Strain-Induced Domain Structure and Its Impact on Magnetic and Transport Properties of Gd0.6Ca0.4MnO3 Thin Films

The evolution of lattice strain on crystallographic domain structures and magnetic properties of epitaxial low-bandwidth manganite Gd0.6Ca0.4MnO3 (GCMO) films have been studied with films on different substrates: SrTiO3, (LaAlO3)0.3(Sr2AlTaO6)0.7, SrLaAlO3, and MgO. The X-ray diffraction data reveals that all of the films, except the films on MgO, are epitaxial and have an orthorhombic structure. Cross-sectional transmission electron microscopy (TEM) shows lattice mismatch-dependent microstructural defects. Large-enough tensile strain can increase oxygen vacancies concentration near the interface and can induce vacancies in the substrate. In addition, a second phase was observed in the films with tensile strain. However, compressive strain causes dislocations in the interface and a mosaic domain structure. On the other hand, the magnetic properties of the films, including saturation magnetization, coercive field, and transport property depend systematically on the substrate-induced strain. Based on these results, the choice of appropriate substrate is an important key to obtaining high-quality GCMO film, which can affect the functionality of potential device applications.

本研究针对在不同衬底上外延生长的低带宽锰氧化物Gd0.6Ca0.4MnO3（GCMO）薄膜，系统探究了晶格应变对其晶体畴结构与磁性能的演化规律，所采用的衬底包括钛酸锶SrTiO3、(LaAlO3)0.3(Sr2AlTaO6)0.7、锶镧铝氧SrLaAlO3以及氧化镁MgO。X射线衍射（X-ray diffraction）测试结果表明，除氧化镁衬底上的薄膜外，其余所有薄膜均为外延生长且具有正交晶系结构。横截面透射电子显微镜（Cross-sectional transmission electron microscopy, TEM）观测发现，存在与晶格失配相关的微观结构缺陷。足够大的拉应力应变可提升界面附近的氧空位浓度，并诱发衬底内部产生空位；此外，在受拉应变的薄膜中还观测到了第二相。与之相对，压应力应变会在界面处引发位错，并形成马赛克畴结构。另一方面，薄膜的磁性能（包括饱和磁化强度、矫顽场）与输运性能均随衬底诱导的应变呈现系统性变化。基于上述研究结果，选择合适的衬底是制备高质量GCMO薄膜的关键所在，该因素会对潜在器件应用的功能性能产生影响。