Pulsed laser deposition growth of heteroepitaxial YBa_(2)Cu_(3)O_(7)/La_(0.67)Ca_(0.33)MnO_(3) superlattices on NdGaO_(3) and Sr_(0.7)La_(0.3)Al_(0.65)Ta_(0.35)O_(3) substrates

Abstract

Heteroepitaxial superlattices of [YBa_(2)Cu_(3)O_(7)(n)/La_(0.67)Ca_(0.33)MnO_(3)(m)]_(x) (YBCO/LCMO), where n and m are the number of YBCO and LCMO monolayers and x the number of bilayer repetitions, have been grown with pulsed laser deposition on NdGaO_(3) (110) and Sr_(0.7)La_(0.3)Al_(0.65)Ta_(0.35)O_(3) (001). These substrates are well lattice matched with YBCO and LCMO and, unlike the commonly used SrTiO_(3), they do not give rise to complex and uncontrolled strain effects at low temperature. The growth dynamics and the structure have been studied in situ with reflection high-energy electron diffraction and ex situ with scanning transmission electron microscopy, x-ray diffraction, and neutron reflectometry. The individual layers are found to be flat and continuous over long lateral distances with sharp and coherent interfaces and with a well-defined thickness of the individual layer. The only visible defects are antiphase boundaries in the YBCO layers that originate from perovskite unit-cell height steps at the interfaces with the LCMO layers. We also find that the first YBCO monolayer at the interface with LCMO has an unusual growth dynamics and is lacking the CuO chain layer, while the subsequent YBCO layers have the regular Y-123 structure. Accordingly, the CuO_(2) bilayers at both the LCMO/YBCO and the YBCO/LCMO interfaces are lacking one of their neighboring CuO chain layers and, thus, half of their hole-doping reservoir. Nevertheless, from electric transport measurements on a superlattice with n=2 we obtain evidence that the interfacial CuO_(2) bilayers remain conducting and even exhibit the onset of a superconducting transition at very low temperature. Finally, we show from dc magnetization and neutron reflectometry measurements that the LCMO layers are strongly ferromagnetic.