Electrical control of magnetism in oxide films and devices

Lead Research Organisation: University of Oxford
Department Name: Oxford Physics

Abstract

One of the most promising routes towards a new generation of fast, low-power electronics is the electrical control of magnetism in insulators. This approach exploits the ability to switch the antiferromagnetic state in several classes of oxides by applying a small writing voltage. The spin polarisation can then be transferred to a ferromagnetic material through an interface, and then read in a conventional way, e.g., using a Tunnelling MagnetoResistance junction as in hard-disk reading heads. This scheme could be employed to produce fast and efficient non-volatile memories, with no writing current to produce Joule heating and therefore dissipate energy.

We have recently developed a suite of techniques for simultaneous imaging of antiferromagnetic/ferromagnetic domains and their electrical switching in epitaxial oxide films and devices. We use a combination of synchrotron X-ray diffraction and microscopy, in-house Magnetic Force Microscopy (MFM) and neutron diffraction, which give us access to domains over length scales from 1 cm to < 100 nm. In the past two years, we obtained some very exciting results on thin films and devices of BiFeO3, grown by our collaborators at the University of Madison. In very recent experiments, we directly imagined the process of electrical switching in BiFeO3 and demonstrated the coupling of the BiFeO3 domains with the ferromagnetic domains of a thin metal over-layer. Even more recently, we demonstrated similar effects in epitaxial films of Fe2O3, grown by one of our students in our lab.

This EPSRC-funded DPhil project will give the successful candidate the opportunity to develop this line of research in different directions:
Identify and grow new materials with electrically controllable domains
Experiment with novel methods to switch the magnetic state of the domains, e.g., through the piezoelectric effect.
Build and test prototype devices using electron beam lithography and other clean room processes.
This project is likely to involve a combination of experimental techniques, such as:
Elastic neutron scattering. We will perform experiments on bulk and films samples predominantly at the ISIS facility at Rutherford Appleton Laboratory.
X-ray scattering, including resonant and non-resonant magnetic X-ray diffraction with hard and soft X-rays. We run state-of-the-art laboratory instrumentation in the Clarendon Laboratory, but we perform most of our high-end experiment at the Diamond Light source.
Dielectric and transport measurements. One of our specialities is to perform measurements of ferroelectricity in extremely high magnetic fields (up to 65 T - a record in the UK), using the pulsed-magnetic-field facility in the Clarendon Laboratory, but a complete set of more standard measurements is also available.
Advanced microscopy. We employ spectral microscopy (PEEM) at Diamond, Magnetic Force Microscopy (MFM) and the Magneto-Optical Kerr Effect to image multi-functional domains, which are the fundamental unit of information storage in oxides.
Nanofabrication. We will be using electron beam lithography and other clean-room methods to design and build prototype oxide quantum materials devices.Depending on the candidate's interests, the project may also include a computational element. In collaboration with the Materials Modelling Group in the Department of Materials, we employ Density Functional Theory methods and other computational techniques to model the functional properties of oxides and to predict their behaviour in different architectures.

This project falls within the 'Energy', 'Physical Sciences' and 'Quantum Technology' EPSRC themes.

Publications

10 25 50

Studentship Projects

Project Reference Relationship Related To Start End Student Name
EP/N509711/1 01/10/2016 30/09/2021
1947207 Studentship EP/N509711/1 01/10/2017 30/09/2020 Anuradha Vibhakar
 
Description As a result of the work funded through this award a number of important results have been achieved. Firstly, we have identified the optimum substrate for growing a single domain thin film of (001)h BiFeO3. By performing strain calculations and diffraction measurements, we identified that 99.7% of sub micron domains present in thin films of (001)h BiFeO could be removed. This will further the technological potential of BiFeO3, as only with single domain thin films can we cleanly harnesses intrinsic properties of the functional material, which is necessary to achieve robust and deterministic switching processes. Another important result of this work has involved the determination of the magnetic structure of a new family of materials, the triple A site columnar ordered quadruple perovskites. Thus far we have found that the compounds TmMn3O6 and R2CuMnMn4O12 (R = Y or Dy) adopt collinear or canted ferrimagnetic structures with a large magnetisation (~1uB per transition metal ion). We have also observed that these compounds undergo spin reorientation phase transitions and have understood the mechanism driving the SR transitions in both compounds. In R2CuMnMn4O12 we show that the mechanism driving the transition is novel, and has been previously unobserved.
Exploitation Route Having identified the optimum substrate for growing a single domain film of (001) BiFeO3, our collaborators are currently working on constructing prototype devices that involve the electrical control of the magnetic order in BiFeO3. Our identification of an alternative mechanism for driving spin reorientation transitions in R2CuMnMn4O12, offers the potential for hosting SR transitions in a wider variety of oxide materials. Magnetisation switching, which occurs as a result of a SR transition, is an important ingredient in nanoscale components that are used in spintronic based technology, and hence our findings can increase the possible materials that could be used in SR-based devices and thus advance spintronic technology.
Sectors Electronics

 
Description GMAG Travel Award
Amount $450 (USD)
Organisation American Physical Society 
Sector Learned Society
Country United States
Start 03/2020 
End 03/2020
 
Description IOP Research Student Conference Fund
Amount £300 (GBP)
Organisation Institute of Physics (IOP) 
Sector Learned Society
Country United Kingdom
Start 03/2020 
End 03/2020
 
Description International School of Crystallography, Travel Grant
Amount € 600 (EUR)
Organisation Ettore Majorana Foundation and Centre for Scientific Culture 
Sector Charity/Non Profit
Country Italy
Start 06/2019 
End 06/2019
 
Description St Cross Travel and Research Fund
Amount £500 (GBP)
Organisation University of Oxford 
Sector Academic/University
Country United Kingdom
Start 03/2020 
End 03/2020
 
Description Student Travel and Research Fund
Amount £250 (GBP)
Organisation University of Oxford 
Sector Academic/University
Country United Kingdom
Start 06/2019 
End 06/2019
 
Description National Institute of Materials - Japan 
Organisation National Institute for Materials Sciences
Country Japan 
Sector Academic/University 
PI Contribution We performed the neutron diffraction measurements to determine the magnetic structure of a set of materials. We also did the analysis and interpretation of the neutron diffraction data and results of the magnetic structure refinement.
Collaborator Contribution Our partners synthesised the samples, performed X-ray diffraction to determine the crystal structure of the samples and performed dc magnetometry measurements.
Impact Publication of 3 papers have resulted from this collaboration. Moreover the emergence of a new field of research of the triple A site columnar ordered quadruple perovskites is emerging.
Start Year 2015
 
Description University of Wisconsin, Madison 
Organisation University of Wisconsin-Madison
Country United States 
Sector Academic/University 
PI Contribution In this collaboration I carried out non resonant x ray diffraction measurements on the samples made by our collaborators in the University of Wisconsin. Furthermore I performed strain calculations to determine the optimum substrate to grow a monodomain thin film of (001)h BiFeO3.
Collaborator Contribution Our collaborators grew samples of (001)h BiFeO3 on different substrates. They also performed basic characteristic measurements on the samples.
Impact A paper and two separate experiments have resulted from this collaboration.
Start Year 2012
 
Description Talk to girls interested in STEM (Oxford University) 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach Local
Primary Audience Schools
Results and Impact 30 school girls from schools in Oxford visited the University of Oxford's physics department. I gave a talk about my career and answered questions they had about a career in academia/ physics.
Year(s) Of Engagement Activity 2018