Pulsed laser deposition growth of heteroepitaxial YBa2Cu3O7/La0.67Ca0.33MnO3 superlattices on NdGaO3 and Sr0.7La0.3Al0.65Ta0.35O3 substrates
Pulsed laser deposition growth of heteroepitaxial YBa2Cu3O7/La0.67Ca0.33MnO3 superlattices on NdGaO3 and Sr0.7La0.3Al0.65Ta0.35O3 substrates
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DOI：
10.1103/physrevb.85.054514
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发表时间：
2012-02-27
影响因子：
3.7
通讯作者：
Bernhard, C.
中科院分区：
文献类型：
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作者：
Malik, V. K.;Marozau, I.;Bernhard, C.
用脉冲激光沉积法在NdGaO_3(110)和Sr0.7La0.3Al0.65Ta0.35O_3(001)衬底上生长了[YBa2Cu3O7(N)/La0.67Ca0.33MnO(M)](X)(YBCO/LCMO)异质外延超晶格，其中n和m是YBCO和LCMO单层数，x是双层重复数。这些衬底与YBCO和LCMO有很好的晶格匹配，而且与常用的钛酸锶不同，它们在低温下不会产生复杂的和不受控制的应变效应。用反射高能电子衍射仪原位研究了薄膜的生长动力学，用扫描电子显微镜、X射线衍射仪和中子反射仪对薄膜的结构进行了离位研究。发现各个层在长的横向距离上是平坦和连续的，具有尖锐和连贯的界面，并且具有明确定义的各个层的厚度。唯一可见的缺陷是YBCO层中的反相界，它起源于与LCMO层交界处的钙钛矿晶胞高度台阶。我们还发现，在与LCMO界面的第一个YBCO单层具有不寻常的生长动力学，并且没有CuO链层，而随后的YBCO层具有规则的Y-123结构。因此，在LCMO/YBCO和YBCO/LCMO界面处的CuO2双层膜缺少一个相邻的CuO链层，从而缺少一半的空穴掺杂存储。然而，从n=2的超晶格的电输运测量中，我们得到了界面CuO2双层膜保持导电的证据，甚至在很低的温度下表现出超导转变的开始。最后，从直流磁化强度和中子反射率测量表明，LCMO层具有很强的铁磁性。
Heteroepitaxial superlattices of [YBa2Cu3O7(n)/La0.67Ca0.33MnO3(m)](x) (YBCO/LCMO), where n and m are the number of YBCO and LCMO monolayers and x the number of bilayer repetitions, have been grown with pulsed laser deposition on NdGaO3 (110) and Sr0.7La0.3Al0.65Ta0.35O3 (001). These substrates are well lattice matched with YBCO and LCMO and, unlike the commonly used SrTiO3, they do not give rise to complex and uncontrolled strain effects at low temperature. The growth dynamics and the structure have been studied in situ with reflection high-energy electron diffraction and ex situ with scanning transmission electron microscopy, x-ray diffraction, and neutron reflectometry. The individual layers are found to be flat and continuous over long lateral distances with sharp and coherent interfaces and with a well-defined thickness of the individual layer. The only visible defects are antiphase boundaries in the YBCO layers that originate from perovskite unit-cell height steps at the interfaces with the LCMO layers. We also find that the first YBCO monolayer at the interface with LCMO has an unusual growth dynamics and is lacking the CuO chain layer, while the subsequent YBCO layers have the regular Y-123 structure. Accordingly, the CuO2 bilayers at both the LCMO/YBCO and the YBCO/LCMO interfaces are lacking one of their neighboring CuO chain layers and, thus, half of their hole-doping reservoir. Nevertheless, from electric transport measurements on a superlattice with n = 2 we obtain evidence that the interfacial CuO2 bilayers remain conducting and even exhibit the onset of a superconducting transition at very low temperature. Finally, we show from dc magnetization and neutron reflectometry measurements that the LCMO layers are strongly ferromagnetic.