X-ray absorption spectroscopy study of the electronic and magnetic proximity effects in ${\mathrm{YBa}}_2{\mathrm{Cu}}_3{\mathrm{O}}_7/{\mathrm{La}}_{2/3}{\mathrm{Ca}}_{1/3}{\mathrm{MnO}}_3$ and ${\mathrm{La}}_{2-x}{\mathrm{Sr}}_x{\mathrm{CuO}}_4/{\mathrm{La}}_{2/3}{\mathrm{Ca}}_{1/3}{\mathrm{MnO}}_3$ multilayers

With x-ray absorption spectroscopy we investigated the orbital reconstruction and the induced ferromagnetic moment of the interfacial Cu atoms in ${\mathrm{YBa}}_2{\mathrm{Cu}}_3{\mathrm{O}}_7/{\mathrm{La}}_{2/3}{\mathrm{Ca}}_{1/3}{\mathrm{MnO}}_3$ (YBCO/LCMO) and ${\mathrm{La}}_{2-x}{\mathrm{Sr}}_x{\mathrm{CuO}}_4/{\mathrm{La}}_{2/3}{\mathrm{Ca}}_{1/3}{\mathrm{MnO}}_3$ (LSCO/LCMO) multilayers. We demonstrate that these electronic and magnetic proximity effects are coupled and are common to these cuprate/manganite multilayers. Moreover, we show that they are closely linked to a specific interface termination with a direct Cu-O-Mn bond. We furthermore show that the intrinsic hole doping of the cuprate layers and the local strain due to the lattice mismatch between the cuprate and manganite layers are not of primary importance. These findings underline the central role of the covalent bonding at the cuprate/manganite interface in defining the spin-electronic properties.

Figure 1

XAS curves at the $\mathrm{Cu}-L_{3,2}$ edge of YBCO/LCMO taken at 2 K. (a) XAS data for linear polarization in FY mode. (b) Close-up of the $L_3$ edge. Data (points) are shown together with the fit (thick lines) using four Lorentzian functions (thin lines) and a background with a linear and a sigmoid function (thin black line). The XLD of each peak is indicated by the patterns. (c) and (d) Corresponding XAS data for linear polarization in TEY mode. (e) XAS and XMCD data for circular polarization in FY mode. (f) Close-up of the $L_3$ edge shown with the same symbols as in (b). Also shown is the fit of the XMCD signal (black line). (g) and (h) Corresponding XAS and XMCD data for circular polarization in TEY mode.

Figure 2

XAS curves at the $\mathrm{Cu}-L_{3,2}$ edge of LSCO/LCMO 9_BL at 2 K shown with the same symbols as in Fig. 1.

Figure 3

XAS curves at the $\mathrm{Cu}-L_{3,2}$ edge of LSCO/LCMO 3_BL at 2 K in the TEY mode shown with the same symbols as in Fig. 1. Inset of (a): sketch of the different LSCO/LCMO interface terminations. The bottom interface exemplifies the direct $\mathrm{Cu}-{\mathrm{O}}^{\mathrm{ap}}-\mathrm{Mn}$ bond, the top one displays the zigzag-type $\mathrm{Cu}-{\mathrm{O}}^{\mathrm{ap}}-\mathrm{La}-{\mathrm{O}}^{\mathrm{ap}}-\mathrm{Mn}$ bond.

Figure 4

Illustration of the procedure for the background subtraction to obtain the resonant absorption at the $\mathrm{Cu}-L_{3,2}$ edges in TEY [(a), (b), and (c)] and FY [(d), (e), and (f)] mode. (a) and (b) show the raw data of the total electron and fluorescence yield for a series of three consecutive series of measurements at positive and negative helicity that were performed at 0.5 T and 2 K. (b) and (e) display the same data after the normalization with respect to the intensity in the pre-edge region. The black line shows the extrapolation of the linear fit of the pre-edge region that is used to account for the background absorption. (c) and (f) show the absorption at the $\mathrm{Cu}-L_{3,2}$ edges obtained after the subtraction of this linear background.