A strong ferroelectric ferromagnet created by means of spin-lattice coupling
A strong ferroelectric ferromagnet created by means of spin-lattice coupling
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DOI：
10.1038/nature09331
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发表时间：
2010-08-19
期刊：
影响因子：
64.8
通讯作者：
Schlom, Darrell G.
中科院分区：
文献类型：
--
作者：
Lee, June Hyuk;Fang, Lei;Schlom, Darrell G.
铁电铁磁体是非常罕见的，从根本上有趣的多铁性材料，可以引起新技术，其中场效应电子学的低功率和高速度与压控铁磁性的永久性和可布线性相结合（1，2）。此外，同时表现出这些现象（1-5）的少数化合物的性质与有用的铁电体或铁磁体的性质相比是微不足道的：它们的自发极化或磁化小1,000倍或更多。这同样适用于磁场或电场诱导的多铁性（6-8）。由于单相多铁性材料的弱性能，涉及应变耦合压电和磁致伸缩组件的复合材料和多层方法是目前最接近应用的方法（1，2）。然而，最近提出了一种新的铁电铁磁体的方法，通过这种方法，既不是铁电体也不是铁磁体的磁性有序绝缘体被转化为铁电铁磁体，使用单一的控制参数，应变。预计目标系统EuTiO 3在大的双向压缩应变下同时表现出强铁磁性（自发磁化，类似于每个Eu 7个波尔磁子）和强铁电性（自发极化，类似于10 μ C cm（-2））（9）。这些值比任何已知的铁电铁磁体的值高几个数量级，并且可以与仅为铁电或铁磁的最佳材料相媲美。由于缺乏合适的基底来提供所需的压缩，我们转向拉伸应变。在这里，我们表明实验和理论上的双轴张力下的多铁性状态的出现与意想不到的好处，甚至更低的应变是必需的，从而允许更厚的高品质的结晶膜。这种强铁磁铁电体的实现为这种自旋-晶格耦合机制的高温表现指明了方向（10）。我们的工作表明，单个实验参数（应变）同时控制多个序参数，并且是用于创建多铁性的成分（11）的可行替代调谐参数。
Ferroelectric ferromagnets are exceedingly rare, fundamentally interesting multiferroic materials that could give rise to new technologies in which the low power and high speed of field-effect electronics are combined with the permanence and routability of voltage-controlled ferromagnetism(1,2). Furthermore, the properties of the few compounds that simultaneously exhibit these phenomena(1-5) are insignificant in comparison with those of useful ferroelectrics or ferromagnets: their spontaneous polarizations or magnetizations are smaller by a factor of 1,000 or more. The same holds for magnetic-or electric-field-induced multiferroics(6-8). Owing to the weak properties of single-phase multiferroics, composite and multilayer approaches involving strain-coupled piezoelectric and magnetostrictive components are the closest to application today(1,2). Recently, however, a new route to ferroelectric ferromagnets was proposed(9) by which magnetically ordered insulators that are neither ferroelectric nor ferromagnetic are transformed into ferroelectric ferromagnets using a single control parameter, strain. The system targeted, EuTiO3, was predicted to exhibit strong ferromagnetism (spontaneous magnetization, similar to 7 Bohr magnetons per Eu) and strong ferroelectricity (spontaneous polarization, similar to 10 mu C cm(-2)) simultaneously under large biaxial compressive strain(9). These values are orders of magnitude higher than those of any known ferroelectric ferromagnet and rival the best materials that are solely ferroelectric or ferromagnetic. Hindered by the absence of an appropriate substrate to provide the desired compression we turned to tensile strain. Here we show both experimentally and theoretically the emergence of a multiferroic state under biaxial tension with the unexpected benefit that even lower strains are required, thereby allowing thicker high-quality crystalline films. This realization of a strong ferromagnetic ferroelectric points the way to high-temperature manifestations of this spin-lattice coupling mechanism(10). Our work demonstrates that a single experimental parameter, strain, simultaneously controls multiple order parameters and is a viable alternative tuning parameter to composition(11) for creating multiferroics.