Spintronics at Leeds

Lead Research Organisation: University of Leeds
Department Name: Physics and Astronomy

Abstract

With more than 300 papers published on the topic, the Condensed Matter group in Leeds is well known for its work on spintronics - a subject defined by the exploitation of the magnetic moment of electrons instead of charge. Recently the group has appointed two new members of staff bringing us expertise in organic spintronics (Cespedes) and nanomagnetism (Moore). Thus we are one of the first groups to develop high frequency equipment for molecular spintronics in order to research eco-friendly microwave devices. We are also exploring ways of switching magnetisation using the strain developed by an electric field - important for future storage applications. Although we have links among all members of the group, this Platform provides an excellent opportunity to take a strategic look at our activity.

Our broad research strategy will concern the general theme of spintronic metamaterials. Metamaterials are artificial in that the functional properties are not a feature of the natural occurring materials that form the building blocks, but emerge through design and engineering of material combinations. The artificial aspect is often introduced through nanostructuring. An early example arises in optics where sub-wavelength features give rise to new properties such as photonic band-gap crystals. Magnetic metamaterials were at the dawn of spintronics - a multilayer composed of alternating magnetic and non-magnetic metals displays giant magnetoresistance. These properties have been exploited to great advantage in computing and communication. We aim to move from common magnetoresistive devices and spin transport physics into microwave nanodevices that manipulate the interactions between electrons with phonons, magnons and other quasiparticles in hybrid structures.

Building on our recognised strengths of thin film growth, characterisation and magnetotransport we are proposing a programme of engineering materials in combinations that yield fruitful emergent properties - spintronic metamaterials. Our group has a broad background that includes the ability to structure materials at the nanoscale so that cooperative behaviour arises, e.g. combining superconductors with skyrmion spin textures, or injecting pure spin currents from magnets into organics. We will apply this capability to questions in areas identified as strategic such as quantum effects for new technology, beyond CMOS electronics, energy efficient electronics and new tools for healthcare.

We shall pursue this in a way that is very different from a traditional responsive-mode research project. We have identified areas that are scientifically and nationally important and where we can make impact in both academic and technological settings. We will not specify exactly which experiments will be performed, only the type of experiment that is possible. We will use the flexibility of platform funding to develop the independence of researchers beyond that achievable in a normal grant. As an example, there is a controversy at present about the role of heat and magnetic proximity effects in spin currents and their possibilities in non-dissipative, low power consumption electronics. With platform funding we can send a researcher to visit the relevant labs and attend the workshops who would then be in a good position to recommend the best course of action. The researcher would lead those experiments with full support for necessary resources - including and encouraging, if appropriate, the contribution of PhD students and other PDRAs. This general approach can be applied across our whole platform programme to any emerging problems in the field. This is career-enhancing because researchers, at this stage of their research, can usually only gain this level of autonomy if they are independent Research Fellows. This background will fast track them for Research Fellowships or good positions in industry or top level institutions looking for individuals with initiative and vision.

Planned Impact

This platform programme encompasses a broad research programme based around the concept of nanomagnetic/spintronic metamaterials. Spintronics has been one of the most commercially successful nanotechnologies, with the giant and tunnel magnetoresistance effects having delivered the vast, yet cheap, data storage capacity of hard disks upon which the internet/social media revolution has been based. Low power solid state magnetic random access memories that are based on another spintronic effect, the spin transfer torque, are now coming close to market. Future developments will enable nanomagnetic/spintronics information processing, perhaps exploiting unconventional neuromorphic or quantum architectures.
The importance of advanced functional materials and their potential impact is explicitly recognized in their inclusion in the "Great Eight Technologies" identified by BIS, recently augmented by Quantum Technologies. This Platform grant is aimed at directly addressing this challenge, developing new magnetic and spintronic metamaterials that exhibit novel functional properties. A particular area of impact is energy efficient computing, another of the great eight technologies. The central idea is that the materials combinations and nanostructuring forming the metamaterial give rise to emergent properties that are not exhibited by the component parts in isolation: the view encapsulated by Nobel laureate Herbert Kroemer when he coined the famous phrase that "the interface is the device". Our results will have impact in the ITC sector in particular, where spintronics has already enabled the huge amounts of extremely cheap data storage needed to provide social media, such as Facebook, Twitter, and Youtube, free to users. Nevertheless, the reality is that the world's server farms are consuming 30 billion watts of power. Furthermore, only about 10% of this energy is actually used for computation. The remainder is used to keep servers available should an urgent demand be requested, and to run cooling systems to dissipate this enormous amount of waste heat. As long ago as 2008, it was pointed out that the carbon footprint of the internet exceeds that of commercial air travel. As the rates of data production and consumption increase, this is clearly not sustainable. As the data volumes are unlikely to reduce, we need to search for new materials that will permit new devices and architectures to greatly more efficient use of energy, and to scavenge waste heat and turn it back into useful power.
The other principal means of realising impact will be the provision of highly skilled people to the wider world, achieved through the superb training and developmental environment in the Condensed Matter Physics group. Since the academic job market is very limited, it is clear that most of our early stage researchers will, in the fullness of time, have to pursue the next stage of their career in another kind of organisation. Our Platform researchers will develop faster than they otherwise might in a conventional project-based setting, since they will have freedom to propose and pursue their own research goals and thus participate in strategy-setting for the group, undertake secondments to leading international and industrial research partners, and have exceptional opportunities for developing management and leadership abilities through mentoring and helping supervise under- and postgraduate student researchers. Moreover, we have a state-of-the-art laboratory with advanced nanofabrication, synthesis, characterisation, measurement, and simulation capabilities. Acquiring these technical skills is another asset for our researchers as future employees, as demonstrated by our track record of placing graduates the group in leading institutions in academia, national laboratories, and industry.

Publications

10 25 50
 
Description (i) Weak antilocalisation measurements in moderately disordered InAs/GaBs coupled wells allow measurements of the strength of the spin-orbit interaction, and how it is affected by things like temperature and gate voltage, through the spin-orbit length
(ii) that such a structure into which a thin AlSb barrier has been introduced shows an electron-like conduction channel as well as a hybridised one with a much higher effective mass.
(iii) The decrease in the spin diffusion length in pure spin current conduits has been quantitatively explained as due to Kondo scattering from magnetic impurities
(iv) Three terminal devices using pure spin currents have demonstrated Kirrchoff's laws apply.
(v) Tuning domain wall energy with strain, by balancing anisotropy and exchange energies. (vi) The characteristics and commonality of the emergent magnetism effect for future energy and computing metamaterials with minimum ecological impact.
(vii) We find for the first time the effects of pure spin currents on the optical properties of molecular layers, which has potential applications in optoelectronic and low dissipation devices. (viii) Effect of substrate temperature on the magnetic properties of epitaxial sputter-grown Co/Pt, (ix) Discovered the downturn in magnetisation in thin film YIG is due to an extra magnetic layer at the interface between GGG and YIG that orders antiparallel to YIG at low temperatures.
(x) we have gained further understanding of heat transport in nanostructures and how it affects spin transport.
(xi) We have increased the spin polarisation and subsequent spin injection into lateral spin valves - this could be important for furtre devices.
Exploitation Route In the long term these findings will offer technology a means to reduce the energy cost in electronics.
Sectors Digital/Communication/Information Technologies (including Software),Education,Electronics,Energy

 
Description Hitachi Cambridge Labs 
Organisation Hitachi Cambridge Laboratory
Country United Kingdom 
Sector Private 
PI Contribution Joint supervision of Scott Marmion by BJH and Dr David Williams. Worked together on the growth of YIG and the subsequent measurement of the spin Hall MR.
Collaborator Contribution Joint supervision of Scott Marmion by BJH and Dr David Williams.Worked together on the growth of YIG and the subsequent measurement of the spin Hall MR.
Impact Publications.
Start Year 2012
 
Description IBM Zurich 
Organisation IBM
Department IBM Research Zurich
Country Switzerland 
Sector Private 
PI Contribution We collaborate on measurements of domain wall properties and heat transport in nanostructures. We make the samples and they are measured at IBM.
Collaborator Contribution We collaborate on measurements of domain wall properties and heat transport in nanostructures. We make the samples and they are measured at IBM.
Impact There are several papers in preparation and one has been submitted to PRL.
Start Year 2012
 
Description Article in The Conversation: Low-carbon computing is needed to avoid a technological collapse 
Form Of Engagement Activity A magazine, newsletter or online publication
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Public/other audiences
Results and Impact Article to disseminate the impacts that the internet and related technologies have in the environment and how current research contributes to minimise them -while continuing technological progress. Several comments and emails about this activity.
Year(s) Of Engagement Activity 2018
URL https://theconversation.com/low-carbon-computing-is-needed-to-avoid-a-technological-collapse-93381
 
Description Invited Talk at ECMolS 2018 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Third sector organisations
Results and Impact Gave invited presentation at the ECMolS conference 2018 in Peniscola (Spain) about spin physics at C60 interfaces.
Year(s) Of Engagement Activity 2018
URL http://icmol.es/ecmols2018/
 
Description Podcast for "The Conversation": Anthill 23: Bursting the Bitcoin bubble . about Bitcoins, cryptocurrency and physics research contributions to novel technologies with wider reach. 
Form Of Engagement Activity A broadcast e.g. TV/radio/film/podcast (other than news/press)
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Public/other audiences
Results and Impact Podcast to discuss cryptocurrencies, online banking and how new technologies impact our society. My contribution centred around information storage and research in magnetism applied to these technologies.
Year(s) Of Engagement Activity 2018
URL https://theconversation.com/anthill-23-bursting-the-bitcoin-bubble-93337
 
Description Talk at Pint of Science - Leeds 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach Regional
Primary Audience Public/other audiences
Results and Impact Gave a presentation to a general audience about magnetic materials and how our research may be used to reduce some environmental impacts of technological progress - such as mining of rare earths and power consumption.
Year(s) Of Engagement Activity 2017
URL https://pintofscience.co.uk/