$\mathrm{La}_{\mathrm{1-}x} \mathrm{Mn}_{\mathrm{1-}y} \mathrm{O}_{\mathrm{1\pm}\delta}$ buffer layers on inclined substrate deposited MgO templates for coated conductors

TL;DR

This study demonstrates the successful deposition of LaMnO3 buffer layers on inclined substrate MgO templates, optimizing growth conditions to enhance the critical current density of subsequent superconducting films for coated conductor applications.

Contribution

It introduces a systematic method for depositing high-quality LaMnO3 buffer layers on inclined MgO substrates, improving superconducting film performance in coated conductors.

Findings

LaMnO3 buffer layers can be grown without surface outgrowths at high growth rates.

Single-phase LaMnO3 films are achievable below 775°C and at specific oxygen pressures.

Superconducting films on LaMnO3 buffers exhibit up to 30% higher critical current density.

Abstract

Most commercial high-temperature superconducting coated conductors based on ion beam assisted MgO deposited templates use $\mathrm{LaMnO_3}$ (LMO) films as the terminating buffer layer. In contrast, coated conductors based on inclined substrate deposition (ISD)-MgO technology are still produced with homoepitaxial (homoepi)-MgO as the cap layer. In this work we report on the deposition of LMO buffer layers on ISD-MgO/homoepi-MgO by electron beam physical vapor deposition. The growth parameters of textured LMO films were studied systematically and their properties were optimized regarding the critical current densitiy ($J_\mathrm{c}$) of the subsequently deposited $\mathrm{DyBa_2Cu_3O}_{\mathrm{7-}\delta}$ (DyBCO) superconducting films. LMO films without outgrowths at the surface were obtained at growth rates of up to $4\,\mathrm{\r{A}/s}$. Despite the formation of non-stoichiometric LMO films containing $59\,\%$ La, single-phase films were obtained at substrate temperatures below $775^{\circ}\mathrm{C}$ and at oxygen partial pressures of up to $4\times10^{-4}\,\mathrm{mbar}$ due to a large homogeneity region towards La. The $J_\mathrm{c}$ values of DyBCO films deposited on LMO were found to be independent of the LMO thickness in a range from $50\,\mathrm{nm}$ to $450\,\mathrm{nm}$. DyBCO films on LMO reach $J_\mathrm{c}=0.83\,\mathrm{MA/cm^2}$ at $77\,\mathrm{K}$ in zero applied field. This value is up to $30\,\%$ higher than those of DyBCO films grown directly on homoepi-MgO. The wide range of LMO growth parameters and higher $J_\mathrm{c}$ values of DyBCO on LMO compared to DyBCO on homoepi-MgO make this material attractive for its use in manufacturing coated conductors based on ISD-MgO technology.