- 學位論文
秒級與毫秒級磁場下鐵磁薄膜的磁光克爾效應響應
The magneto-optical Kerr effect response of ferromagnetic thin films driven by fields in milliseconds and in seconds.
摘要
磁光克爾效應的量測一般是在準靜磁場條件下完成。 為了瞭解在更短時間尺度下 的磁光效應行為，我們搭建了一套可以在 2.5 ms 完成一次正負脈衝磁場來量測磁光 克爾效應的系統，以及一套傳統的磁光克爾效應量測系統。 為了增加磁光效應的訊 號，我們研究了訊號大小和檢偏器角度的關係，發現較大的檢偏器角度(以最小透光 量為零)可以得到較大的訊號。 在這篇論文中，我們著重於比較外加脈衝磁場(一次 時間為2.5 ms)以及準靜磁場(一次量測時間為90 s)所量測到的數據。 實驗樣品有兩 種，分別是長條狀的(4 nm)鎳/(15 nm)鐵/矽基板，以及(4 nm)鎳/(15 nm)鈷/矽 基板，其長寬比分別為 3、 7。 結果發現脈衝磁場所量測到的結果比準靜磁場所量 測到的矯頑力大了 3 至 5 倍，其原因乃在脈衝磁場下成核條件的不同以及域牆速度 跟不上磁場變化率所導致。 除此之外，我們也發現在鈷樣品上有明顯的磁易軸與磁 難軸，但在鐵的樣品上並無此現象。
並列摘要
Magneto-Optical Kerr Effect (MOKE) is an important technique in measuring the magnetic sample. Usually, it is performed with a quasi-static magnetic field. To study the magneto-optical effect in a shorter time scale, we have built a pulsedMOKE measurement system with a pulse duration 2.5 ms, and a conventional MOKE measurement system for comparison. In order to obtain a larger signal, we studied the analyzer angle dependence of the MOKE signal, and found that a larger signal can be obtained with a larger analyzer angle deviated from the minimum transmission angle. In this thesis, we focus on the comparison between the results of pulsed-MOKE (one loop in 2.5 ms) and conventional MOKE (one loop in 90 s). The coercivity in pulsed-MOKE results is 3 to 5 times larger than that in conventional MOKE results. This is because the nucleation condition under pulsed-field is different from that under the quasi-static field, and the domain wall motion cannot keep up with changes in the magnetic field. Besides, we also found that for cobalt sample there is apparent difference of coercivity in the hard and easy axes, but there is no such difference for iron sample.