Ferromagnetic Oxide & Unconventional Superconductor Heterostructures for Superconducting Spintronics

Lead Research Organisation: University of Cambridge
Department Name: Materials Science & Metallurgy

Abstract

Superconducting spintronics is the combination of spintronics (the utilisation of electron spin in devices) with superconducting materials. Historically, superconductivity and magnetism were considered incompatible phenomena, but recent developments in nanofabrication have shown that compatibilities and couplings are possible at the interface between superconducting and magnetic materials, and a more complete synergy between the two phenomena is possible through the formation of spin-polarised supercurrents. By depositing ultra-thin films of ferromagnetic and superconducting materials, we can study fundamental physical phenomena occurring at their interfaces, with the aim to control and manipulate spin polarised supercurrents in order to create highly efficient computing devices.

In this PhD, I will create heterostructures using ferromagnetic oxides and high-temperature unconventional superconductors. I will investigate the proximity effects occurring at the interfaces between these materials, and explore the possibility of creating spin polarised supercurrents with unconventional superconductors. A thorough understanding of how to create and manipulate spin polarised supercurrents with unconventional superconductors is critical to developing superconducting spintronic devices which can operate at elevated temperatures.

This project aligns with an EPSRC-JSPS Advanced Materials Grant.

Publications

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Studentship Projects

Project Reference Relationship Related To Start End Student Name
EP/N509620/1 01/10/2016 30/09/2021
1937217 Studentship EP/N509620/1 01/10/2017 31/03/2021 Graham Kimbell
 
Description My studies have focused on the electrical and magnetic properties of epitaxial oxide heterostructures - i.e. nanometer-scale layers of single crystal oxide materials.

I have tried to create oxide superconductor-ferromagnet junctions, but the materials used are highly sensitive to oxygen loss and the junctions cannot easily survive the fabrication process.

I have found that there is an interfacial anti-ferromagnetic coupling between two magnetic oxides, SrRuO3 and La0.7Ca0.3MnO3. These two ferromagnets will prefer to align magnetically anti-parallel to each other if they are touching, but are decoupled when a non-magnetic layer is placed between them. This coupling depends on what substrate these layers are grown on.

In a different project, there has been recent excitement about a 'topological Hall effect' resulting from 'skyrmions' in ultra-thin SrRuO3 films. Skyrmions are magnetic bubbles which may have important technological uses for memory in computers. I have shown that this effect is likely actually an artifact of two separate magnetic regions, rather than an effect from skyrmions (arXiv:2002.06062).

I have also collaborated on projects, growing and characterising yttrium iron garnet films for studies on graphene (arXiv:1905.06866) and ferromagnetic resonance experiments, and I have helped with x-ray and magnetic characterisation of Sr2RuO4 thin films (an unconventional superconductor).
Exploitation Route This work contributes to the understanding of oxide hetero-structures for use in spintronics and superconducting spintronics. The overarching aim of these fields are to provide faster and more efficient computing devices compared to conventional silicon CMOS computers.

Anti-ferromagnetic coupling in SrRuO3/La0.7Ca0.3MnO3 may be used in superconducting spintronic devices, for example unusual magnetic textures can be used to create spin-polarised supercurrents.

Showing that the 'topological Hall effect' in SrRuO3 may actually be an artifact of two magnetic regions is an important part of the debate about skyrmions in this material. This material initially seemed very promising for the study and development of skyrmion-based devices, but this may not in fact be the case.

Being able to grow Sr2RuO4 thin films rather than bulk single crystals will allow other researchers to create heterostructures using this superconductor, allowing more detailed study into the unusual superconducting properties of this material.
Sectors Digital/Communication/Information Technologies (including Software),Electronics

 
Description Poster presentation at 6th CAMatNet meeting 2019 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach Local
Primary Audience Postgraduate students
Results and Impact Presented a poster on oxide superconducting spintronics at the 6th CAMatNet meeting. I was awarded 1st place in the poster competition, and had interesting and insightful discussions about my work with both researchers and professionals from industry - in particular from Zeiss and AIXTRON.
Year(s) Of Engagement Activity 2019
 
Description Poster presentation at Oxide Super Spin conference 2018 in Amalfi, Italy 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Postgraduate students
Results and Impact Poster presentation on spin mixing at oxide superconductor/ferromagnet interfaces given at the 2018 Oxide Super Spin conference in Amalfi, Italy. The discussion session allowed me to discuss results with academics and gave me useful insight into next steps for my research.
Year(s) Of Engagement Activity 2018
 
Description Poster presentation at the 2018 SEFIRA summer school on superconducting electronics, Spain 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Postgraduate students
Results and Impact Presented a poster on oxide superconducting spintronics at the SEFIRA summer school on superconducting electronics in Minorca, Spain, which sparked some interesting discussion with researchers and academics who were involved in more conventional superconducting electronic circuits.
Year(s) Of Engagement Activity 2018
 
Description Presentation in Sapporo, Japan, at the Oxide Super Spin workshop 2018 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Postgraduate students
Results and Impact Gave a 15 minute presentation on "Triplet conversion in epitaxial oxide heterostructures" to an audience of undergraduates, postgraduate students and academics at the 2018 Oxide Super Spin workshop in Saporro, Japan, including a question and answer session afterwards.
Year(s) Of Engagement Activity 2018
 
Description Talk and poster presentation at Oxide Super Spin conference 2019 in Seoul, Korea 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Postgraduate students
Results and Impact Presented a poster on spin mixing at oxide superconductor/ferromagnet interfaces including a discussion session. Gave a 15 minute talk on the anomalous Hall effect in SrRuO3 thin films, plus a question and answer session which sparked some discussion and started 2 collaborations with international groups.
Year(s) Of Engagement Activity 2019