Domain dynamics in strained metal films with perpendicular magnetic anisotropy

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

Abstract

There is currently growing interest in trying to manipulate magnetic properties, including the direction of magnetization in magnetic thin films and nanostructures, using not just magnetic fields or electric currents, but electric fields. The practical reason for this is that electric fields are expected to dissipate less energy in switching the magnetization than either magnetic fields or electric currents, and this could have an important effect on new generations of electronic devices that incorporate nanomagnets, such as magnetic random access memories. Even if used simply in conjunction with existing methods, electric field-induced effects could reduce the power density required in a device and lessen the amount of energy that is lost as heat.

Sufficiently large electric fields can directly affect the tendency of the magnetization in a thin film to point in a particular direction, known as the magnetic anisotropy. The electric field distorts the outer electronic orbitals and couples to the atomic magnetic moments, enabling manipulation of the magnetic anisotropy and hence the magnetization direction. Multiferroic materials, in which magnetism can be controlled by electric fields (and vice versa), are not very useful in themselves because only one of them, bismuth ferrite, is multiferroic at room temperature and the magnetoelectric effect is generally rather small, but in combination with ferromagnetic thin films improved electric control may be achieved by "magnetic exchange" coupling between the two. However, it is a third method of electric field control that will be used in this research, namely, to combine piezoelectric and ferromagnetic materials and utilise the strain coupling between them. A voltage applied to the piezoelectric makes it expand and compress and thereby strains the magnetic film on top, altering its magnetic properties, including its anisotropy. From the point of view of basic research, there has been very little work so far to investigate the effect of strain on the magnetic properties of thin films with an orientation of the magnetization perpendicular to the plane, and in particular on the switching of the magnetization. This study will focus on such perpendicular films, which the Leeds group excels in making, preparing them in both single crystal and alloy form and using magnetic imaging to study the effect of strain on the magnetization dynamics.

Magnetic imaging enables a direct visualisation of the magnetization direction in a thin film, which is generally not uniform but split up into regions, or "domains" where the magnetization direction is different. In perpendicular films the magnetization in the domains may point up or down relative to the film plane. The polarization of light reflected from the film is rotated by an amount that depends on the magnetization direction (the magneto-optic Kerr effect), and this enables the domains to be pictured in an appropriately designed microscope. Such a microscope offers advantages over other forms of magnetic imaging in that it produces large-area images very quickly and requires no special sample preparation. In principle it can also be used to study changes to the domain pattern with a very high (sub-nanosecond) time resolution. These dynamical changes to the magnetization are useful to know when assessing the suitability of the material for electronic devices, which need to operate at high speed. In this project, nanosecond magnetic field pulses will modify the domain pattern, and taking images before and after each pulse will give an insight into the domain dynamics. This will be done as a function of voltage-induced strain from the piezoelectric, providing a route to understanding how electric fields can improve the efficiency of electronic device function.

Planned Impact

Using electric fields to manipulate or switch the magnetization direction in thin magnetic films or nanomagnets via piezoelectric strain could lead to a new generation of spintronic devices that consume very little power. This project will pioneer the study of magnetization dynamics in strained thin magnetic films, leading to knowledge about how to engineer devices that possess both high operating speeds and optimum energy efficiency.

The new spintronic devices that this project could help deliver will feed first into applications in computing, information and communications technologies. Beneficiaries in the first instance will be integrated circuit designers and electronic engineers (and the companies they work for) who will be able to produce better-performing microelectronic components such as digital memories and data processors. The next set of beneficiaries will be those who design computer hard- and software, information and communications systems, who will make use of the new components to produce faster, more efficient ways of storing and processing data, and higher performance consumer electronics. The companies that manufacture such products, as well as the general public, will eventually benefit over a 10-20 year timescale. Low power miniature portable electronic devices are particularly exciting, with potential applications in medical implants and control/sensing in buildings and infrastructure. Consequently, this research could not only stimulate new electronic product development but also lead to improvements in health care and energy efficiency/safety in the built environment. Lastly, the PhD student working on parts of this project will learn industrially relevant technical skills in device fabrication, characterisation and advanced microscopy, which will benefit future employers in academia or industry.

Publications

10 25 50

publication icon
Shepley PM (2018) Domain wall energy and strain in Pt/Co/Ir thin films on piezoelectric transducers. in Journal of physics. Condensed matter : an Institute of Physics journal

 
Description We have understood the effect of piezoelectric strain on thin films with out-of-plane magnetization.
Exploitation Route The findings will be used as a basis for investigations of energy-efficient methods of manipulating nanomagnets.
Sectors Aerospace, Defence and Marine,Digital/Communication/Information Technologies (including Software),Electronics

 
Description The findings have been discussed in talks to high school students as well as in undergraduate lectures.
First Year Of Impact 2016
Sector Education
Impact Types Cultural

 
Description FP7-PEOPLE-2013-ITN
Amount € 657,000 (EUR)
Organisation European Commission 
Sector Public
Country European Union (EU)
Start 09/2013 
End 08/2017
 
Description H2020 FET Open
Amount € 652,000 (EUR)
Organisation European Commission 
Sector Public
Country European Union (EU)
Start 09/2015 
End 08/2018
 
Description NIST-HN 
Organisation National Institute of Standards & Technology (NIST)
Country United States 
Sector Public 
PI Contribution We deposited thin magnetic films.
Collaborator Contribution The films were characterised by Brillouin Light Scattering at NIST.
Impact We have published an article in Phys Rev B.
Start Year 2017
 
Description WALL 
Organisation IBM
Department IBM Research Zurich
Country Switzerland 
Sector Private 
PI Contribution This is an FP7 Marie Curie ITN in which Leeds hosts two PhD students.
Collaborator Contribution The partners between them host a further 11 PhD students and experienced researchers.
Impact The Fellows showcased their work at the European Researchers' Night in Turin in September 2015.
Start Year 2013
 
Description WALL 
Organisation ISI Foundation - Institute for Scientific Interchange
Country Italy 
Sector Charity/Non Profit 
PI Contribution This is an FP7 Marie Curie ITN in which Leeds hosts two PhD students.
Collaborator Contribution The partners between them host a further 11 PhD students and experienced researchers.
Impact The Fellows showcased their work at the European Researchers' Night in Turin in September 2015.
Start Year 2013
 
Description WALL 
Organisation Johannes Gutenberg University of Mainz
Country Germany 
Sector Academic/University 
PI Contribution This is an FP7 Marie Curie ITN in which Leeds hosts two PhD students.
Collaborator Contribution The partners between them host a further 11 PhD students and experienced researchers.
Impact The Fellows showcased their work at the European Researchers' Night in Turin in September 2015.
Start Year 2013
 
Description WALL 
Organisation Sensitec GmbH
Country Germany 
Sector Private 
PI Contribution This is an FP7 Marie Curie ITN in which Leeds hosts two PhD students.
Collaborator Contribution The partners between them host a further 11 PhD students and experienced researchers.
Impact The Fellows showcased their work at the European Researchers' Night in Turin in September 2015.
Start Year 2013
 
Description WALL 
Organisation Singulus Technologies AG
Country Germany 
Sector Private 
PI Contribution This is an FP7 Marie Curie ITN in which Leeds hosts two PhD students.
Collaborator Contribution The partners between them host a further 11 PhD students and experienced researchers.
Impact The Fellows showcased their work at the European Researchers' Night in Turin in September 2015.
Start Year 2013
 
Description WALL 
Organisation University Paris Sud
Country France 
Sector Academic/University 
PI Contribution This is an FP7 Marie Curie ITN in which Leeds hosts two PhD students.
Collaborator Contribution The partners between them host a further 11 PhD students and experienced researchers.
Impact The Fellows showcased their work at the European Researchers' Night in Turin in September 2015.
Start Year 2013
 
Description WALL 
Organisation University of Salamanca
Country Spain 
Sector Academic/University 
PI Contribution This is an FP7 Marie Curie ITN in which Leeds hosts two PhD students.
Collaborator Contribution The partners between them host a further 11 PhD students and experienced researchers.
Impact The Fellows showcased their work at the European Researchers' Night in Turin in September 2015.
Start Year 2013
 
Description Marie Curie School on Spintronics 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Postgraduate students
Results and Impact I gave a seminar on Magnetic Imaging at a summer school for research students.
Year(s) Of Engagement Activity 2014
 
Description Sheffield seminar 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach Regional
Primary Audience Postgraduate students
Results and Impact Research seminar at the University of Sheffield.

Increased awareness of our research activity.
Year(s) Of Engagement Activity 2014