tailieunhanh - Magnetism in the interfaces of the sandwiched PbTiO3/LaAlO3/SrTiO3 hetero-structure

We investigate the effect of PbTiO3 on the LaAlO3/SrTiO3 hetero-structure by density functional theory, where the asymmetry sandwich not only forms a quasi-two dimensional electron gas but also reveals a ferromagnetic state in the TiO2 interfaces. It is found out that magnetic moments of TiO2 interface layers are around µB while they are mostly negligible in the pure LaAlO3/SrTiO3 system. Even though magnetic moments are mainly produced by Ti t2g orbitals, oxygen plays a key role in the formation of the ferromagnetic state since polar distortions primarily occur in oxygen positions of the SrTiO3 and PbTiO3 sides in opposite directions. | Communications in Physics, Vol. 25, No. 3 (2015), pp. 219-225 DOI: MAGNETISM IN THE INTERFACES OF THE SANDWICHED PbTiO3 /LaAlO3 /SrTiO3 HETERO-STRUCTURE BACH HUONG GIANG, NGUYEN THUY TRANG, TRAN VAN NAM, AND BACH THANH CONG Computational Material Science Lab, Faculty of Physics, Hanoi University of Science, Vietnam National University, 334 Nguyen Trai, Thanh Xuan, Hanoi, Vietnam E-mail: gianghuongbach@ Received 05 September 2014 Accepted for publication 24 April 2015 Abstract. We investigate the effect of PbTiO3 on the LaAlO3 /SrTiO3 hetero-structure by density functional theory, where the asymmetry sandwich not only forms a quasi-two dimensional electron gas but also reveals a ferromagnetic state in the TiO2 interfaces. It is found out that magnetic moments of TiO2 interface layers are around µB while they are mostly negligible in the pure LaAlO3 /SrTiO3 system. Even though magnetic moments are mainly produced by Ti t2g orbitals, oxygen plays a key role in the formation of the ferromagnetic state since polar distortions primarily occur in oxygen positions of the SrTiO3 and PbTiO3 sides in opposite directions. Keywords: magnetism, LaAlO3 /SrTiO3 , PbTiO3 /LaAlO3 /SrTiO3 . I. INTRODUCTION The interface between perovskite structure material has recently exposed various interesting properties, which are completely different than the bulk systems. While LaAlO3 (LAO) and SrTiO3 (STO) bulks are both well-known as insulators, an existence of metallic phase has been found on LAO/STO interface. Whether termination layer is SrO or TiO2 , the interface will be insulator or metal with an extremely high mobility [1]. It is generally believed that free carriers are injected in the interface in order to overcome the “polar catastrophe” [2,3] causing by the polar discontinuity between two perovskites. In addition, a ferromagnetic order and a superconductivitylike phase has been observed co-existentially under a specific temperature and