Rajapitamahuni A, Zhang L, Koten M A, Singh V R, Burton J D, Tsymbal E Y, Shield J E, Hong X
Department of Physics and Astronomy, University of Nebraska-Lincoln, Lincoln, Nebraska 68588-0299, USA.
Department of Mechanical & Materials Engineering, University of Nebraska-Lincoln, Lincoln, Nebraska 68588-0299, USA.
Phys Rev Lett. 2016 May 6;116(18):187201. doi: 10.1103/PhysRevLett.116.187201. Epub 2016 May 2.
The relatively low magnetocrystalline anisotropy (MCA) in strongly correlated manganites (La,Sr)MnO_{3} has been a major hurdle for implementing them in spintronic applications. Here we report an unusual, giant enhancement of in-plane MCA in 6 nm La_{0.67}Sr_{0.33}MnO_{3} (LSMO) films grown on (001) SrTiO_{3} substrates when the top 2 nm is patterned into periodic stripes of 100 or 200 nm width. Planar Hall effect measurements reveal an emergent uniaxial anisotropy superimposed on one of the original biaxial easy axes for unpatterned LSMO along ⟨110⟩ directions, with a 50-fold enhanced anisotropy energy density of 5.6×10^{6} erg/cm^{3} within the nanostripes, comparable to the value for cobalt. The magnitude and direction of the uniaxial anisotropy exclude shape anisotropy and the step edge effect as its origin. High resolution transmission electron microscopy studies reveal a nonequilibrium strain distribution and drastic suppression in the c-axis lattice constant within the nanostructures, which is the driving mechanism for the enhanced uniaxial MCA, as suggested by first-principles density functional calculations.
强关联锰氧化物（La，Sr）MnO₃中相对较低的磁晶各向异性（MCA）一直是将其应用于自旋电子学领域的主要障碍。在此，我们报道了一个不同寻常的现象：当在（001）SrTiO₃衬底上生长的6纳米La₀.₆₇Sr₀.₃₃MnO₃（LSMO）薄膜的顶部2纳米被图案化为宽度为100或200纳米的周期性条纹时，其面内MCA会大幅增强。平面霍尔效应测量表明，对于未图案化的LSMO，沿〈110〉方向的一个原始双轴易轴上叠加了一个新出现的单轴各向异性，在纳米条纹内各向异性能量密度增强了50倍，达到5.6×10⁶ erg/cm³，与钴的值相当。单轴各向异性的大小和方向排除了形状各向异性和台阶边缘效应作为其起源。高分辨率透射电子显微镜研究揭示了纳米结构内的非平衡应变分布以及c轴晶格常数的急剧减小，这正如第一性原理密度泛函计算所表明的，是增强单轴MCA的驱动机制。
