Microscopic origins for stabilizing room-temperature ferromagnetism in ultrathin manganite layers
Microscopic origins for stabilizing room-temperature ferromagnetism in ultrathin manganite layers
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DOI：
10.1073/pnas.1005693107
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发表时间：
2010-06-29
影响因子：
11.1
通讯作者：
Muller, D. A.
中科院分区：
文献类型：
--
作者：
Kourkoutis, L. Fitting;Song, J. H.;Muller, D. A.
La（0.7）Sr（0.3）MnO（3）在室温下是导电铁磁体。与薄SrTiO（3）层相结合，所得到的异质结构可以用作高自旋极化的磁性隧道结存储器。然而，当收缩到低于表观临界厚度的尺寸时，结构变得绝缘，并且铁磁有序被抑制。界面自旋和电荷调制被认为会产生界面死层，从而从根本上限制了这种材料在原子级器件中的使用。这个死层的厚度以及它是否是固有的，仍然存在争议。在这里，我们使用原子分辨电子能谱来证明La（0.7）Sr（0.3）MnO（3）/SrTiO（3）多层膜的磁性和输运性质的退化与界面处的原子混合以及La（0.7）Sr（0.3）MnO（3）层中扩展的二维阳离子缺陷的存在相关（与厚膜中的三维沉淀物相反）。当这些非本征缺陷被消除时，室温下的金属铁磁性可以稳定在超晶格中五个晶胞厚的亚锰氧化物层中，从而将任何本征死层的上限设置为每个界面两个晶胞。
La(0.7)Sr(0.3)MnO(3) is a conducting ferromagnet at room temperature. Combined with thin SrTiO(3) layers, the resulting heterostructures could be used as highly spin-polarized magnetic-tunnel-junction memories. However, when shrunk to dimensions below an apparent critical thickness, the structures become insulating and ferromagnetic ordering is suppressed. Interface spin and charge modulations are thought to create an interfacial dead layer, thus fundamentally limiting the use of this material in atomic-scale devices. The thickness of this dead layer, and whether it is intrinsic, is still controversial. Here we use atomic-resolution electron spectroscopy to demonstrate that the degradation of the magnetic and transport properties of La(0.7)Sr(0.3)MnO(3)/SrTiO(3) multilayers correlates with atomic intermixing at the interfaces, and the presence of extended two-dimensional cation defects in the La(0.7)Sr(0.3)MnO(3) layers (in contrast to three-dimensional precipitates in thick films). When these extrinsic defects are eliminated, metallic ferromagnetism at room temperature can be stabilized in five-unit-cell-thick manganite layers in superlattices, placing the upper limit for any intrinsic dead layer at two unit cells per interface.