Structural, magnetic, and superconducting properties of pulsed-laser-deposition-grownLa1.85Sr0.15CuO4/La2/3Ca1/3MnO3superlattices on (001)-orientedLaSrAlO4substrates

Abstract

Epitaxial ${\mathrm{La}}_{1.85}{\mathrm{Sr}}_{0.15}{\mathrm{CuO}}_{4}/{\mathrm{La}}_{2/3}{\mathrm{Ca}}_{1/3}{\mathrm{MnO}}_{3}$ (LSCO/LCMO) superlattices on $(001)$-oriented ${\mathrm{LaSrAlO}}_{4}$ 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 diffraction, 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 high crystalline quality. While the first LSCO layer remains clamped to the ${\mathrm{LaSrAlO}}_{4}$ 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 ${T}_{c}^{\text{onset}}\ensuremath{\approx}36$ K. The macroscopic superconducting response is also evident in the magnetization data due to a weak diamagnetic signal below 10 K for $H$ $\ensuremath{\parallel}$ $ab$ and a sizable paramagnetic shift for $H$ $\ensuremath{\parallel}$ $c$ 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 ${T}^{\text{Curie}}\ensuremath{\approx}190$ K and a large low-temperature saturation moment of about 3.5(1) ${\ensuremath{\mu}}_{B}$ per Mn ion. These results suggest that the LSCO/LCMO superlattices can be used to study the interaction between the antagonistic ferromagnetic and superconducting orders and, in combination with previous studies on ${\text{YBa}}_{2}{\text{Cu}}_{3}{\text{O}}_{7\ensuremath{-}x}/{\text{La}}_{2/3}{\text{Ca}}_{1/3}{\text{MnO}}_{3}$ superlattices, may allow one to identify the relevant mechanisms.