Co/FePS3與Pd/Mg/[Fe/Pd]n異質結構的磁性與功能性

Abstract

在本論文中，我們首先研究鐵磁/二維反鐵磁材料(Co/FePS3)異質結構的介面磁耦合，這對於未來在自旋電子元件應用中至關重要。原子力顯微鏡揭露機械剝離法製備的FePS3薄膜表面存在約單層的缺陷。隨著Co層均勻地覆蓋於FePS3層，其表面粗糙度降至~ ±0.5 奈米。在磁特性方面，Pd/Co/FePS3異質結構表現出水平磁各向同性，並且當溫度從~85 K升高到~110-120 K時，磁矯頑力急劇降低<50%，這與FePS3的尼爾溫度相似。因此，該結果支持Co和 FePS3 薄膜之間界面磁耦合的想法。隨後，即使在高達 473 K的退火後，Co和 FePS3 薄膜之間的磁耦合仍然有效。此外，X射線磁圓二色性證實了沿平行於Co薄膜磁化的方向存在非補償Fe磁矩。淨Fe磁矩應該在調控水平異向性的Co薄膜和垂直異向性的FePS3層之間的磁耦合中發揮重要作用。 在接下來的研究中，我們探討氫氣對Mg/[Fe/Pd]x/Pd和[Fe/Pd]x/Pd多層薄膜的磁性響應。我們製備了不同Fe層厚度(0.1, 0.2, 0.4 nm)和不同週期的Fe/Pd多層薄膜，並利用磁光柯爾效應在大氣和氫氣環境下觀測樣品的磁特性。實驗結果顯示Fe/Pd多層膜在大氣和真空中表現出相同的磁特性。然而當樣品暴露於1巴的氫氣後磁矯頑力迅速下降，且在氫氣環境中保持穩定。即使樣品離開氫氣環境，此氫化效應仍可維持長達約1個小時，並且該效應對磁特性的影響是可逆的。此外，在真空和氫氣環境下皆可觀測到清晰的磁域翻轉影像，與磁滯曲線的變化相呼應。緊接著，我們使用氬氣對Mg/[Fe/Pd ]x/Pd多層膜表面轟擊，以產生微小的缺陷，使得薄膜相對於原始狀態具有更強的磁性響應。The first part of this thesis is about the study of the magnetic thin film of Co was capped over the Vander Waals two-dimensional antiferromagnetic FePS3 for the study of interfacial magnetic coupling, for the future applications in spintronic devices. The exfoliated FePS3 surface was characterized by atomic force microscopy shows deformity inside ±1 monolayer stature. The coverage of Co layer over FePS3 was evenly deposited with roughness inside approximately ±0.5 nanometer. The Pd/Co/FePS3 heterostructure displayed isotropic magnetic nature in the surface plane, Furthermore the coercivity intensely reduced through<50% while the temperature was raised from ~85 kelvin to ~110-120 kelvin, that is similar to Néel temperature TN of AFM-FePS3. That result supports the idea of interfacial magnetic coupling between Co and FePS3. Even after post annealing treatment up to 200 °C the magnetic coupling was potent among cobalt and FePS3. Moreover, x-ray magnetic circular dichroism analysis proven the existence of non-compensated Fe moment towards the in-plane order that is coordinate to the magnetization direction ofCo. The net Fe-moment is presumed to act an important part in negotiate the magnetic coupling among the in-plane ferromagnetic Co and the out of plane antiferromagnetic FePS3. The next part was about the hydrogenation effect on magnetic thin films of Mg/[Fe/Pd]x/Pd and [Fe/Pd]x/Pd multilayer structures. Different periods on Fe/Pd layers were prepared and studied, the contrasting thickness of Fe layers (0.1 nm, 0.2 nm, 0.4 nm) was deposited, and MOKE measurements were performed at ambient and hydrogen environments. The prepared multilayer films exhibit the same magnetism in the atmosphere and vacuum, but magnetic coercivity changes immediately upon exposure to 1 bar of hydrogen and the magnetic properties were stable in the hydrogen environment without any fluctuation, and magnetic coercivity was reversible once the hydrogen was pumped out (i.e., during hydrogen desorption). Clear domain image was observed in vacuum conditions and a hydrogen environment, and this was consistent with the observed magnetic hysteresis loop. Mg/[Fe/Pd]x/Pd was argon sputtered to create a tiny defect, and coercivity was increased relatively compared to the pristine thin film.