Appearance and disappearance of ferromagnetism in ultrathin LaMnO3 on SrTiO3 substrate: A viewpoint from first principles

作者：An, Ming; Weng, Yakui; Zhang, Huimin; Zhang, Jun-Jie; Zhang, Yang; Dong, Shuai^*

来源：Physical Review B, 2017, 96(23): 235112.

DOI：10.1103/PhysRevB.96.235112

• GENERALIZED GRADIENT APPROXIMATION
• MAGNETIC-PROPERTIES
• ELECTRONIC-STRUCTURE
• NEUTRON-DIFFRACTION
• OXIDE
• INTERFACES
• PHYSICS
• TRANSITION
• MAGNETOTRANSPORT
• EXCHANGE

The intrinsic magnetic state (ferromagnetic or antiferromagnetic) of ultrathin LaMnO3 films on the most commonly used SrTiO3 substrate is a long-existing question under debate. Either strain effect or nonstoichiometry was argued to be responsible for the experimental ferromagnetism. In a recent experiment [X.R. Wang, C.J.Li, W.M. Lu, T.R. Paudel, D.P. Leusink, M.Hoek, N.Poccia, A.Vailionis, T.Venkatesan, J.M.D. Coey, E.Y. Tsymbal, Ariando, and H. Hilgenkamp, Science 349, 716 (2015)], one more mechanism, namely, the self-doping due to polar discontinuity, was argued to be the driving force of ferromagnetism beyond the critical thickness. Here systematic first-principles calculations have been performed to check these mechanisms in ultrathin LaMnO3 films as well as superlattices. Starting from the very precise descriptions of both LaMnO3 and SrTiO3, it is found that the compressive strain is the dominant force for the appearance of ferromagnetism, while the open surface with oxygen vacancies leads to the suppression of ferromagnetism. Within LaMnO3 layers, the charge reconstructions involve many competitive factors and certainly go beyond the intuitive polar catastrophe model established for LaAlO3/SrTiO3 heterostructures. Our paper not only explains the long-term puzzle regarding the magnetism of ultrathin LaMnO3 films but also sheds light on how to overcome the notorious magnetic dead layer in ultrathin manganites.

• 出版日期2017-12-11
• 单位东南大学