FULL PAPER © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim (1 of 7) 1600547 wileyonlinelibrary.com Oxygen Vacancy Dependence of Magnetic Behavior in the LaAlO 3 /SrTiO 3 Heterostructures Hai-Long Hu, Lei Ao, Anh Pham, Danyang Wang,* Yu Wang, Zhigang Chen, Charlie Kong, Thiam Teck Tan, Xiaotao Zu, and Sean Li* H.-L. Hu, L. Ao, Dr. A. Pham, Dr. D. Wang, Dr. T. T. Tan, Prof. S. Li School of Materials Science and Engineering University of New South Wales Sydney, New South Wales 2052, Australia E-mail: dy.wang@unsw.edu.au; sean.li@unsw.edu.au L. Ao, Prof. X. Zu School of Physical Electronics University of Electronic Science and Technology of China Chengdu 610054, China Dr. Y. Wang, Dr. C. Kong Mark Wainwright Analytical Centre University of New South Wales Sydney, New South Wales 2052, Australia Dr. Z. Chen School of Mechanical and Mining Engineering University of Queensland Brisbane, Queensland 4072, Australia DOI: 10.1002/admi.201600547 AlO 2 layers and the build-up of triplet cou- pling of Ti 3d states through oxygen bonds (or possibly vacancies) in the TiO 2 interface plane may be responsible for the observed magnetism. [7] Theoretical calculation sug- gests that the robust ferromagnetism is not the intrinsic property of LAO/STO interface and the oxygen vacancy in STO or LAO layer is the origin of ferromagnetism. [7] In fact, the formation and distribution of oxygen vacancies in LAO/STO have been considered to play a critical role in deter- mining the novel physical phenomena appearing in LAO/STO heterostructures, but the mechanism of the oxygen vacancy effects on the magnetic behaviors of LAO/STO is still unclear. Up to date, there is no universal explanation on the origin of ferromagnetism occurring in LAO/STO heterostructures. A systematic experimental verification for the role of oxygen vacancy on the introduction of magnetic state in LAO/STO het- erostructures is eagerly awaited. In this work, we experimen- tally and theoretically demonstrate that the enhancement of the saturated magnetization of the LAO/STO heterostructures was closely related to the increased density of oxygen vacancies in this particular materials system. 2. Results and Discussions As shown in Figure 1a, the strong reflection high energy electron diffraction (RHEED) intensity oscillations are maintained up to 24 oscillations (corresponding to a thickness of ≈9.1 nm), sug- gesting a layer-by-layer growing mode for our samples. Figure 1b shows the AFM topographic images of the as-deposited 24 unit cells (uc) LAO thin films with the typical step-flow terrace. The average surface roughness value (R a ) is ≈0.283 nm for the films grown under the oxygen partial pressure of 5 × 10 -8 Torr, sug- gesting the good surface quality in such a low oxygen processing pressure. Figure 1c shows the XRD θ-2θ scan spectra of 24 uc LAO thin films grown under different oxygen partial pressures. Only the strong (00l) reflections are detected, indicating all the films are highly c-axis oriented. X-ray diffraction (XRD) reciprocal space mapping (RSM) was performed on the sample prepared under the oxygen partial pressure of 5 × 10 -8 Torr. Figure 1d,e shows the RSM around the (003) and (203) reflections, respec- tively. The diffraction peak of the LAO film locates right above that of the substrate as arrowed, i.e., the in-plane lattice parameter of the film is almost the same as that of the substrate, indicating the The discovery of magnetism at the LaAlO 3 /SrTiO 3 heterostructures has attracted a lot of interests in regards to the origin of magnetic properties appearing in this nonmagnetic system. In this paper, the existence of a robust ferromagnetic state in the LaAlO 3 /SrTiO 3 heterostructures is demonstrated. The oxygen vacancy dependence of magnetic phenomena demonstrates the correlation between the magnetic properties and the oxygen vacancies. The strong ferromagnetism can be also manipulated by controlling the partial pressure of oxygen during the film deposition process. The well-controlled magnetism may open an avenue for the applications of magnetic storage and spintronics with the LaAlO 3 /SrTiO 3 heterostructures. 1. Introduction Magnetic properties induced by interface engineering of two nonmagnetic SrTiO 3 (STO) and LaALO 3 (LAO) materials have been intensively studied due to their promising applications in all oxide-based spintronics. [1–3] However, the origin of the emerging magnetisms in the correlated interface is complicated. It is argued that the magnetism is associated with the generation of Ti 3+ ions, [4] which is due to the occupation of low energy Ti-d xy - like subbands induced by the interfacial splitting of orbital degen- eracy or interfacial disorder. [5] Electronic reconstruction within the polar catastrophe and atomic reconstruction with chemical defects were also suggested. [6] Some experimental results show the magnetic moments induced by the oxygen vacancies at Adv. Mater. Interfaces 2016, 1600547 www.advmatinterfaces.de www.MaterialsViews.com