Tuning the magnetic properties of LaCoO3 thin films by epitaxial strain
Tuning the magnetic properties of LaCoO3 thin films by epitaxial strain
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DOI：
10.1103/physrevb.77.014434
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发表时间：
2008-01-01
影响因子：
3.7
通讯作者：
von Loehneysen, H.
中科院分区：
文献类型：
--
作者：
Fuchs, D.;Arac, E.;von Loehneysen, H.
外延应变可以诱导LaCoO3 （LCO）薄膜的铁磁有序。在这里，我们发现LCO薄膜的磁性可以通过在不同衬底材料上的外延生长而“调谐”，即（001）取向的SrLaAlO4、LaAlO3、SrLaGaO4、（LaAlO3）（0.3）（Sr2AlTaO6）（0.7）和SrTiO3。在室温下，衬底a(s)和本体LCO a(b)之间的面内晶格参数的晶格失配范围为-1.31%至+2.63%。利用脉冲激光沉积技术在这些衬底上生长出了< 001 >取向的单相LCO薄膜。由于LCO与衬底之间的热膨胀系数存在差异，在T-s=650℃下沉积后，薄膜在冷却过程中经历了约+0.3%的额外拉伸应变，薄膜晶格参数表现出弹性行为，即随着a(s)的增加，膜内晶格参数增加。由面外应变与面内应变之比，我们得到泊松比nu近似于1/3。所有的薄膜都显示铁磁跃迁，这是由磁化测量确定的。磁化强度随着拉伸应变的增加而增加，而转变温度T-C在初始快速上升后趋于饱和，在a=3.86埃以上的T-C约为85 K。顺磁态的有效磁矩mu（eff）作为平均晶格参数< a >的函数几乎线性增加，表明高自旋态（即中自旋态或高自旋态）的填充增强。实验结果表明，随着拉伸应变的增加，八面体位旋转减小。
Ferromagnetic order can be induced in LaCoO3 (LCO) thin films by epitaxial strain. Here, we show that the magnetic properties can be "tuned" by epitaxial strain imposed on LCO thin films by the epitaxial growth on various substrate materials, i.e., (001) oriented SrLaAlO4, LaAlO3, SrLaGaO4, (LaAlO3)(0.3)(Sr2AlTaO6)(0.7), and SrTiO3. The lattice mismatch at room temperature of the in-plane lattice parameters between the substrate, a(s), and bulk LCO, a(b), ranges from -1.31% to +2.63%. Single-phase, < 001 > oriented LCO thin films were grown by pulsed laser deposition on all these substrates. Due to the difference of the thermal-expansion coefficients between LCO and the substrates, the films experience an additional tensile strain of about +0.3% during the cooling process after the deposition at T-s=650 degrees C. The film lattice parameters display an elastic behavior, i.e., an increase of the in-plane film lattice parameter with increasing a(s). From the ratio between the out-of-plane and in-plane strain, we obtain a Poisson ratio of nu approximate to 1/3. All films show a ferromagnetic transition as determined from magnetization measurements. The magnetization increases strongly with increasing tensile strain, whereas the transition temperature T-C after a rapid initial rise appears to saturate at T-C approximate to 85 K above a=3.86 angstrom. The effective magnetic moment mu(eff) in the paramagnetic state increases almost linearly as a function of the mean lattice parameter < a >, indicating an enhanced population of higher spin states, i.e., intermediate- or high-spin states. The experimental results are discussed in terms of a decrease of the octahedral-site rotation with increasing tensile strain.