Key Laboratory of Advanced Materials, Department of Materials Science and Engineering, Tsinghua University, Beijing 100084, People's Republic of China.
J Phys Condens Matter. 2013 Mar 13;25(10):106003. doi: 10.1088/0953-8984/25/10/106003. Epub 2013 Feb 6.
We demonstrate that the uniaxial magnetic anisotropy (UMA) of amorphous CoFeB films can be tuned by crystallinity and orbital moment ratio, combining the results of magnetization reversal and ferromagnetic resonance with high-resolution transmission electron microscopy, x-ray-absorption near-edge structure and x-ray magnetic circular dichroism. Isotropic polycrystalline buffers of tungsten (W), tantalum (Ta), and copper (Cu) between CoFeB and Si(100) substrates have direct and crucial bearing on the interfacial microstructure and orbital moment ratio. Compared with Ta and Cu buffer, CoFeB with W buffer exhibits obvious UMA and has lower crystallinity at the interface and higher orbital moment. Amorphous phase distributed homogeneously in CoFeB film grown on W buffer contributes to improve the easy-axis squareness with a sharp magnetization reversal. Our demonstrations not only realize effective tuning of UMA in amorphous CoFeB, but also provide an appealing alternative buffer (W) for CoFeB-based magnetic tunnel junctions.
我们通过磁强反转和铁磁共振的实验结果，并结合高分辨率透射电子显微镜、X 射线吸收近边结构和 X 射线磁圆二色性的测量结果，证明了非晶态 CoFeB 薄膜的单轴各向异性磁各向异性（uniaxial magnetic anisotropy，UMA）可以通过结晶度和轨道磁矩比来调控。CoFeB 与 Si(100) 衬底之间的钨（W）、钽（Ta）和铜（Cu）各向同性多晶缓冲层对界面微结构和轨道磁矩比有直接且关键的影响。与 Ta 和 Cu 缓冲层相比，具有 W 缓冲层的 CoFeB 表现出明显的 UMA，并且在界面处具有较低的结晶度和较高的轨道磁矩。在 W 缓冲层上生长的 CoFeB 薄膜中均匀分布的非晶相有助于提高易轴的方形度，从而实现更陡峭的磁强反转。我们的研究不仅实现了非晶态 CoFeB 中 UMA 的有效调控，而且为 CoFeB 基磁隧道结提供了一种有吸引力的替代缓冲层（W）。
