Edson Passamani

TITLE:

Hybrid Ferromagnet-Superconductor Heterostructures: The Superconductor Spin-Valve Effect

ABSTRACT:

In this talk, the Superconducting Spin-Valve (SSV) effect, primarily found in hybrid ferromagnet-superconductor (FM/SC) heterostructures, was explained in terms of changes on the spin state of Cooper pairs, i.e., transitions from a singlet to a triplet state occurring at magnetic inhomogeneous interfaces. Specifically, the SSV effect is measured by a critical temperature change ∆T_C of the SC layer defined by the difference between T_C of the SC layer under two field orientations, i.e., by ∆T_C=T_C^∥ – T_C^⊥, where ∥ and ⊥ are respectively the magnetic field directions in-plane and perpendicular to the film plane. This SSV effect is essential for technological applications of SC in spintronic and sensor devices. For that, we prepared 20 nm thick SC Nb films covered either by FM layers (permalloy-Py or cobalt-Co) or by non-magnetic metals (X) with different spin-orbit couplings (SOC). The studied systems were prepared by DC Magnetron Sputtering in a base pressure of 2 x 10^-8 Torr on Si (100) naturally oxidized substrates forming the following nanohybrids: Co(0-20 nm)/Pt(3 nm)/SC(20 nm)/Si(100), Py(0-20 nm)/Pt(3 nm)/SC(20 nm)/Si(100) and Si/Nb(20 nm)/X-layers, with X = Ti, W, Ta, Pd or Pt and thickness ranging from 3-15 nm. We showed that: (i) the Nb superconducting properties are strongly affected by FM spin structures and/or SOC and (ii) there are large SSV effects in Co/Nb and Pt/Nb nanohybrids. While the explanation for the enhanced SSV effect observed in SC/FM nanohybrids is based on the existence of inhomogeneous magnetic fields from FM layers, the SOC seems to be the main source for the huge ∆T_C value found in SC/X hybrid systems. All these issues will be better discussed during the oral presentation in the conference.

BIO:

Edson C. Passamani is a Full Professor at the Federal University of Espírito Santo (UFES) since February 1997. He holds a Doctorate in Physics from the Brazilian Center for Physics Research (CBPF, 1996), studying “Magnetic Properties of Thin Films and Multilayers using Mössbauer spectroscopy”. He also completed a postdoctoral fellowship at Katholieke Universiteit Leuven in Belgium between 2001 and 2002. His main research interests include the preparation and study of the physical properties of new nanostructured materials, nanomagnetism in thin films and nanoparticles, hybrid systems involving ferromagnets and superconductors. Over the years, he has published around 160 scientific papers, with approximately 2,100 citations and an h-index of 23. He has presented more than 30 invited or oral talks at international and national conferences, delivered over 40 invited lectures at academic institutions in Brazil and abroad, and served as chairperson in more than seven scientific events. He also served as the Head of the Graduate Physics Program at UFES (from 2007 to 2011), was a member of the Scientific Committee of FAPES (the research funding agency at Espírito Santo State, from 2016 to 2021), a member of the Committee of LABNANO at CBPF (from 2009 to 2015) and has been a Brazilian representative on the International Committee of IBAME since 2015. Furthermore, he contributed to the publication and proceedings committees of LACAME in 2010, 2012, and 2022. Since 2002, he has been the leader of the Magnetometry and Mössbauer Effect Laboratory at UFES.