層間交換耦合(interlayer exchange coupling,IEC)的效應源自於兩個磁性層間插入一個非磁性間隔層的結構,其在自旋電子器件的研究中具有基本的物理及廣泛的實際應用。人工反鐵磁(synthetic antiferromagnetic,SAF)結構由於層間交換耦合的效應,一直被成功地運用於磁性感測器和磁性隨機存取存儲器元件中。近年來,具垂直磁異向性(perpendicular magnetic anisotropy,PMA)的多層膜被運用於低微度記憶元件時,因為其具有相當大的強磁穩定性、高信息密度優勢、開關的可靠性而備受關注。因此,具有層間交換耦合效應的人工反鐵磁結構,其應用目標便為垂直式的磁化自旋閥或磁隧道結。 然而具垂直磁異向性的人工反鐵磁結構,其結構、磁性及界面特性明顯不同於水平磁異向性。我們展開對MgO/CoFeB/Ru/CoFeB/MgO 垂直人工反鐵磁結構的綜合研究,以實驗證明層間交換耦合的行為和CoFeB厚度是非常相關的。我們也研究相關的介面效應影響,如死層厚度和CoFeB/Ru與Ru/CoFeB介面之間的差異對人工反鐵磁結構的層間交換耦合行為。這些實驗結果將提供有用的信息使得垂直磁電阻器件的設計具有更好的磁性能和熱穩定性。
We extend our previous studies of synthetic antiferromagnetic (SAF) structure MgO/CoFeB/Ru/CoFeB/MgO on the exchange coupling between ferromagnetic layers by varying the thickness of either the top CoFeB or the bottom CoFeB, respectively. The magnetization measurements of these films showed a clear variation of both remanence and saturation filed indicating the change of the exchange coupling (J) between the ferromagnetic layers. The oscillation of J as a function of CoFeB thickness is identified. We then extend the study further to a magnetic tunnel junction (MTJ) with the reference/free layer replaced by the SAFs. The magneto-resistance of the MTJ trilayer structure is measured and the reduction of the dipolar interaction will be discussed in detail.