Structural, magnetic, and superconducting properties of pulsed-laser-deposition-grown La_1.85Sr_0.15CuO_4/La_2/3Ca_1/3MnO_3 superlattices on (001)-oriented LaSrAlO_4 substrates

Abstract

Epitaxial La_1.85Sr_0.15CuO4/La_2/3Ca_1/3MnO_3 (LSCO/LCMO) superlattices on (001)-oriented LaSrAlO_4 substrates have been grown with pulsed laser deposition technique. Their structural, magnetic, and superconducting properties have been determined with in situ reflection high-energy electron ffraction, x-ray diffraction, specular neutron reflectometry, scanning transmission electron microscopy, electric transport, and magnetization measurements. We find that despite the large mismatch between the in-plane lattice parameters of LSCO (a = 0.3779 nm) and LCMO (a = 0.387 nm) these superlattices can be grown epitaxially and with a highcrystalline quality. While the first LSCO layer remains clamped to the LaSrAlO4 substrate, a sizable strain relaxation occurs already in the first LCMO layer. The following LSCO and LCMO layers adopt a nearly balanced state in which the tensile and compressive strain effects yield alternating in-plane lattice parameters with an almost constant average value. No major defects are observed in the LSCO layers, while a significant number of vertical antiphase boundaries are found in the LCMO layers. The LSCO layers remain superconducting with a relatively high superconducting onset temperature of T onset c ≈ 36 K. The macroscopic superconducting response is also evident in the magnetization data due to a weak diamagnetic signal below 10 K for H ab and a sizable paramagnetic shift for H c that can be explained in terms of a vortex-pinning-induced flux compression. The LCMO layers maintain a strongly ferromagnetic state with a Curie temperature of T Curie ≈ 190 K and a large low-temperature saturation moment of about 3.5(1) μB per Mn ion. These results suggest that the LSCO/LCMO superlattices can be used to study the interaction between the antagonistic ferromagnetic and uperconducting orders and, in combination with previous studies on YBa_2Cu_3O_7−x /La_2/3Ca_1/3MnO_3 superlattices, may allow one to identify the relevant mechanisms.