Exploring Spin Hall effects in spintronic devices

Lead Research Organisation: University of Manchester
Department Name: Computer Science

Abstract

Conventional electronic circuits and devices rely on the charge of electrons (and holes) for their functionality. In the future new, better, and crucially more energy efficient devices might be created using the spin of the electron rather than its charge. The driver for combining spintronics with semiconducting logic is that the continuous miniaturization of semiconducting electronics known as "Moore's law" goes hand in hand with increased power dissipation due to leakage.
This Ph.D. project will focus on developing the understand of fundamental and practical application of a new area of spintronics commonly known as spin-orbitronics or the spin Hall effect. The name arises from the manipulation of spin using spin-orbit coupling. Spin Hall effects were initially considered a mostly academic curiosity until it was recently realised that the spin currents can rival or even exceed those generated by direct injection of spin polarized electrons when made into thin film devices. A prototype three terminal spin Hall device is shown in fig.1.
This project will build on our recent work [1] using the Hall effect to probe the electrical transport properties of magnetic nanodots incorporated into lithographically defined Hall crosses. Adding a third terminal, for example by using an AFM probe or another lithography step, would allow new measurements to be made to determine how the spin-orbit interaction at the interface can be utilised in a device. More generally, three terminal devices open up a range of new possibilities, for example in magneto-electric switches or domain wall devices [2-3] for data storage and/or processing.
In order to understand the maximum potential of these devices new materials need to be explored. Recently 2D magnetic thin films, where the materials are deposited one atomic layer at a time, with perpendicular anisotropy, particularly with the L10 order structure (MnAl, MnGe, FeNi etc.) have gained much interest since they offer advantages as high-density, high efficiency spintronic devices. There is also the potential to include antiferromagnetically ordered materials (IrMn, FeRh) as a functional layer in the device. In order to make progress, the project will initially focus on understanding the optimal magnetic properties (e.g. Co/Pd-NiFe, Co/Ni-NiFe or CoFeB-CoFe hybrid structures) needed to create three terminal devices.
This is an experimental project with very good opportunities to help define the direction of the research. In addition, the project will provide access to, and training in, the state-of-the-art instrumentation and facilities for magnetism and nanodevice research in Manchester. There will also be opportunities to collaborate and network with our existing collaborators in laboratories across Europe.

Publications

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Studentship Projects

Project Reference Relationship Related To Start End Student Name
EP/N509565/1 01/10/2016 30/09/2021
1957212 Studentship EP/N509565/1 01/09/2017 31/03/2021 William James Griggs
 
Description As the size of each bit in traditional magnetic data storage decreases, so too does its inherent robustness to thermal fluctuations. Therefore, the continual pursuit for denser storage media is fundamentally hampered by the requirement for stability. One possible solution is to write information to so-called "exchange springs", which combine the benefits of an easily switchable soft magnetic layer and a thermally stable hard magnetic layer. The work conducted via the awarded funding has elucidated the length scales over which exchange springs are effective; specifically, two thin-film exchange spring structures, one comprising FeRh and FePt and the other comprising NiFe and Co/Pd, have been probed using polarised neutron reflectometry.
Exploitation Route The results of the work funded by this award provide insight towards a realistic approach to next-generation high density data storage devices. The explorative nature of this research allows for multiple channels of subsequent investigation, most critically in the form of work to optimise the structural properties of the exchange springs studied (e.g. work to minimise interfacial roughnesses).
Sectors Digital/Communication/Information Technologies (including Software),Electronics

URL https://aip.scitation.org/doi/10.1063/1.5120622