氧化鈷在11原子鈷層/矽(111)上交換偏移相圖與鈷在銀(√3×√3)/矽(111)之磁性研究

Abstract

整個論文架構分為三大主題：即「超高真空系統之搬遷與設置」、「y ML CoO/11 ML Co/Si(111)」和「y ML Co/Ag/Si(111)- √3 × √3」之研究。「超高真空系統之搬遷與設置」包括腔體拆解、組裝與表面物理實驗室的規劃以及採取各個步驟和設計流程的原因。在反鐵磁層與鐵磁層「y ML CoO/11 ML Co/Si(111)」研究當y = 5、10、15時，其交換偏移作用是屬於哪一種類型(HE不為零或者Hc變大)，實驗的方法是採用「零場冷卻」與「場冷卻」兩種方式來對照，並期許能將實驗結果彙整成交換偏移相圖。「y ML Co/Ag/Si(111)- √3 × √3」先將Ag與Si(111)形成結構為√3 × √3的表面合金，之後再鍍上不同層數的Co膜，以磁光柯爾效應儀研究一系列磁性行為的變化。在反鐵磁層與鐵磁層系統「y ML CoO/11 ML Co/Si(111)」研究結果，在y ≤ 10時，是屬於Hc變大之交換偏移模型，其原因為低層數CoO以奈米顆粒的方式堆積，使得其磁異向性相較外加場來說是比較小，因此會讓柯爾訊號Hc增大。在y ≥ 15時，是屬於HE不為零之交換偏移模型，其原因為高層數CoO在11 ML Co/Si(111)上形成膜，使得其磁異向性相較外加場來說是比較大，因此會讓柯爾訊號HE不為零，最後，彙整交換偏移相圖，交換偏移相圖中分成三個相位，即HE不為零之交換偏移、Hc變大之交換偏移和沒發生交換偏移。「y ML Co/Ag/Si(111)- √3 × √3」研究結果，雖然在y＜4.38時沒量測到縱向柯爾訊號，然而從4.38 ≤ y≤10.21之縱向柯爾訊號做線性推斷其通過原點，表示Ag與Si(111)形成Ag/Si(111)- √3 × √3表面合金之後，能有效消除死層，阻止Co與Si(111)形成矽化物。且在4.38≦y≦10.21時，鍍於表面合金Ag/Si(111)- √3 × √3上的Co膜其易磁化軸為水平方向。在其相轉變研究方面，3.65 ML Co/ Ag/Si(111)- √3 × √3 (Ag的殘存量0.48 ML)推估其居里溫度約在275 K到300 K之間，3.51 ML Co/ Ag/Si(111)- √3 × √3系統(其中Ag的殘存量為0.53 ML)中，3.51 ML Co的厚度仍然太薄，3.51 ML Co/ Ag/Si(111)- √3 × √3的居里溫度可以推估小於150 K。In this thesis, we focus on the physical properties of CoO/Co/Si(111) and Co/Ag-Si √3 × √3/Si(111) systems. For CoO/Co/Si(111) with CoO thickness between 5 and 15 monolayers (ML), a phase diagram of the exchange bias has been established by way of comparing the results of zero-field cooling and field cooling. For CoO thinner than 10 ML, enhanced coercivity is observed because of the existence of nano-sized CoO particles at the interface. For CoO thicker than 15 ML, non-zero exchange field is observed because the magnetic anisotropy is large enough. For a Co/Ag-Si √3 × √3/Si(111) system, Co overlayer has been deposited on the top of Ag-Si √3 × √3/Si(111) surface alloy. For Co thinner than 4.38 ML, no Kerr signal isdetected in the longitudinal configuration. The easy axis of magnetization for Co/Ag-Si √3 × √3/Si(111) is in the surface plane. By extrapolating the data for Kerr signal versus the Co thickness, the zero intercept shows no magnetic dead layer. This shows that the Ag-Si √3 × √3/Si(111) surface alloy is efficient for preventing the silicide formation between the Co layer and the silicon substrate. From the cryogenic treatments of the specimens, the Curie temperature of 3.65 ML Co/Ag-Si √3 × √3/Si(111) is between 275 and 300 K. while that of 3.51 ML Co/Ag-Si √3 × √3/Si(111) is below 150 K. In addition, my designs and efforts on the movement and reestablishment of the ultrahigh vacuum system have been discussed.