記憶特性，因此有利於用來觀察記錄光對於材料的影響。另一方面，LG光束的電場、磁場與偏振光不同的是其在空間中分布不均勻的特性，在光照區域裡被預期有環形電流與衍生之局部性磁場，具有相當大的潛力能如同光的自旋角動量般，運用於光儲存元件。實驗結果顯示，渦旋光確實可以偏轉層間交換耦合系統的磁易軸，偏轉的方向也與光的軌道角動量方向有關連，本文也針對其偏轉的現象提出三種可能的機制。這項觀察亦可推廣至「鐵磁材料-二維材料異質性介面」，由於鈷和單層二硫化鉬之間因為「鈷-硫」鍵結有自旋軌道耦合，使得鈷和二硫化鉬結合時會交互耦合。其介面的強耦合也可以使用來記錄磁性的改變。經實驗發現，照射LG光束後磁各向異性也會隨之變化。間接證明了磁性材料與二維材料的結合也可以用來當作一種新的磁儲存的結構。
In this study, we introduce the Laguerre-Gaussian (LG) beam on magnetic materials to study the possibility of applying orbital angular momentum (OAM) of light to the "magneto-optical memory devices". For an interlayer exchanged coupling (IEC) system, the magnetizations of the upper and bottom magnetic materials layer coupled to each other with parallel, antiparallel, or perpendicular alignments through the intermediate transition metal layer. Because of its non-volatile memory properties, the IEC system is beneficial for observing the consequence of the twisted light illumination. On the other hand, the electric field and magnetic field of an LG beam have the helical vortex property, so we expect a ring current and induced local magnetic field appearing when the LG beam illuminates on sample's surface. The experimental results show that light with OAM can indeed deflect the magnetic easy axis of the IEC system, and the direction of the rotation is related to the sign of the topological charge. In this thesis, I propose three possible mechanisms for explaining this phenomenon. This observation can also be extended to the "ferromagnetic material-two-dimensional material heterogeneous interface". According to the previous publication, Co and MoS2 are coupled together through the "Co-S" bonding. It is found that the magnetic anisotropy will also be changed after the LG beam irradiation. This indicates the combination of magnetic materials and two-dimensional TMDCs materials has the potential to be a new type of magnetic storage material.
In this study, we introduce the Laguerre-Gaussian (LG) beam on magnetic materials to study the possibility of applying orbital angular momentum (OAM) of light to the "magneto-optical memory devices". For an interlayer exchanged coupling (IEC) system, the magnetizations of the upper and bottom magnetic materials layer coupled to each other with parallel, antiparallel, or perpendicular alignments through the intermediate transition metal layer. Because of its non-volatile memory properties, the IEC system is beneficial for observing the consequence of the twisted light illumination. On the other hand, the electric field and magnetic field of an LG beam have the helical vortex property, so we expect a ring current and induced local magnetic field appearing when the LG beam illuminates on sample's surface. The experimental results show that light with OAM can indeed deflect the magnetic easy axis of the IEC system, and the direction of the rotation is related to the sign of the topological charge. In this thesis, I propose three possible mechanisms for explaining this phenomenon. This observation can also be extended to the "ferromagnetic material-two-dimensional material heterogeneous interface". According to the previous publication, Co and MoS2 are coupled together through the "Co-S" bonding. It is found that the magnetic anisotropy will also be changed after the LG beam irradiation. This indicates the combination of magnetic materials and two-dimensional TMDCs materials has the potential to be a new type of magnetic storage material.
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Keywords
渦旋光, 磁各向異性, Twisted light, Magnetic anisotropy