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Amin, O.J. (2022) Electrical Control of Antiferromagnetic CuMnAs. PhD thesis, University of Nottingham.

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Abstract

Antiferromagnetic (AF) materials are expected to become the primary components in next generation magnetic memory devices, due to their ultrafast spin dynamics, robustness against external magnetic fields, and downsize scalability. The most promising candidate material, so far, is tetragonal CuMnAs - a semimetal AF with the required crystal symmetry to host current-induced N´eel spin-orbit torque. This offers a novel way to efficiently manipulate the AF order using electrical pulses.

The work presented in this thesis explores the effect of electrical pulses on the transport properties and AF domain structure in tetragonal CuMnAs thin films, epitaxially grown on GaP(001) and GaAs(001) substrates. It is revealed in the transport measurements that the onset of a large magnetoresistive switching signal, > 1%, occurs above a pulse current density threshold. The signal exhibits a multicomponent exponential relaxation, which is shown to follow N´eel-Arrhenius behaviour. A temperature dependent study of the signal relaxation is compared in three different CuMnAs layers: 20 nm and 45 nm layers grown on GaP(001), and a 60 nm layer grown on GaAs(001). Whilst the relaxation components show a strong dependence on the CuMnAs layer thickness and sample temperature, the extracted material dependent attempt rates all fall within the terahertz range of AF spin dynamics.

Synchrotron based magnetic imaging technique, X-ray magnetic linear dichroism combined with photoemission electron microscopy, is used to directly image current-induced changes to the AF domain structure of devices fabricated from 50 nm layers of CuMnAs grown on GaP(001). At relatively low pulse current densities, 180° domain walls are observed to move between pinning sites in a reversible and repeatable manner, depending on the direction of the pulse. It is also shown that topological AF vortices and antivortices can be stabilized at room temperature in CuMnAs. Vortex-antivortex pairs are generated and moved using electrical pulses. Their coherent movement is reversible and repeatable, in the direction of the pulse.

Item Type:	Thesis (University of Nottingham only) (PhD)
Supervisors:	Wadley, P Edmonds, K
Keywords:	Antiferromagnetic materials, magnetic memory, thin films
Subjects:	Q Science > QC Physics > QC170 Atomic physics. Constitution and properties of matter Q Science > QC Physics > QC501 Electricity and magnetism
Faculties/Schools:	UK Campuses > Faculty of Science > School of Physics and Astronomy
Item ID:	71236
Depositing User:	Amin, Oliver
Date Deposited:	23 Aug 2023 13:06
Last Modified:	23 Aug 2023 13:06
URI:	https://eprints.nottingham.ac.uk/id/eprint/71236

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