Symmetrical interfacial reconstruction and magnetism in La${}_{0.7}{\mathrm{Ca}}_{0.3}{\mathrm{MnO}}_3/{\mathrm{YBa}}_2{\mathrm{Cu}}_3{\mathrm{O}}_7/{\mathrm{La}}_{0.7}{\mathrm{Ca}}_{0.3}{\mathrm{MnO}}_3$ heterostructures

We have analyzed the interface structure and composition of La${}_{0.7}$Ca${}_{0.3}$MnO${}_3$/YBa${}_2$Cu${}_3$O${}_7$/La${}_{0.7}$Ca${}_{0.3}$MnO${}_3$ trilayers by combined polarized neutron reflectometry, aberration-corrected microscopy, and atomic column resolution electron-energy-loss spectroscopy and x-ray absorption with polarization analysis. We find the same stacking sequence at both top and bottom cuprate interfaces. X-ray magnetic circular dichroism experiments show that both cuprate interfaces are magnetic with a magnetic moment induced in Cu atoms as expected from symmetric Mn-O-Cu superexchange paths. These results supply a solid footing for the applicability of recent theories explaining the interplay between magnetism and superconductivity in this system in terms of the induced Cu spin polarization at both interfaces [J. Salafranca and S. Okamoto, Phys. Rev. Lett. 105, 256804 (2010)].

Figure 1

(a) Non-spin-flip reflectivity of neutrons polarized parallel to the applied field ($R^{++}$) and antiparallel ($R^{--}$) to the applied field, measured at 9.5 K at the indicated fields after zero-field cooling. Spin-flip reflectivities, not shown, were zero indicating the magnetizations were collinear to the applied fields. Black lines are fits to the data. Reflectivities for H = 335 Oe are reduced by a factor of 100 for clarity. Inset: XR data taken at room temperature. The black line is the fit to the data. (b) Neutron (nuclear and magnetic) and x-ray SLD depth profiles obtained from the fits to the neutron and x-ray data, respectively. The data at H = 186 and 335 Oe were taken successively, after applying a negative saturating field of H = −5.54 kOe. The field was applied along the [100] direction.

Figure 2

XRMS and TEY XMCD spectra at the Mn absorption edge [(a) and (b)] and at the Cu absorption edge [(c) and (d)] at 30 K.

Figure 3

X-ray magnetic reflectivity loops taken at $L_3$ Mn (a) and Cu (b) absorption edges at 30 K applying the field along [100] (red solid line) and [110] (black open symbols).

Figure 4

(a) High-resolution image of a LCMO/YBCO/LCMO trilayer. EELS elemental maps using normalized integrated intensities for the O K (b), Mn $L_{2,3}$ (c), Ba $M_{4,5}$ (d), and La $M_{4,5}$ (e). The maps were produced by subtracting the background using a power-law fit and then integrating the remaining intensity under the edge over windows 30 eV wide. The acquisition time was 0.03 s per pixel. The color map of panel (f) has been produced by overlaying the Ba image (blue/dark gray) and the Mn image (red/gray), and the La image (green/light gray). The scale bar in all cases represents 2 nm.