利用鐵磁共振來研究直流濺鍍NiFe/Cu/NiFe三層膜之磁特性

Abstract

三層膜(鐵磁/非鐵磁/鐵磁)與多層膜的巨磁阻效應(GMR)主要來自於磁層之間的RKKY 偶合現象。本實驗先假設NiFe/Cu/NiFe 三層膜的自由能項，其中自由能包含︰晶格場、磁異向性能、交互作用能及靜磁能。利用角度鐵磁共振量測FMR 的角度變化關係、磁振儀(VSM) 量測樣品飽和磁化及四點探針量測磁電阻，最後擬合出NiFe/Cu/NiFe 中自由能的磁異向性係數、耦合係數和阻尼係數。 為達成研究目標，我們先建造VNA-角度鐵磁共振儀、一臺具有四支磁控濺鍍槍的超高真空濺鍍系統和加強一臺振動樣品磁力計(VSM)。VNA-角度鐵磁共振儀方面，我們使用向量網路分析儀(VNA)、高Q 值的共振腔來改進傳統鐵磁共振儀單一波段微波與低靈敏度鐵磁共振吸收的缺點。振動樣品磁力計方面，重新製作了VSM 的感應線圈(pick-up coil)，新感應線圈增加了1.5 倍的靈敏度，使VSM 能量測到更小更精準的磁化量，並且另外製作新的感應線圈座和加裝了Y 方向的感應線圈，使VSM 能同時量測樣品X 軸方向與Y 軸方向的磁化量。 我們製備了兩系列的樣品，分別為Py10nm /Cut /Py15nm /Si (t 為0.4nm~2nm)、Py10nm /Cut /Py10nm /Si (t 為0.4nm~2nm)。從角度鐵磁共振資料中的兩個吸收峰顯示了三層膜的RKKY 磁層耦合現象，MR 量測到的磁電阻變化率(%)隨著膜厚變化在0.02~0.17(%)之間振盪，VSM 量測到的矯頑場也在3 Oe~10 Oe 間振盪，擬合出的耦合係數也隨著膜厚變化在0.2~0.7 之間呈現振盪。

Giant magnetoresistance (GMR) effect of trilayer (FM/NM/FM) and multilayers are mainly result of RKKY coupling phenomenon. In the thesis, we assume a free energy model of NiFe/Cu/NiFe trilayer. The free energy is consist of following terms: crystal field, anisotropy energy, exchange energy and magneto static energy. A angular resolved ferromagnetic resonance, magneto-resistance and vibrating sample magnetometer measurement were performed. Through fitting of FMR data, we obtained uniaxial anisotropy constant, coupling energy and damping constant. For the research, we constructed a vector-network analyzer based FMR, a UHV magnetron sputtering system, and upgrade a vector VSM. Using VNA-network analyzer and resonance cavity with high Q-value, the improvement from traditional FMR and microstrip FMR are wider microwave range and high sensitivity. We also design and implement a new pick-up coil for vector VSM. The new coil result in 1.5 times of sensitivity and measurement of magnetization component both perpendicular to field and parallel to field. Two series of trilayer were fabricated which are Py10nm /Cut /Py15nm /Si (t from 0.4nm to 2nm) and Py10nm /Cut /Py10nm /Si (t from 0.4nm to 2nm). Two absorption peak of FMR data shows RKKY coupling effect, which also can observe in MR ratio versus Cu thickness. The oscillation between 0.02~0.17(%) were measured. Hc data from VSM also oscillate in range of 3 Oe ~ 10 Oe. Exchange stiffness obtained from fitting of angular FMR data oscillate either.