Magnetic metasurfaces and superconductor materials for advanced sensors and spintronics

Abstract

Metamaterials with engineered structures have been extensively investigated for their capability to manipulate optical, acoustic, or thermal waves. In particular, magnetic metamaterials with precise geometry, shape, size and arrangement of their elemental blocks may be used to concentrate, focus, or guide magnetic fields. Specifically, their application to concentrate the magnetic field could attract special interest in the field in the novel electric devices such smart phones, watches and even intelligent glasses. Nowadays, the basis to improve these systems is to scale to the nano and micro dimensions of all the involved components. In this way, we aim to developed magnetic flux concentrators in the micro- and even in the nano- scale which are expected to further improve the performance and the applicability to the new technological applications. The study of the enhancement of magnetic field requires a magnetic sensor able to quantify the strength of magnetic field amplification and present high dimensional adaptability to be placed inside the magnetic concentrator. Here we show a detailed study of compatibility and viability for different standard magnetic sensors such as Anisotropic Magnetoresistance, Pole Barber and Planar Hall Effect probes. Specifically, Planar Hall effect (PHE) sensors have been studied widely in a different system and applications due to its interesting properties, such as high sensitivity, thermal stability, and easy fabrication. In this case, we aimed to implement this type of sensor to sense and analyse Magnetic Flux Concentrators (MFC) in the micro- and nano- scale , which requires high magnetic field range of operation to be able to quantify the maximum gain as possible. \\ In this work, we show the potential of using soft-magnetic permalloy (Py) metasurfaces to tailor the physical properties of other magnetic structures at the local scale. As an illustration, the magnetic response of a Cobalt (Co) sensor bar placed at the core of a Py metasurface is investigated as a function of in-plane magnetic fields through the PHE. Our findings reveal that by appropriately selecting metasurface geometrical parameters, the sensitivity of the Co sensor can be dramatically increased by two orders of magnitude. Micromagnetic simulations, coupled with magneto-transport equations and X-ray photoemission electron measurements (XPEEM) with contrast from magnetic circular dichroism (XMCD), accurately capture this effect and provide insights into the underlying physical mechanisms. These findings can potentially enhance the performance and versatility of magnetic functional devices by using specifically designed structural magnetic materials. Moreover, this manuscript also offers a detailed study of magneto-transport measurements in High Temperature superconducting materials to analyses its potential application in spintronics. Spin transport in superconductors offers a compelling platform to merge the dissipationless nature of superconductivity with the functional promise of spin-based electronics. A significant challenge in achieving spin polarisation in conventional superconductors stems from the singlet state of Cooper pairs, which exhibit no net spin. The generation of spin-polarised carriers, quasiparticles, or triplet pairs in superconductors has predominantly been realised through hybrid superconductor/ferromagnet systems through proximity-induced spin polarisation. Historically, cuprate superconductors have been characterised by strong electronic correlations but negligible spin-orbit coupling. Here, we report exceptionally large anisotropic magnetoresistance and a pronounced planar Hall effect arising near the superconducting phase transition in the prototypical high-temperature cuprate superconductor YBCO without using a proximity ferromagnet. These effects, unprecedented in centrosymmetric cuprates, emerge from spin-polarised quasiparticle transport mediated by strong spin-orbit coupling. By systematically tuning magnetic field strength, orientation, temperature, and doping, we show clear evidence of spin-orbit-driven transport phenomena in a material class long thought to lack such interactions. Our findings reveal an unexpected spin-orbit landscape in cuprates and open a route to engineer spintronic functionalities in high-temperature superconductors.

Date of Award	2 Jul 2025
Original language	English
Supervisor	Ana Maria Palau Masoliver (Director)