State Key Laboratory of New Ceramics and Fine Processing, School of Materials Science and Engineering, Tsinghua University, Beijing 100084, China.
National Center for Electron Microscopy in Beijing, Key Laboratory of Advanced Materials (MOE), School of Materials Science and Engineering, Tsinghua University, Beijing 100084, China.
Sci Rep. 2017 Mar 9;7:44193. doi: 10.1038/srep44193.
Barium hexaferrite (BaM) films with in-plane c-axis orientation are promising and technically important materials for self-biased magnetic microwave devices. In this work, highly oriented BaM films with different thickness and an in-plane easy axis (c-axis) of magnetization were grown on a-plane single-crystal sapphire substrates by direct current magnetron sputtering. A procedure involving seed layers, layer-by-layer annealing was adopted to reduce the substrate-induced strains and allow for the growth of thick (~3.44 μm) films. The epitaxial growth of the BaM film on sapphire was revealed by high-resolution transmission electron microscopy with dislocations being observed at the film-substrate interface. The orientation was also verified by X-ray diffraction and more notably, polarized Raman scattering. The magnetic properties and ferromagnetic resonant frequencies were experimentally characterized by a vibrating sample magnetometry and a frequency-swept ferromagnetic resonant flip-chip technique, respectively. The micron-thick BaM films exhibited a large remanence ratio of 0.92 along in-plane easy axis and a small one of 0.09 for the in-plane hard axis loop measurement. The FMR frequency was 50.3 GHz at zero field and reached 57.9 GHz under a magnetic field of 3 kOe, indicating that the epitaxial BaM films with strong self-biased behaviors have good electromagnetic properties in millimeter-wave range.
钡铁氧体（BaM）薄膜具有面内 c 轴取向，是自偏置磁微波器件有前途和重要的技术材料。在这项工作中，通过直流磁控溅射在 a 面单晶蓝宝石衬底上生长了具有不同厚度和面内易轴（c 轴）磁化的高度取向 BaM 薄膜。采用种子层、逐层退火的方法来降低衬底诱导的应变，从而允许生长厚 (~3.44μm) 薄膜。通过高分辨率透射电子显微镜观察到薄膜-衬底界面处存在位错，揭示了 BaM 薄膜在蓝宝石上的外延生长。取向也通过 X 射线衍射得到了证实，更值得注意的是，通过偏振拉曼散射得到了证实。通过振动样品磁强计和频率扫描铁磁共振翻转芯片技术分别对磁性和铁磁共振频率进行了实验表征。微米厚的 BaM 薄膜在面内易轴方向表现出较大的剩余磁化强度比 0.92，而在面内硬轴方向的测量中则较小，为 0.09。零场下的 FMR 频率为 50.3GHz，在 3kOe 磁场下达到 57.9GHz，表明具有强自偏置行为的外延 BaM 薄膜在毫米波范围内具有良好的电磁性能。
