Epitaxial Growth of Co Thin Films on MgO Single-Crystal Substrates
Epitaxial Growth of Co Thin Films on MgO Single-Crystal Substrates
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DOI：
10.3379/msjmag.1006r007
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发表时间：
2010
影响因子：
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通讯作者：
Y. Nukaga;M. Ohtake;Osamu Yabuhara;F. Kirino;M. Futamoto
中科院分区：
文献类型：
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作者：
Y. Nukaga;M. Ohtake;Osamu Yabuhara;F. Kirino;M. Futamoto
采用分子束外延技术在MgO（100）、（110）和（111）晶面上制备了Co外延薄膜。研究了薄膜的生长过程、结构和磁性能。Co晶体在MgO衬底上的成核取决于衬底取向和衬底温度。在MgO（100）衬底上，当温度高于300 °C时，得到了具有hcp结构的Co（112 _ 0）外延双晶薄膜，而在100 °C时，Co外延薄膜除了hcp（112 _ 0）晶体外，还含有fcc（100）晶体。在MgO（110）衬底上生长了具有面心立方结构的Co（110）单晶薄膜。在MgO（111）衬底上外延生长了由fcc（111）和hcp（0001）晶体组成的Co薄膜。随着衬底温度的升高，hcp（0001）晶体的体积比增大，而fcc（111）晶体的体积比减小。高分辨率透射电子显微镜显示，原子级尖锐的边界之间形成的Co膜和MgO衬底，其中失配位错优先引入在膜中的界面处。这种位错的存在缓解了由薄膜和衬底之间的晶格失配引起的应变。面内磁化强度反映了hcp-Co或fcc-Co大块晶体的磁晶各向异性。
Co epitaxial thin films were prepared on MgO substrates of (100), (110), and (111) planes by molecular beam epitaxy. The growth process, the film structure, and the magnetic properties were investigated. The nucleation of Co crystal on MgO substrate varies depending on the substrate orientation and the substrate temperature. On MgO(100) substrate, Co(112 _ 0) epitaxial bi-crystalline films with hcp structure are obtained at temperatures higher than 300 °C, whereas a Co epitaxial film prepared at 100 °C includes fcc(100) crystal in addition to hcp(112 _ 0) crystal. Co(110) single-crystal films with fcc structure are formed on MgO(110) substrates. Co films consisting of fcc(111) and hcp(0001) crystals epitaxially grow on MgO(111) substrates. With increasing the substrate temperature, the volume ratio of hcp(0001) crystal increases, whereas that of fcc(111) crystal decreases. High-resolution transmission electron microscopy shows that atomically sharp boundaries are formed between the Co films and the MgO substrates, where misfit dislocations are preferentially introduced in the films at the interfaces. The presence of such dislocations relieves the strains caused by the lattice mismatches between the films and the substrates. The in-plane magnetization properties reflect the magnetocrystalline anisotropy of bulk hcp–Co or fcc–Co crystal.