Bolstad T, Lysne E, Hallsteinsen I, Arenholz E, Österberg U L, Tybell T
Department of Electronic Systems, NTNU Norwegian University of Science and Technology, 7491 Trondheim, Norway.
J Phys Condens Matter. 2018 Jun 27;30(25):255702. doi: 10.1088/1361-648X/aac468. Epub 2018 May 14.
Using strain, i.e. subtle changes in lattice constant in a thin film induced by the underlying substrate, opens up intriguing new ways to control material properties. We present a study of the effects of strain on structural and ferromagnetic properties of (1 1 1)-oriented LaSrMnO epitaxial thin films grown on NdGaO, SrTiO, and DyScO substrates. (The subscript pc denotes the pseudo-cubic symmetry.) The results show that LaSrMnO assumes a monoclinic unit cell on NdGaO and DyScO and a rhombohedral unit cell on SrTiO. For LaSrMnO on NdGaO and DyScO a uniaxial magnetic anisotropy is found, while LaSrMnO on SrTiO is magnetically isotropic. The Néel model is used to explain the anisotropy of the thin films on NdGaO and SrTiO, however, for LaSrMnO on DyScO the effect of octahedral rotations needs to be included through the single ion model. Through examination of the Curie temperature of the strained films we suggest that (1 1 1)-strain has a different effect on the Jahn-Teller splitting of e and t electron levels than what is seen in (0 0 1)-oriented LaSrMnO thin films.
利用应变，即由底层衬底引起的薄膜晶格常数的细微变化，开辟了控制材料特性的有趣新途径。我们对在NdGaO、SrTiO和DyScO衬底上生长的（1 1 1）取向的LaSrMnO外延薄膜的应变对其结构和铁磁特性的影响进行了研究。（下标pc表示伪立方对称性。）结果表明，LaSrMnO在NdGaO和DyScO上呈现单斜晶胞，在SrTiO上呈现菱面体晶胞。对于NdGaO和DyScO上的LaSrMnO，发现其具有单轴磁各向异性，而SrTiO上的LaSrMnO是磁各向同性的。奈尔模型用于解释NdGaO和SrTiO上薄膜的各向异性，然而，对于DyScO上的LaSrMnO，需要通过单离子模型考虑八面体旋转的影响。通过检查应变薄膜的居里温度，我们认为（1 1 1）应变对e和t电子能级的 Jahn-Teller分裂的影响与（0 0 1）取向的LaSrMnO薄膜中观察到的不同。
