Moshnyaga V, Sudheendra L, Lebedev O I, Köster S A, Gehrke K, Shapoval O, Belenchuk A, Damaschke B, van Tendeloo G, Samwer K
Erstes Physikalisches Institut, Universität Göttingen, Friedrich-Hund-Platz 1, D-37077 Göttingen, Germany.
Phys Rev Lett. 2006 Sep 8;97(10):107205. doi: 10.1103/PhysRevLett.97.107205.
Epitaxial La(3/4)Ca(1/4)MnO3/MgO(100) (LCMO) thin film shows an unusual rhombohedral (R-3c) structure with a new perovskite superstructure at room temperature due to the CE-type ordering of La and Ca with modulation vector q=1/4[011]. A-site ordered film was found to be electronically homogeneous down to the 1 nm scale as revealed by scanning tunnelling microscopy/spectroscopy. In contrast, orthorhombic and A-site disordered LCMO demonstrate a mesoscopic phase separation far below the Curie temperature (TC). Unique La/Ca ordering compensates the cation mismatch stress within one supercell, a(S) approximately 1.55 nm, and enhances the electronic homogeneity. The phase separation does not seem to be a unique mechanism for the colossal magnetoresistance (CMR) as very large CMR approximately 500% was also observed in A-site ordered films.
外延生长的La(3/4)Ca(1/4)MnO3/MgO(100)（LCMO）薄膜在室温下呈现出一种不寻常的菱面体（R-3c）结构，由于La和Ca的CE型有序排列以及调制矢量q = 1/4[011]，具有一种新的钙钛矿超结构。扫描隧道显微镜/光谱表明，A位有序薄膜在1纳米尺度以下电子性质均匀。相比之下，正交晶系且A位无序的LCMO在远低于居里温度（TC）时表现出介观相分离。独特的La/Ca有序排列补偿了一个超晶胞内的阳离子失配应力，a(S)约为1.55纳米，并增强了电子均匀性。相分离似乎不是巨磁电阻（CMR）的唯一机制，因为在A位有序薄膜中也观察到了约500%的非常大的CMR。
