Magnetic Proximity Effect in ${\mathrm{YBa}}_2{\mathrm{Cu}}_3{\mathrm{O}}_7/{\mathrm{La}}_{2/3}{\mathrm{Ca}}_{1/3}{\mathrm{MnO}}_3$ and ${\mathrm{YBa}}_2{\mathrm{Cu}}_3{\mathrm{O}}_7/{\mathrm{LaMnO}}_{3\mathbf{+}\delta }$ Superlattices

Using neutron reflectometry and resonant x-ray techniques we studied the magnetic proximity effect (MPE) in superlattices composed of superconducting ${\mathrm{YBa}}_2{\mathrm{Cu}}_3{\mathrm{O}}_7$ and ferromagnetic-metallic ${\mathrm{La}}_{0.67}{\mathrm{Ca}}_{0.33}{\mathrm{MnO}}_3$ or ferromagnetic-insulating ${\mathrm{LaMnO}}_{3+\delta }$. We find that the MPE strongly depends on the electronic state of the manganite layers, being pronounced for the ferromagnetic-metallic ${\mathrm{La}}_{0.67}{\mathrm{Ca}}_{0.33}{\mathrm{MnO}}_3$ and almost absent for ferromagnetic-insulating ${\mathrm{LaMnO}}_{3+\delta }$. We also detail the change of the magnetic depth profile due to the MPE and provide evidence for its intrinsic nature.

Figure 1

PNR curves for spin-up ($|+⟩$) and spin-down ($|-⟩$) polarization of (a) $[\mathrm{YBCO}(10\mathrm{nm})/\mathrm{LMO}(10\mathrm{nm}){]}_{10}$ and (c) $[\mathrm{YBCO}(10\mathrm{nm})/\mathrm{LCMO}(10\mathrm{nm}){]}_{10}$. Also shown are unpolarized curves at 300 K. Arrows mark the position of the SLBPs. The curves are vertically shifted for clarity. (b) and (d): Depth profiles as obtained from fitting the data in (a) and (c) (solid lines) of the nuclear (green line) and magnetic (red line) scattering length densities (SLD) which are proportional to the nuclear and magnetic potentials, respectively. Arrows point along the SL growth direction. The error for the SLD in (b) and (d) is smaller than the line thickness; all the error bars in these two figures were obtained as described in Ref. 22.

Figure 2

(a) $T$ dependence of the asymmetry between the peak intensities of the spin-down and spin-up polarized curves at the 3rd order SLBP showing an anomalous order-parameter-like increase below $T_c$. Inset: Magnification around this peak above and well below $T_c$. (b) Corresponding changes of the magnetic depth profile.

Figure 3

XMCD spectra in TEY mode at the $L$ edges of Mn and Cu plotted in terms of the dichroism, $I^{+}-I^{-}$, for (a) YBCO/LCMO and (b) YBCO/LMO. Inset: Corresponding normalized x-ray absorption spectra.

Figure 4

(a) Resonant x-ray reflectometry curve at the Cu $L_3$ edge of YBCO/LCMO obtained at 300 K. (b) Difference curve between positive and negative x-ray helicity at 40 K containing the information about the depth profile of the FM Cu moments. The simulations have been performed for the cases where the Cu moments reside in the YBCO layers (red line) and the LCMO layers (green dashed line), respectively.