Measurement of Magnetic Exchange in Ferromagnet-Superconductor La2/3Ca1/3MnO3/YBa2Cu3O7 Bilayers
S. R. Giblin, J. W. Taylor, J. A. Duffy, M. W. Butchers, C. Utfeld, S., B. Dugdale, T. Nakamura, C. Visani, and J. Santamaria
TL;DR
This study directly measures magnetic correlations in the normal state of a high-temperature superconductor by observing induced Cu magnetic moments in ferromagnet-superconductor bilayers using x-ray magnetic circular dichroism.
Contribution
It provides the first direct evidence of magnetic coherence in the normal state of a cuprate superconductor through bilayer measurements.
Findings
Cu magnetic moments are induced in YBCO by the ferromagnetic layer.
The Cu moment persists below the Curie temperature for thin YBCO layers.
The Cu moment is suppressed above the superconducting transition in thicker YBCO layers.
Abstract
The existence of coherent magnetic correlations in the normal phase of cuprate high-temperature superconductors has proven difficult to measure directly. Here we report on a study of ferromagnetic-superconductor bilayers of La2/3Ca1/3MnO3/YBa2Cu3O7 (LCMO/YBCO) with varying YBCO layer thicknesses. Using x-ray magnetic circular dichroism, we demonstrate that the ferromagnetic layer induces a Cu magnetic moment in the adjacent high-temperature superconductor. For thin samples, this moment exists at all temperatures below the Curie temperature of the LCMO layer. However, for a YBCO layer thicker than 12 unit cells, the Cu moment is suppressed for temperatures above the superconducting transition, suggesting this to be a direct measurement of magnetic coherence in the normal state of a superconducting oxide.
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