Department of Materials Science and Engineering , North Carolina State University , Raleigh , North Carolina 27695 , United States.
Materials Science Division , Army Research Office , Research Triangle Park , North Carolina 27709 , United States.
ACS Appl Mater Interfaces. 2018 Jun 20;10(24):21001-21008. doi: 10.1021/acsami.8b05929. Epub 2018 Jun 11.
The multiferroic properties of mixed valence perovskites such as lanthanum strontium manganese oxide (LaSrMnO) (LSMO) demonstrate a unique dependence on oxygen concentration, thickness, strain, and orientation. To better understand the role of each variable, a systematic study has been performed. In this study, epitaxial growth of LSMO (110) thin films with thicknesses ∼15 nm are reported on epitaxial magnesium oxide (111) buffered AlO (0001) substrates. Four LSMO films with changing oxygen concentration have been investigated. The oxygen content in the films was controlled by varying the oxygen partial pressure from 1 × 10 to 1 × 10 Torr during deposition and subsequent cooldown. X-ray diffraction established the out-of-plane and in-plane plane matching to be (111) ∥ (0001) and ⟨11̅0⟩ ∥ ⟨101̅0⟩ for the buffer layer with the substrate, and an out-of-plane lattice matching of (110) ∥ (111) for the LSMO layer. For the case of the LSMO growth on MgO, a novel growth mode has been demonstrated, showing that three in-plane matching variants are present: (i) ⟨11̅0⟩ ∥ ⟨11̅0⟩, (ii) ⟨11̅0⟩ ∥ ⟨101̅⟩, and (iii) ⟨11̅0⟩ ∥ ⟨01̅1⟩. The atomic resolution scanning transmission electron microscopy (STEM) images were taken of the interfaces that showed a thin, ∼2 monolayer intermixed phase while high-angle annular dark field (HAADF) cross-section images revealed 4/5 plane matching between the film and the buffer and similar domain sizes between different samples. Magnetic properties were measured for all films and the gradual decrease in saturation magnetization is reported with decreasing oxygen partial pressure during growth. A systematic increase in the interplanar spacing was observed by X-ray diffraction of the films with lower oxygen concentration, indicating the decrease in the lattice constant in the plane due to the point defects. Samples demonstrated an insulating behavior for samples grown under low oxygen partial pressure and semiconducting behavior for the highest oxygen partial pressures. Magnetotransport measurements showed ∼36.2% decrease in electrical resistivity with an applied magnetic field of 10 T at 50 K and ∼1.3% at room temperature for the highly oxygenated sample.
多铁性混合价钙钛矿如镧锶锰氧化物（LaSrMnO）（LSMO）的特性表现出对氧浓度、厚度、应变和取向的独特依赖性。为了更好地理解每个变量的作用，已经进行了系统的研究。在这项研究中，报告了在外延氧化镁（111）缓冲 AlO（0001）衬底上外延生长厚度约为 15nm 的 LSMO（110）薄膜。研究了具有不同氧浓度的四个 LSMO 薄膜。通过在沉积和随后的冷却过程中改变氧分压从 1×10 到 1×10 托来控制薄膜中的氧含量。X 射线衍射确定了无规层和平面匹配为（111）∥（0001）和 ⟨11̅0⟩∥ ⟨101̅0⟩对于缓冲层与衬底，以及（110）∥（111）的面外晶格匹配对于 LSMO 层。对于 LSMO 在 MgO 上的生长情况，已经证明了一种新的生长模式，表明存在三种面内匹配变体：（i） ⟨11̅0⟩∥ ⟨11̅0⟩，（ii） ⟨11̅0⟩∥ ⟨101̅⟩，和（iii） ⟨11̅0⟩∥ ⟨01̅1⟩。界面的原子分辨率扫描透射电子显微镜（STEM）图像显示出一个薄的，约 2 个单层的混合相，而高角度环形暗场（HAADF）横截面图像显示出薄膜和缓冲层之间的 4/5 平面匹配以及不同样品之间相似的畴大小。对所有薄膜进行了磁性测量，并报告了随着生长过程中氧分压的降低，饱和磁化强度逐渐减小。随着氧浓度较低的薄膜的 X 射线衍射观察到平面内的层间距的系统增加，表明由于点缺陷，平面内的晶格常数减小。在低氧分压下生长的样品表现出绝缘行为，在最高氧分压下生长的样品表现出半导体行为。磁输运测量表明，在 50K 时施加 10T 的磁场时，电阻率降低了约 36.2%，在室温下约为 1.3%，对于高度氧合的样品。
