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Details of Grant 

EPSRC Reference: EP/P019749/1
Title: Antiferromagnetic devices for spintronic memory applications
Principal Investigator: Edmonds, Dr K
Other Investigators:
Rushforth, Dr AW Jungwirth, Professor T Wadley, Dr P
Campion, Dr RP
Researcher Co-Investigators:
Project Partners:
Charles University ETH Zurich Hitachi Ltd
Johannes Gutenberg University of Mainz
Department: Sch of Physics & Astronomy
Organisation: University of Nottingham
Scheme: Standard Research
Starts: 01 April 2017 Ends: 31 March 2020 Value (£): 444,719
EPSRC Research Topic Classifications:
Magnetism/Magnetic Phenomena
EPSRC Industrial Sector Classifications:
Related Grants:
Panel History:
Panel DatePanel NameOutcome
25 Oct 2016 EPSRC Physical Sciences - October 2016 Announced
Summary on Grant Application Form
Almost all modern electronic devices require memory devices for large scale data storage with the ability to write, store and access information. There are strong commercial drives for increased speed of operation, energy efficiency, storage density and robustness of such memories. Most large scale data storage devices, including hard drives, rely on the principle that two different magnetization orientations in a ferromagnet represent the "zeros" and "ones". By applying a magnetic field to a ferromagnet one can reversibly switch the direction of its magnetisation between different stable directions and read out these states / bits from the magnetic fields they produce. This is the basis of ferromagnetic media used from the 19th century to current hard-drives. Today's magnetic memory chips (MRAMs) do not use magnetic fields to manipulate magnetisation with the writing process done by current pulses which can reverse magnetisation directions due to the spin-torque effect. In the conventional version of the effect, switching is achieved by electrically transferring spins from a fixed reference permanent magnet. More recently, it was discovered that the spin torque can be triggered without a reference magnet, by a relativistic effect in which the motion of electrons results in effective internal magnetic fields. Furthermore the magnetisation state is read electrically in such MRAMs. Therefore the sensitivity of ferromagnets to external magnetic fields and the magnetic fields they produce are not utilised. In fact they become problems since data can be can be accidentally wiped by magnetic fields, and can be read by the fields produced making data insecure. Also the fields produced limit how closely data elements can be packed.

Recently we have shown that antiferromagnetic materials can be used to perform all the functions required of a magnetic memory element. Antiferromagnets have the north poles of half of the atomic moments pointing in one direction and the other half in the opposite direction leading to no net magnetisation and no external magnetic field. For antiferromagnets with specific crystal structures we predicted and verified that current pulses produce effective field which can rotate the two types of moments in the same directions. We were able to reverse the moment orientation in antiferromagnets by a current induced torque and to read out the magnetisation state electrically.

Since antiferromagnets do not produce a net magnetic field they do not have all the associated problems discussed above. The dynamics of the magnetisation in antiferromagnets occur on timescales orders of magnitude faster than in ferromagnets, which could lead to much faster and more efficient operations. Finally, the antiferromagnetic state is readily compatible with metal, semiconductor or insulator electronic structures and so their use greatly expands the materials basis for such applications.

This proposal aims to develop a detailed understanding of current induced switching in antiferromagnets though a program of research extensive experimental and theoretical studies and to pave the way to exploitation of this effect in future magnetic memory technologies. We will develop high quality antiferromagnetic materials and smaller and faster devices. We aim to achieve devices in which the antiferromagnetic state has not disordered (single domain behaviour) which will have improved technical parameters and which will be ideal for advancing fundamental understanding. We also aim to demonstrate and study the manipulation of regions of antiferromagnets in which there is a transition between two types of moment orientation (domain walls) using current-induced torques. As well as electrical measurements we will directly study the magnetic order in the antiferromagnetic devices using X-ray imaging techniques and we will carry out extensive theoretical modelling.
Key Findings
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Organisation Website: http://www.nottingham.ac.uk