Superconductivity-driven negative interfacial magnetization in YBa2Cu3O7−δ/SrTiO3/La0.67Sr0.33MnO3 heterostructures

Abstract

Using spin-polarized neutron reflectivity experiments, we demonstrate an unusual proximity behavior when a superconductor (SC) and a ferromagnet (FM) are coupled through an insulator (I) in YBa2Cu3O7−δ (SC)/SrTiO3 (I)/La0.67Sr0.33MnO3 (FM) heterostructures. We have observed an unexpected magnetic reversal confined to the interface region of the FM below the superconducting transition temperature. The magnetization of the interfacial FM layer at the I/FM interface was found to be aligned opposite to the magnetization of the rest of the FM layer. This result indicates that the Cooper pairs tunnel across the insulator, interact with the local magnetization in the interfacial region (extending ∼30 Å) of the FM, and then modify the magnetization at the interface. This unexpected magnetic behavior cannot be explained on the basis of the existing theoretical models. However, the length scale associated here clearly suggests the long-range proximity effect as a result of tunneling of Cooper pairs. The magnetic exchange field-effect across SC/I/FM interfaces driven by tunneling may serve as the basis for application in superconducting spintronic devices.

Correlation of Magnetic and Superconducting Properties with the Strength of the Magnetic Proximity Effect in La0.67Sr0.33MnO3/SrTiO3/YBa2Cu3O7−δ Heterostructures

“…We observed significantly higher T sc ∼ 86 K for the YBCO layer in both S1 and S2 as compared to those of heterostructures S3 and S4 (∼65 K). 8 The increase in T sc of YBCO in the present case may be due to a reduction in the lattice parameter c, which is consistent with earlier reports. 25 A significant reduction in the T sc of the YBCO film in the heterostructure S4 has also been observed due to an increase of the lattice parameter (c) upon ion irradiation.…”

“…We observe a smaller out-of-plane lattice parameter for YBCO as compared to that found in the heterostructures S3 and S4 (∼11.68 Å). 8 The change in the atomic structure (i.e., reduction/increase in the lattice parameter) is directly correlated with the SC properties of YBCO. 24 A strong suppression in the T sc of YBCO has also been observed in the irradiated MgO(substrate)/YBCO/STO/LSMO trilayer and MgO(substrate)/YBCO/LSMO bilayer (reverse stacking sequence), which was attributed to an increase (∼11.88 Å) in the lattice parameter upon ion irradiation.…”

“…The deposition parameters for growth of these heterostructures were kept similar to those used for growing the heterostructures MgO-(substrate)/YBCO/LSMO and MgO(substrate)/YBCO/STO/ LSMO with a reverse stacking sequence, henceforth known as S3 and S4, studied earlier. 8 The structural characterization of the heterostructures was carried out by X-ray diffraction (XRD) and X-ray reflectivity (XRR) techniques using Cu Kα radiation from a rotating anode X-ray source. Specular XRR provides the depth-dependent electron scattering length density (ESLD) profile, which determines the depth-dependent layered structure of heterostructures and yield parameters such as the layer thickness, density, and interface roughness of each layer in the heterostructure.…”

“…We observe that T sc of YBCO and magnetization of LSMO layers are higher compared to those of similarly grown systems but with a reverse stacking sequence of layers, that is, YBCO/LSMO and YBCO/STO/LSMO. 8 The analysis of low- temperature PNR data below the T sc of these heterostructures shows the emergence of an MD region of about 20 and 15 Å, respectively, in the LSMO layer near the interface for the bilayer and trilayer, respectively. These values of MD regions in the interfacial LSMO layer are smaller than the ones obtained for the system with a reverse layer sequence in proximity (bilayer) geometry (∼60 Å) and tunnelling (trilayer) geometry (∼25 Å).…”

“…These values of MD regions in the interfacial LSMO layer are smaller than the ones obtained for the system with a reverse layer sequence in proximity (bilayer) geometry (∼60 Å) and tunnelling (trilayer) geometry (∼25 Å). 8 In addition, to understand the effect of SC and magnetic properties on the strength of MPE in these oxide heterostructures, the results from different LSMO and LCMObased FM/SC and FM/I/SC systems, studied by different groups, were also compared. Observation of MPE in these heterostructures with different layer constituents and configurations establishes that it is an intrinsic interfacial phenomenon in these oxide systems.…”