Artificial chemical and magnetic structure at the domain walls of an epitaxial oxide
Artificial chemical and magnetic structure at the domain walls of an epitaxial oxide
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DOI：
10.1038/nature13918
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发表时间：
2014-11-20
期刊：
影响因子：
64.8
通讯作者：
Noheda, B.
中科院分区：
文献类型：
--
作者：
Farokhipoor, S.;Magen, C.;Noheda, B.
纳米技术的进步需要新的材料合成方法，从而可以将材料功能控制到最小的尺度。材料研究的一个目标是增强对铁磁体 (1)、铁电体 (2) 和超导体 (3) 等材料物理特性的控制。在这种情况下，复合氧化物和无机钙钛矿很有吸引力，因为对其原子结构的轻微调整可以产生较大的物理响应并产生多种功能(4,5)。此外，这些材料通常包含铁弹性域(6)。磁畴壁处发生的固有对称性破缺会诱发磁畴本身所不具备的特性(7)，例如磁序或铁电序和其他功能，以及它们之间的耦合。此外，大畴壁密度会产生强烈的应变梯度，这也会影响材料的性能(8,9)。在这里，我们表明，由于局部应力较大，畴壁可以促进异常相的形成。从这个意义上说，畴壁可以充当纳米级化学反应器。我们在正交钙钛矿铽锰矿（TbMnO3）的磁畴壁合成了二维铁磁相，该相是在钛酸锶（SrTiO3）基板上外延应变下以薄层生长的。该相尚未通过标准化学路线产生。二维片材的密度可以通过改变薄膜厚度或基底晶格参数（即外延应变）来调节，并且在超薄膜中片材之间的距离可以小至5纳米（10），这样磁畴壁处的新相最多可占薄膜体积的25%。使用外延氧化物畴壁促进异常相形成的一般概念可能适用于其他材料系统，从而为纳米电子学和自旋电子学应用提供新型纳米级材料。
Progress in nanotechnology requires new approaches to materials synthesis that make it possible to control material functionality down to the smallest scales. An objective of materials research is to achieve enhanced control over the physical properties of materials such as ferromagnets(1), ferroelectrics(2) and superconductors(3). In this context, complex oxides and inorganic perovskites are attractive because slight adjustments of their atomic structures can produce large physical responses and result in multiple functionalities(4,5). In addition, these materials often contain ferroelastic domains(6). The intrinsic symmetry breaking that takes place at the domain walls can induce properties absent from the domains themselves(7), such as magnetic or ferroelectric order and other functionalities, as well as coupling between them. Moreover, large domain wall densities create intense strain gradients, which can also affect the material's properties(8,9). Here we show that, owing to large local stresses, domain walls can promote the formation of unusual phases. In this sense, the domain walls can function as nanoscale chemical reactors. We synthesize a two-dimensional ferromagnetic phase at the domain walls of the orthorhombic perovskite terbium manganite (TbMnO3), which was grown in thin layer sunder epitaxial strain on strontium titanate (SrTiO3) substrates. This phase is yet to be created by standard chemical routes. The density of the two-dimensional sheets can be tuned by changing the film thickness or the substrate lattice parameter (that is, the epitaxial strain), and the distance between sheets can be made as small as 5 nanometres in ultrathin films(10,) such that the new phase at domain walls represents up to 25 per cent of the film volume. The general concept of using domain walls of epitaxial oxides to promote the formation of unusual phases may be applicable to other materials systems, thus giving access to new classes of nanoscale materials for applications in nanoelectronics and spintronics.