Superconducting and normal-state interlayer-exchange-coupling in La$_{0.67}$Sr$_{0.33}$MnO${3}$-YBa$_{2}$Cu$_{3}$O$_{7}-La$_{0.67}$Sr$_{0.33}$ MnO${3}$ epitaxial trilayers

TL;DR

This study investigates interlayer exchange coupling in LSMO-YBCO-LSMO trilayers, revealing predominantly antiferromagnetic coupling that persists through superconductivity, with coupling strength influenced by temperature and layer thickness, consistent with tunneling transport models.

Contribution

It provides the first detailed analysis of interlayer exchange coupling in magnetic-superconductor multilayers, showing how superconductivity affects coupling energy and its dependence on layer thickness and temperature.

Findings

Antiferromagnetic exchange coupling persists in both normal and superconducting states.

Coupling energy grows on cooling and truncates below T_c.

Coupling strength decreases exponentially with YBCO layer thickness.

Abstract

The issue of interlayer exchange coupling in magnetic multilayers with superconducting (SC) spacer is addressed in La$_{0.67}$Sr$_{0.33}$MnO$_{3}$ (LSMO) - YBa$_{2}$Cu$_{3}$O$_{7}$ (YBCO) - La$_{0.67}$Sr$_{0.33}$MnO$_{3}$ (LSMO) epitaxial trilayers through resistivity, ac-susceptibility and magnetization measurements. The ferromagnetic (FM) LSMO layers possessing in-plane magnetization suppress the critical temperature (T$_{c})$ of the c-axis oriented YBCO thin film spacer. The superconducting order, however, survives even in very thin layers (thickness d$_{Y} \sim $ 50 {\AA}, $\sim $ 4 unit cells) at T $<$ 25 K. A predominantly antiferromagnetic (AF) exchange coupling between the moments of the LSMO layers at fields $<$ 200 Oe is seen in the normal as well as the superconducting states of the YBCO spacer. The exchange energy J$_{1}$ ($\sim $ 0.08 erg/cm$^{2}$ at 150 K for d$_{Y}$ = 75 {\AA}) grows on cooling down to T$_{c}$, followed by truncation of this growth on entering the superconducting state. The coupling energy J$_{1}$ at a fixed temperature drops exponentially with the thickness of the YBCO layer. The temperature and d$_{Y}$ dependencies of this primarily non-oscillatory J$_{1}$ are consistent with the coupling theories for systems in which transport is controlled by tunneling. The truncation of the monotonic T dependence of J$_{1}$ below T$_{c}$ suggests inhibition of single electron tunneling across the CuO$_{2}$ planes as the in-plane gap parameter acquires a non-zero value.