Study of equilibrium carrier transfer in LaAlO₃/SrTiO₃ from an epitaxial La_1−x Sr _x MnO₃ ferromagnetic layer

Abstract

Using x-ray magnetic circular dichroism and ab-initio calculations, we explore the La 1−x Sr x MnO 3 /LaAlO 3 /SrTiO 3 (001) heterostructure as a mean to induce transfer of spin polarized carriers from ferromagnetic La 1−x Sr x MnO 3 layer into the 2DEG (two-dimensional electron gas) at the LaAlO 3 /SrTiO 3 interface. By out-of-plane transport measurements, the tunneling across the LaAlO 3 barrier is also analyzed. Our results suggest small or vanishing spin-polarization for the 2DEG: magnetic dichroism does not reveal a neat signal on Ti atoms, while calculations predict, for the pristine stoichiometric interface, a small spin-resolved mobile charge of 2.5×10 13 cm −2 corresponding to a magnetic moment of 0.038 μ B per Ti atom, tightly confined within the single SrTiO 3 layer adjacent to LaAlO 3 . Such a small magnetization is hard to be detected experimentally and perhaps not robust enough to survive to structural disorder, native doping, or La 1−x Sr x MnO 3 dead-layer effects. Our analysis suggests that, while some spin-diffusion cannot be completely ruled out, the use of ferromagnetic La 1−x Sr x MnO 3 epilayers grown on-top of LaAlO 3 /SrTiO 3 is not effective enough to induce robust spin-transport properties in the 2DEG. The examined heterostructure is nevertheless an excellent test-case to understand some fundamental aspects of the spin-polarized charge transfer in 2D wells.

Oxide spin-orbitronics: spin-charge interconversion and topological spin textures

“…Additionally to the gate voltage, a control of the conversion might be obtained using strain 63 . Beyond these spin-pumping experiments, attempts have also been made to detect the conversion using electrical spin injection from LSMO to the LAO/STO 2DEG 64 .…”

Spin-Hall current and nonlocal transport in ferromagnet-free multiband models for SrTiO3 -based nanodevices in the presence of impurities

“…Recently, spintronics, a branch of electronics based on the manipulation of electron spin, rather than the charge, is emerging as a promising technology for information storing and processing, and for sensing [1][2][3]. Spin injection in spintronic devices can be done by using ferromagnetic leads, however, the efficiency of this process is usually low [4][5][6]. An alternative approach is to use semiconducting materials characterized by large charge-to-spin conversion efficiency.…”