鐵鈀合金在石墨烯上的表面形貌與磁性

Abstract

近年來石墨烯由於其較長的自旋散射距離，成為自旋電子學中備受關注的二維材料之一，為了解決CVD製成的大範圍單層石墨烯，因電極與石墨烯間的接觸電阻，使得其傳輸自旋電子流的效果不佳，因此如何提高自旋電子注入效率成為主要研究目標。較佳的做法為使用磁性材料當作電極，磁化後並注入電流以提高自旋電子注入效率。本研究著重於了解鐵鈀合金在石墨烯上的磁性表現與表面形貌，作為往後工業應用上的基礎。本研究使用原子力顯微鏡的接觸模式，清理轉印過後石墨烯上的殘留顆粒，發現鐵鈀合金在清理過後的石墨烯上表面粗糙度僅有些微下降，而矯頑場上升約5 Oe。此外在分析不同厚度的鐵鈀合金在石墨烯上的表面形貌及磁性表現後，發現在厚度較低時鐵鈀合金的成長模式對於基板材料相當敏感，而當鐵鈀合金厚度為8 nm時表現趨於穩定。根據以上結果進一步製作元件以量測其磁阻，發現石墨烯對於鐵鈀合金的磁阻表現也有相當程度的影響，其磁阻變化率下降10倍。這些結果將有助於未來對於石墨烯和磁性材料異質結構的研究發展。Recently, graphene has been proposed for spintronic applications due to its long spin diffusion length. However, the contact resistance between single layer graphene produced via chemical vapor deposition(CVD) and electrodes leads to the poor efficiency of spin current transportation. Hence, increasing spin injection efficiency is garnered particular attention. Taking magnetized magnetic materials as electrodes then applying current through is a feasible scheme. In this study, magnetism and morphology of FePd alloy on graphene are researched to be the foundation of industry applications.In this study, atomic force microscopy(AFM) is used to clean up the residuals on transferred graphene. There are little decrease in roughness and 5 Oe increase in coercivity of FePd alloy on cleaned graphene. Furthermore, in the analysis of morphology and magnetism of different thickness FePd alloy, it is found the growth pattern of FePd alloy is sensitive to substrate and it tends to be stable while FePd alloy is 8 nm thick. Base on the above results, a magnetoresistance measurement is applied to FePd alloy on graphene. As a result, there is a 10 times decrease in magnetoresistance of it. These results are helpful for the research of graphene and magnetic materials heterostructures.