摘要
自从高温超导铜氧化物和庞磁电阻锰氧化物被发现以来,人们对多种过渡金属氧化物块材的性质已经有了比较深入的了解,尽管很多现象背后的物理基础仍然存在激烈的争议。随着材料制备技术的突飞猛进,人们开始利用过渡金属氧化物丰富的物性去设计新的氧化物器件。氧化物界面比半导体界面的物理更丰富,晶格、电荷、自旋和(或)轨道的重构可能会导致体材料中所不存在的性质。最近,人们对LaAlO3/SrTiO3界面进行了深入研究,发现了由于电荷转移而造成的二维电子气,甚至超导电性等性质。与钛基异质结相比,锰基异质结由于引入了磁性,其物理现象应该更加丰富,可以期待电荷转移所带来的自旋极化二维电子气。本论文基于第一性原理计算,系统研究了SrMnO3(001)和(111)表面上的磁性重构,以及基于SrMnO3的相关界面上所获得的高自旋极化的二维电子气。下面我们分四部分详细归纳所得主要结果:
1.在SrMnO3本征的(001) MnO2表面,由于平移周期性破缺,表面和次表面上的Mn离子都出现d z2轨道占据,进而造成表面上的自旋反转,即表面内Mn离子反铁磁耦合,而表面与次表面间铁磁耦合。当表面氧空位浓度为25%时,表面和次表面上的Mn1离子都只有t2g轨道被占据,所以该位置层间仍是反铁磁耦合。而表面和次表面上的Mn2离子出现d z2轨道占据,该位置层间为铁磁耦合。这就造成25%表面氧空位浓度下特有的铁磁绝缘表面。当表面氧空位浓度增加到50%和75%时,表面上Mn离子的dx2y2轨道开始被占据,次表面仍是t2g和d z2轨道被占据。此时,表面也是自旋反转的。当表面氧空位浓度达到100%时,表面上Mn离子的五个3d轨道都被占据,而次表面上Mn离子,除了t2g和d z2轨道被占据外,dx2y2也开始被占据。此时, Mn离子之间超交换耦合机制起作用,由此得到G类反铁磁基态。外延应力对上述各种情况下的轨道占据和表面磁重构都没有影响。
2.在nn型LaAlO3/SrMnO3超晶格中,LaAlO3中的极化电场驱动电子从(LaO)+层转移到SrMnO3中,并占据Mn的eg轨道,符合双交换耦合机制,从而造成nn型超晶格中的半金属铁磁性。在pp型超晶格中,LaAlO3中的极化电场使空穴从LaAlO3侧转移到SrMnO3侧,并基本平均分布在氧离子上。此时,Mn离子由于没有eg轨道占据而产生类似于体材料的G类反铁磁序。不过由于空穴的掺入,此类超晶格是金属性的。当通过外加磁场使体系变为铁磁态后,体系同时表现出电荷掺杂和空穴掺杂的特征,这表明该界面上出现了异常的磁输运性质。在np型超晶格中,随着MnO2层和LaAlO3厚度的变化,出现了复杂的磁有序。且随着LaAlO3厚度的增加,体系反铁磁基态和铁磁态之间的能量差逐渐减小,所以我们预测,在np型超晶格中,增加LaAlO3厚度,就有可能使体系的基态从反铁磁变为铁磁。同时,这些结果也表明,如果我们在np型超晶格中施加外磁场,就有可能实现庞磁电阻效应。进一步计算结果表明,对nn型超晶格界面来说,氧八面体畸变并不会改变其半金属电子态,而应力则因为会改变eg轨道的占据,从而影响基态磁结构。而对pp型和np型超晶格来说,应力会增强或减弱极化电场,从而影响到电荷转移,进而影响到基态磁构型。不过,氧八面体畸变不影响pp型超晶格的基态磁结构。而在np型超晶格中,引入氧八面体畸变后有助于增强Mn离子之间的铁磁耦合。
3、在本征的以Mn为终端面的SrMnO3极性(111)表面上,由于极性灾难,表面上的Mn离子应该变为Mn2+,因此导致了(111)表面上不同的电子相。进一步研究发现,在n型LaAlO3/SrMnO3(111)超晶格中,由于SrMnO3和LaAlO3中同时存在强度不同的极化电场,导致Mn离子上不均匀分布的电子,占据eg轨道。进一步分析表明,这些电子来自于LaAlO3侧。与该体系的n型(001)超晶格类似,Mn离子之间通过双交换耦合,形成半金属铁磁性。增加SrMnO3层数,每个Mn离子的磁矩之和基本保持不变,说明转移过来的电子数是固定的常数。由于Mn的eg轨道被占据,该系统中的MnO6八面体出现旋转和倾斜。而对p型超晶格而言,SrMnO3和LaAlO3中同时存在的强度不同的极化电场使得空穴基本上是均匀分布于SrO3面和LaO3面的氧离子上,于是像体材料中那样产生G类反铁磁序,同时氧八面体基本上没有畸变。不过由于空穴的掺入,此类超晶格是金属性的。
上述结果是基于SrMnO3展开的表面与界面的相关工作,这些异常的磁性质和电性质表明在锰氧化物表面和界面上出现了新颖特性,从而预示着这些体系在自旋电子学方面将有重要应用。
Ever since the discovery of high temperature cuprates and colossal magnetoresistivemanganites, extensive investigations have been made on the transition metal oxides. Withthe growing growth of technique for material preparation, people are quite eager to designnew oxide devices by combining various transition metal oxides. Oxide interfaces havericher physics than semiconductor interfaces because of possible lattice reconstruction,charge reconstruction, spin reconstruction as well as orbital reconstruction. In many cases,the properties of these interfaces turn out to be much richer than those of their bulkconstituents. Recently, LaAlO3/SrTiO3interfaces have been studied extensively andhigh-mobility quasi two-dimensional electron gas or even superconductivity emerged dueto charge transfer. Comparing with Ti-based oxide interfaces, Mn-based oxide interfaces,which is the focus in our studies, may have richer physical phenomena due to spin degreeof freedom of Mn cation and therefore spin-polarized two dimensional electron gas can beexpected. In this thesis, based on extensive first-principle calculations, the magneticreconstructions of the SrMnO3(001) and (111) surface and heterointerface were studiedsystematically. Highly spin-polarized two dimensional electron gas was realized atSrMnO3-based heterointerfaces. The main results are summarized as follows in detail.
1. For the pristine Mn-terminated SrMnO3(001) surface, due to the symmetry broken atthe surface, surface Mn and subsurface Mn ions show the occupancy ofd z2orbital, and asa result, spin-flip AFM, FM along the c axis and AFM in the ab plane, is energeticallyfavorable. When oxygen vacancies (OVs) concentration is25%, electrons start to occupy surface andd z2orbital of subsurface Mn2, while keep the surface and egorbital ofsubsurface Mn1still empty, leading to a ferromagnetic surface. With the increasing OVs(50%and75%),dx2y2orbital of surface Mn start to be occupied, while keeping t2ganddx2y2orbital occupation of subsurface Mn. Therefore, spin-flip AFM surface is obtained.In100%case, five3d orbitals of surface Mn are completely filled, anddx2y2orbital ofsubsurface Mn also start to be occupied, so AFM superexchange dominates. As a result,bulk like G-type AFM ground state is obtained. The epitaxial strain does not change orbitaloccupancy and spin-flip process at any OV case.
2. In the nn-type LaAlO3/SrMnO3supperlattices, electrons transfer from (LaO)+layer intoSrMnO3component induced by polar electric field in LaAlO3. These transferred electronsdistribute uniformly in SrMnO3component and occupy Mn’s egorbital, inducinghalf-metallic ferromagnetism in the framework of Zener double exchange. In the pp-typeLaAlO3/SrMnO3supperlattices, the polar electric field in the LaAlO3drives holes out ofthe LaAlO3component and into SrMnO3component, which reside almost uniformly at theoxygen atoms in the superlattices. With absence of the egstates at the Mn sites, bulk-likeG-type AFM ordering were obvious. But pp-type superlattices are metallic because of holetransfer. When a magnetic field is applied to induce FM ordering, the pp-type superlatticesshow the characteristics of coexistence of electron-doping and hole-doping, suggestingunusual magnetotransport properties therein. In the np-type LaAlO3/SrMnO3supperlattices,complex magnetic orderings emerge by changing the number of MnO2layer and thicknessof LaAlO3component. With increasing LaAlO3layers, the energy difference betweenground state and FM state gets smaller and smaller, so a tendency of transition from acomplex AFM state to FM state can be expected. These results suggest that possiblecolossal magnetoresistive effects can be observed when an external magnetic field isapplied in these np-type LaAlO3/SrMnO3superlattices. Further calculations demonstrate that oxygen octahedral rotation and tilting don’t change the robust half-metallic electronicstate in nn-type LaAlO3/SrMnO3superlattices. But epitaxial strain will change the egorbital occupation, consequently, and influence ground state magnetic ordering of this kindof superlattices. For pp-type and np-type superlattices, charge transfer changessignificantly with strain due to increase (decrease) of polar field in the tensile (compressive)condition. On the other hand, oxygen octahedra rotation and tilting does not change theground-state magnetic ordering in pp-type superlattices. But oxygen rotation and tiltingstrengthen FM coupling between neighboring Mn ions in np-type superlattices.
3. For the pristine Mn-terminated SrMnO3(111) surface, due to the polarcatrosphy, Mncation at surface should be Mn2+, therefore leading to different electronic phase at the(111) surfaces. Furthermore, in the n-type LaAlO3/SrMnO3(111) supperlattices,electrons transferred from LaAlO3component distribute unevenly in SrMnO3componentand occupy Mn’s egorbital, inducing half-metallic ferromagnetism in the framework ofZener double exchange. With increasing SrMnO3layers, the sum of every Mn magmonkeep a constant suggesting a fixed number of charge transferred from LaAlO3component.With egorbital occupancy, the systems show obvious MnO6octahedron rotation andtilting. For p-type superlattices, holes reside almost uniformly at the SrO3and LaO3planedrived by the polar electric field in the LaAlO3and SrMnO3component. With absence ofthe egstates at the Mn sites, bulk-like G-type AFM ordering were obvious with almostimperceptible octahedron rotation and tilting. But p-type superlattices are metallicbecause of hole transfer.
With the above first-principle calculations and analysis, we have provided acomprehensive picture of electronic and magnetic reconstructions at the surface andinterface of SrMnO3-based heterostructures. These novel magnetic and electric propertiesdemonstrate their potential application in spintronic devices.
引文
[1] Jonker G. H., van Santen J. H., Physica,16,337(1950).
[2] Zener C., Phys. Rev.2,403(1951).
[3] Goodenough J. B., Phys. Rev.,100,564(1955).
[4] Wollan E. O., Koehler W. C., Phys. Rev.,100,545(1955).
[5] von Helmolt R., Wecker J., Holzapfel B., et al. Phys. Rev. Lett.,71,2331(1993).
[6] Jin S., Tiefel T. H., McCormack M., et al. Science,264,423(1994).
[7] Dagotto E., Hotta T. and Moreo A., Phys. Rep.344,1(2002).
[8] Tokura Y., Colossal Magnetoresistive Oxides, London, Gordon and Breach SciencePublishers,2000.
[9] Tobe K., Kimura T., Tokura Y., Phys. Rev. B.,69,014407(2004).
[10] Tokura Y., Tomioka Y., J. Magn. Magn. Mater.200,1(1999).
[11] Snyder G. J., Ron H., Phys. Rev. B.,53,14434(1996).
[12] Hwang H. Y.,Cheong S. W.,et al., Phys. Rev. Lett.,75,914(1995).
[13] Tokunaga M., Miura N., Tomioka Y., et al, Phys. Rev. B,575259(1998).
[14] Moussa F., Hennion M., et al, Phys. Rev. B,67,214430(2003).
[15] Yamada Y., Hino O., Nohdo S., Kanao R., et al, Phys.Rev. Lett.,77904(1996).
[16] Endoh Y., et al, Phys. Rev. Lett.,82,4328(1999).
[17] Radaelli P. G., Ibberson R. M., et al, Phys. Rev. B,63,172419(2001).
[18] Kpausta C., Riedi R. C., Sikora M.,et al, Phys. Rev. Lett.,84,4216(2000).
[19] Uehara M., Mori S., Chen C. H., Cheong S. W.,Nature,399,560(1999).
[20] Booth C. H., Bridges F., Kwei G. H., et al, Phys. Rev. Lett.,80,853(1998).
[21] Kajimoto K., Yoshizawa H., Shintani H., et al, Phys. Rev. B,70,012401(2004).
[22] Arima T., Tokunaga A., Goto T., et al, Phys. Rev. Lett.,96,097202(2006).
[23] Miyano K., Tanaka T., Tomioka Y., et al, Phys. Rev. Lett.,78,4257(1997).
[24] Kiryukhin V., Casa D., Hill J. P., Keimer B., et al, Nature,386,813(1997).
[25] Raveau B., Maignan A. and Martin C., J. Solid, State Chem.,130,162(1997).
[26] Asamitsu A., Tomioka Y., Kuwahara H. and Tokura Y., Nature,388,50(1997).
[27] Millis A. J., Nature (London),392,147(1998).
[28] Yunoki S., Hu J., Malvezzi A. L., et al, Phys.Rev. Lett.,80,845(1998).
[29] Moreo A., Yunoki S., Dagotto E., Science,283,2034(1999).
[30] Satadeep B., Eric B., Philippe G., Phys. Rev. Lett.,102,117602(2009).
[31] James M. R., Aaron S. E., Nicola A. S., Phys. Rev. B,79,205119(2009).
[32] Jun H. L., Karin M. R., Phys. Rev. Lett.,104,207204(2010).
[31] James M. R., Aaron S. E., Nicola A. S., Phys. Rev. B,79,205119(2009).
[33] Jahn H. A., Teller E., Proc. Roy. Soc. A,161,220(1937).
[34] Imada M., Fujimori A., et al., Rev. Mod. Phys.,70,1039(1998).
[35] Goodenough J. B., Kafalas J. A., Longo J. M., In Preparative Methods in Solid StateChemistry, Hagenmuller, p. Ed., Academic New York,1972, Chapter1.
[36] Kanamori J., J. Appl. Phys.31,14(1960).
[37] Rao C. N. R., Anthony A., et al., J. Phys.: Condens. Matter.,12, R83(2000).
[38] Valenzuela R.,1994, Magnetic Ceramics (Cambridge: Cambridge University Press).
[39] Leonov I., Yaresko A. N., et al., Phys. Rev. Lett.,93,146404(2004).
[40] Rao C. N. R., Arulraj A., Santosh P. N., et al., Chem. Mater.,10,2714(1998).
[41] Jirak Z., Krupicka S., Sinsa Z., et al., J. Magn. Magn. Mater.,53,153(1985).
[42] Chen C. H., Cox D. E., Cheong S. W., Phys. Rev. Lett.,76,4042(1996).
[43] Mori S., Chen C. H., Cheong S. W., Nature,392,473(1998).
[44] Li X. G., Zheng R. K., Li G., et al., Europhys. Lett.,60,670(2002).
[45] Sundaresan A., Paulose P. L., et al., Phys. Rev. B,57,2690(1998).
[46] Takeuchi J., Hirahara S., Dhakal T. P., et al., Physica B,754,312(2002).
[47] Babushkina N. A., Belova L. M., et al., Nature,391,159(1998).
[48] Kiryukhin V., Casa D., Hill J. P., et al., Nature,386,813(1997).
[49] Kuwahara H., Tomioka Y., et al., Science,270,961(1995).
[50] Tomioka Y., Asamitsu A., Moritomo Y., et al., Phys. Rev. Lett.,74,5108(1995).
[51] Woodward P. M., Cox D. E., et al., Chem, Mater.,11,3528(2001).
[52] Tokura Y.,Rep. Prog. Phys.,69,797(2006).
[53] Murakami Y., et al., Phys. Rev. Lett.81,582(1998).
[54] Urushibara A., Moritomo Y., et al, Phys. Rev. B.51,14103(1995).
[55] Okuda T., Asamitsu A., et al, Phys. Rev. Lett.53, R4109(1996).
[56] Tokura Y., Tomioka Y., J. Magn. Magn. Mater.200,1(1999).
[57] Moritomo Y., Akimoto T., et al, Phys. Rev. B.58,5544(1998).
[58] Jirak Z., Krupicka S., et al, J. Magn. Magn. Mater.53,153(1985).
[59] Yoshizawa H., Kawano H., et al, Phys. Rev. B.52, R13145(1995).
[60] Kawano H., Kajimoto R., Yoshizawa H., et al, Phys. Rev. Lett.78,4253(1997).
[61] Kuwahara H., Okuda T., Tomioka Y., et al, Phys. Rev. Lett.82,4316(1999).
[62] Kajimoto R., Yoshizawa H., Kawano H., et al, Phys. Rev. B.60,9506(1999).
[63] Dagotto E., Hotta T., Moreo A., Phys. Rep.344,1(2001).
[64] Burgy J., et al., Phys. Rev. Lett.,87,277202(2001).
[65] Burgy J., Moreo A., Dagotto E., Phys. Rev. Lett.,92,097202(2004).
[66] Dagotto E., Nanoscale Phase Separation and Colossal Magnetoresistance(Springer-Verlag, Berlin,2002).
[67] Louca D., Egami T., Brosha E. L., Roder H., et al., Phys. Rev. B,56, R8475(1997).
[68] De Teresa J. M., Ibarra M. R., et al., Nature (London),386,256(1997).
[69] Hennion M., Moussa F., Biotteau G., et al., Phys. Rev. Lett.,81,1957(1998).
[70] Allodi G., De Renzi R., Guidi G., Phys. Rev. B,57,1024(1998).
[71] Mori S., Chen C. H., Cheong S. W., Phys. Rev. Lett.,81,3972(1998).
[72] Yunoki S., Hu J., Malvezzi A. L., et al., Phys. Rev. B,80,845(1998).
[73] Kiryukhin V., Kim B. G., Podzorov V., et al., Phys. Rev. B,63,024420(2000).
[74] F th M., Freisem S., Menovsky A. A., et al., Science,285,1540(1999).
[75] Dagotto E., Hotta T., Moreo A., Phys. Rep.,344,1(2001).
[76] Kramers H. A., Physica,1,182(1934).
[77] Anderson, Phys. Rev.79,350(1950).
[78] Goodenough J. B., Phys. Rev.100,564(1955).
[79] Goodenough J. B., J. Phys. Chem. Solids,6,287(1958).
[80] Kanamori J., J. Phys. Chem. Solids,10,87(1959).
[81] Millise A. J., Littlewood P. B., Shraiman B. I., Phys. Rev. Lett.,74,5144(1995).
[82] Millise A. J., Shraiman B. I., Mueller R., Phys. Rev. Lett.,77,175(1996).
[83] Huang Q., Santoro A., Lynn J. W., et al., Phys. Rev. B,55,14987(1997).
[84] Ravindran P., Kjekshus A., Fjellvag H., et al., Phys. Rev. B,65,064445(2002).
[85] Hu W. Y., Qian M. C., Zheng Q. Q., et al., Phys. Rev. B,61,1223(2000).
[86] Evarestov R. A., Kotomin E. A., et al., Phys. Rev. B,72,214411(2005).
[87] Sergei P., Eckhard S., Timo J., et al., Phys. Rev. B,76,012410(2007).
[88] Sawada H., Morikawa Y., Terakura K., et al., Phys. Rev. B,56,12154(1997).
[89] Murakami Y., Hill J. P., Gibbs D., et al., Phys. Rev. Lett.,81,582(1998).
[90] Igor S., Noriaki H., Kiyoyuki T., et al., Phys. Rev. Lett.,76,4825(1996).
[91] Rodriguez-Carvajal J., Hennion M., et al., Phys. Rev. B,57, R3189(1998).
[92] Hashimoto T., Ishibashi S., Terakura K., et al., Phys. Rev. B,82,045124(2010).
[93] Andersn P. W., Science,177,393(1972).
[94] Hwang H. Y., Iwasa Y., Kawasaki M., et al., Nature Materials,11,103(2012).
[95] Takahashi K. S., Kawasaki M., Tokura Y., Appl. Phys. Lett.79,1324(2001).
[96] Ohtomo A., Muller D. A., Grazul J. L., Hwang H. Y., Nature,419,378(2002).
[97] Tokura Y., et al., Phys. Rev. Lett.,72,2126(1993).
[98] Salvador P. A., Haghiri-Gosnet A-M, et al., Appl. Phys. Lett.75,2638(1999).
[99] Yamada H., Kawasaki M., Lottermoser T., et al., Appl. Phys. Lett.80,52506(2006).
[100] Bhattacharya A., et al., Phys. Rev. Lett.,100,257203(2008).
[101] Freeland J. W., et al., Phys. Rev. B.,72,094414(2010).
[102] Pauli S. A., et al., Phys. Rev. Lett.,106,036101(2011).
[103] Salluzzo M., et al., Phys. Rev. Lett.,102,166804(2009).
[104] Pinta C., et al., Phys. Rev. B,78,174402(2008).
[105] Aruta C., et al., Phys. Rev. B,80,014431(2009).
[106] Okamoto S., Millis A. J., Nature,428,630(2004).
[107] Pentcheva R., Pickett W. E., Phys. Rev. Lett.,99,016802(2007).
[108] Chaloupka J., Khaliullin G., Phys. Rev. Lett.,100,016404(2008).
[109] Hansmann P., et al., Phys. Rev. Lett.,100,016404(2008).
[110] Seo S. S. A., et al., Phys. Rev. Lett.,104,036401(2010).
[111] Benckiser, et al., Nature Mater.,10,189(2011).
[112] Chakhalian J., et al., Nature Phys.,2,244(2006).
[113] Chakhalian J., et al., Science,318,1114(2007).
[114] Yu P., et al., Phys. Rev. Lett.,105,027201(2010).
[115] Hang H. Y., Iwasa Y., Kawasaki M., et al., Nature Mater.,11,103(2012).
[116] Tsymbal E., Dagotto E., Eom C. Ramesh R, Multifunctional OxideHererostructures (Oxford University Press, Oxford,2012).
[117] Ohtomo A., Hwang H. Y., Nature,427,423(2004).
[118] Nakagawa N., Hwang H. Y., Muller D. A., Nature Mater.,5,204(2006).
[119] Sing M., Bemer G., et al., Phys. Rev. Lett.,102,176805(2009).
[120] Bell C., Harashima S., Hikita Y., et al., Appl. Phys. Lett.,94,222111(2009).
[121] Thiel S., Hammerl G., Schmehl A., et al., Science,313,1942(2006).
[122] Bhattacharya A., May S. J., et al., Phys. Rev. Lett.,100,257203(2009).
[1] Evarestov R. A., Kotomin E. A., et al., Phys. Rev. B,72,214411(2005).
[2] Sergei P., Eckhard S., Timo J., et al., Phys. Rev. B,76,012410(2007).
[3] Sawada H., Morikawa Y., Terakura K., et al., Phys. Rev. B,56,12154(1997).
[4] Huang Q., Santoro A., Lynn J. W., et al., Phys. Rev. B,55,14987(1997).
[5] Cussen E. J., Battle P. D., Chem. Mater.,12,831(2000).
[6] Christensen A. N., Ollivier G., J. Solid State Chem.,4,131(1972).
[7] Sacchett A., Baldini M., Crispold F., Phys. Rev. B,72,172407(2005).
[8] Daoud-Aladine A., Martin C., Phys. Rev. B,75,104417(2007).
[9] Belik A. A., Matsushita Y., Katsuya Y., et al., Phys. Rev. B,84,094438(2011).
[10] S nden R., St len S., Ravindran P., Phys. Rev. B,75,184105(2007).
[11] Benckiser, et al., Nature Mater.,10,189(2011).
[12] S nden R., Ravindran P., St len S., et al., Phys. Rev. B,74,144102(2006).
[1] Dagotto E., Science,309,257(2005).
[2] Heber J., Nature,459,28(2009).
[3] Ohotmo A., Muller D. A., Grazul J. L., Hwang H. Y., Nature,419,378(2002).
[4] Chen H. H., Kolpak A. M., Ismail-Beigi S., Adv. Mater.,22,2881(2010).
[5] Lin C. W., Okamoto S., Millis A. J., Phys. Rev. B,73, R041104(2006).
[6] Nanda B. R., Satpathy S., Phys. Rev. Lett,101,127201(2008).
[7] Smadici S., Abbamonte P., Bhattacharya A., et al., Phys. Rev. Lett,99,196404(2008).
[8] Bhattacharya A., May S. J., et al., Phys. Rev. Lett,100,257203(2008).
[9] May S. J., Shah A. B., Robertson J. L., et al., Phys. Rev. B,77,174409(2008).
[10] May S. J., Ryan P. J., Robertson J. L., et al., Nat. Mater.,8,892(2009).
[11] Tebano A., Aruta C., Sanna S., et al., Phys. Rev. Lett,100,137401(2008).
[12] Sadoc A., Mercey B., Simon C., et al., Phys. Rev. Lett,104,046804(2010).
[13] Muller D. A., Nakagawa N., Ohtomo A., et al., Nature,430,657(2004).
[14] Nakagawa N., Hwang H. Y., Muller D. A., Nat. Mater.,5,204(2006).
[15] Pentcheva R., Pickett W. E., Phys. Rev. B,74,035112(2006).
[16] Eckstein J. N., Nat. Mater.,6,473(2007).
[17] Chen H., Kolpak A. M., Ismail-Beigi S., Phys. Rev. B,79,161402(2009).
[18] Blochl P. E., Phys. Rev. B,50,17953(1994).
[19] Kresse G., Hafner J., Phys. Rev. B,47,558(1993).
[20] Kresse G., Hafner J., Phys. Rev. B,49,14251(1994).
[21] Kresse G., Furthmuller J., Comput. Mater. Sci.,6,15(1996).
[22] Kresse G., Joubert D., Phys. Rev. B,59,1758(1999).
[23] Dudarev S. L., Botton G. A., et al., Phys. Rev. B,57,1505(1998).
[24] Yin W. G., Volja D., Ku W., Phys. Rev. Lett,96,116405(2006).
[25] S nden R., Ravindran P., St len S., et al., Phys. Rev. B,74,144102(2006).
[26] Blochl P. E., Jepsen O., Andersen O. K., Phys. Rev. B,49,16223(1994).
[27] Fililppetti A., Pickett W. E., Phys. Rev. Lett,83,4184(1999).
[1] Zutic I., Fabian J., Das Sarma S., Rev. Mod. Phys.,76,323(2004).
[2] Wolf S A., Awschalom D. D., Buhrman R. A., et al., Science,294,1488(2001).
[3] Grünberg P. A., Rev. Mod. Phys.,80,1531(2008).
[4] Fert A., Rev. Mod. Phys.,80,1517(2008).
[5] Katsnelson M. I., Irkhin V. Y., et al., Rev. Mod. Phys.,80,315(2008).
[6] Son Y. W., Cohen M. L., Louie S. G., Nature,44,347(2006).
[7] Shen L., Yang S. S., et al., J. Am. Chem. Soc.,130,13956(2008).
[8] Zhou J., Sun Q., et al., J. Am. Chem. Soc.,133,15113(2011).
[9] Dagotto E., Science,318,1076(2007).
[10] Hwang H. Y., Science,313,1895(2006).
[11] Reiner J. W., Walker F. J., Ahn C. H., Science,323,1018(2009).
[12] Kawasaki M., Takahashi K., et al., Science,266,1540(1994).
[13] Koster G., Kropman B. L., et al., Appl. Phys. Lett.,73,2920(1998).
[14] Ohtomo A.,Hwang H. Y., Nature,427,423(2004).
[15] Nakagawa N., Hwang H. Y., Muller D. A., Nature Mater.,5,204(2006).
[16] Bell C., Harashima S., Hikita Y., et al., Appl. Phys. Lett.,94,222111(2009).
[17] Thiel S., Hammerl G., Schmehl A., et al., Science,313,1942(2006).
[18] Albina J. M., Mrovec M., Meyer B., et al., Phys. Rev. B,76,165103(2007).
[19] Gemming S., Seifert G., Acta Mater.,54,4299(2006).
[20] Park M. S., Rhim S. H., Freeman A. J., Phys. Rev. B,74,205416(2006).
[21] Bristowe N. C., Artacho E., Littlewood P. B., Phys. Rev. B,80,045425(2009).
[22] Brinkman A., Huijben M., Van Zalk M., et al., Nature Mater.,6,493(2007).
[23] Jang H. W., Felker D. A., Bark C. W., et al., Science,331,886(2011).
[24] Lin C. W., Millis A. J., Phys. Rev. B,78,184405(2008).
[25] Dong S., Yu R., Yunoki S., et al., Phys. Rev. B,78,201102(2008).
[26] Nanda B. R. K., Satpathy S., Phys. Rev. Lett,101,127201(2008).
[27] Nanda B. R. K., Satpathy S., Phys. Rev. B,79,054428(2010).
[28] Nanda B. R. K., Satpathy S., Phys. Rev. B,81,224408(2006).
[29] Smadici S., Abbamonte P., et al., Phys. Rev. Lett,99,196404(2007).
[30] Bhattacharya A., May S. J., et al., Phys. Rev. Lett,100,257203(2008).
[31] Koida T., Lippmaa M., Fukumura T., et al., Phys. Rev. B,66,144418(2002).
[32] May S. J., Shah A. B., et al., Phys. Rev. B,77,174409(2008).
[33] May S. J., Ryan P. J., Robertson J. L., et al., Nat. Mater.,8,892(2009).
[34] Perucchi A., Baldassarre L., Nucara A., et al., Nano Lett.,10,4819(2010).
[35] Nakamura M., Okuyama D., Lee J. S., et al., Adv. Mater.,21,1(2009).
[36] Kourkoutis L. F., et al., Proc. Natl. Acad. Sci. U.S.A.,107,1682(2010).
[37] Sadoc A., Mercey B., Simon C., et al., Phys. Rev. Lett,104,046804(2010).
[38] Zhai X., Mohapatra C. S., Shah A. B., et al., Adv. Mater.,22,1136(2010).
[39] Shah A. B., Ramasse Q. M., Zhai X., et al., Adv. Mater.,22,1156(2010).
[40] Garcia-Barriocanal J., Cezar J. C., et al., Nat. Commun.,1,1080(2010).
[41] Garcia-Barriocanal J., Bruno F. Y., et al., Adv. Mater.,22,627(2010).
[42] Wang Y., Niranjan M. K., Burton J. D., et al., Phys. Rev. B,79,212408(2009).
[43] Lee J., Sai N., Demkov A. A., et al., Phys. Rev. B,82,235305(2010).
[44] Burton J. D., Tsymbal E. Y., et al., Phys. Rev. Lett.,107,16601(2011).
[45] Chen H. H., Kolpak A. M., Ismail-Beigi S., et al., Adv. Mater.,22,2881(2010).
[46] Ahn C. H., Bhattacharya A., et al., Rev. Mod. Phys.,78,1185(2006).
[47] Bl chl P. E., Phys. Rev. B,50,17953(1994).
[48] Kress G., Furthmüller J., Comput. Mater. Sci,6,15(1996).
[49] Perdew J. P., Burke K., Ernzerhof M., Phys. Rev. Lett.,77,3865(1996).
[50] Dudarev S. L., Botton G. A., Savrasov S. Y., Phys. Rev. B,57,1505(1998).
[51] Sondena R., Ravindran P., Stolen S., et al., Phys. Rev. B,74,144102(2006).
[52] Lee J. H., Rabe K. M., Phys. Rev. Lett.,104,207204(2010).
[53] Yin W. G., Volja D., Ku W., Phys. Rev. Lett.,96,116405(2006).
[54] Luo W. D., Franceschetti A., et al., Phys. Rev. Lett.,99,036402(2007).
[55] Bl chl P. E., Jepsen O., Andersen O. K., Phys. Rev. B,49,16223(1994).
[56] Salamon M. B., Jaime M., et al., Rev. Mod. Phys.,73,585(2001).
[57] Dagotto E., et al., Phys. Rep.,344,1(2001).
[58] Tokura Y., et al., Phys. Rep.,69,797(2006).
[59] Zener C., et al., Phys. Rev.,82,403(1951).
[60] Hou F., Cai T. Y., Ju S., Shen M. R., Appl. Phys. Lett.,99,192510(2011).
[61] Fang Z., Solovyev I. V., Terakura K., Phys. Rev. Lett.,84,3169(2000).
[62] Rondinelli J. M., Spaldin N. A., Adv. Mater.,23,3363(2011).
[1] Ohtomo A.,Hwang H. Y., Nature,427,423(2004).
[2] Nakagawa N., Hwang H. Y., Muller D. A., Nature Mater.,5,204(2006).
[3] Bell C., Harashima S., Hikita Y., et al., Appl. Phys. Lett.,94,222111(2009).
[4] Thiel S., Hammerl G., Schmehl A., et al., Science,313,1942(2006).
[5] Bhattacharya A., May S. J., et al., Phys. Rev. Lett,100,257203(2008).
[6] Smadici S., Abbamonte P., et al., Phys. Rev. Lett,99,196404(2007).
[7] Bruno F Y, Garcia-Barriocanal J, et al., Phys. Rev. Lett,106,147205(2011).
[8] Wang L M, Lin J K, Shyu J P, et al., Phys. Rev. B,74,184412(2006).
[9] Garcia-Barriocanal J., Cezar J. C., et al., Nat. Commun.,1,1080(2010).
[10] Garcia-Barriocanal J., Bruno F. Y., et al., Adv. Mater.,22,627(2010).
[11] Choi W S, Jeong D W, Seo S S A, et al., Phys. Rev. B,83,195113(2011).
[12] Fang H., Tian-Yi C., Sheng J., Ming-Rong S., et al., ACS Nano,6,8552(2012).
[13] Bl chl P. E., Phys. Rev. B,50,17953(1994).
[14] Kresse G., Hafner J., Phys. Rev. B,47,558(1993).
[15] Kresse G., Hafner J., Phys. Rev. B,49,14251(1994).
[16] Kresse G., Furthmuller J., Comput. Mater. Sci.,6,15(1996).
[17] Kresse G., Joubert D., Phys. Rev. B,59,1758(1999).
[18] Bl chl P. E., Jepsen O., Andersen O. K., Phys. Rev. B,49,16223(1994).
[19] Hou F., Tian-Yi C., Sheng J., Ming-Rong S., Appl. Phys. Lett.,99,192510(2011)
[20] Yang K. Y., Zhu W. G., Xiao D., et al., Phys. Rev. B,84,201104(2011).
[21] Rüegg A., Mitra C., Demkov A., et al., Phys. Rev. B,85,245131(2012).
[22] Salamon M. B., Jaime M., et al., Rev. Mod. Phys.,73,585(2001).
[23] Dagotto E., et al., Phys. Rep.,344,1(2001).
[24] Tokura Y., et al., Phys. Rep.,69,797(2006).