Event Details

Join us as we welcome Dr Freya Johnson from the University of Cambridge to deliver our condensed matter seminar on navigating chiral spin architectures.

Non-collinear antiferromagnets (nc-AFM) hosting triangular spin textures that break time reversal symmetry are recognised as having attractive properties for next-generation memory and computing technologies, with the advantageous properties of ferromagnetic and antiferromagnetic materials combined. The topology of their band structure allows for enhanced intrinsic physical properties, such as the anomalous Hall (AHE), Nernst and magneto-optical Kerr effects, which have been used to understand the underlying magnetic order. In thin films of nc-AFMs, strain plays a crucial role in modifying the intrinsic electronic and magnetic properties. In particular, we have recently shown how large local strain fields, generated by dislocation networks, influence the antiferromagnetic domain state and the intrinsic AHE in nc-AFM by examining films that are either highly lattice mismatched or closely matched to their substrate [1]. These effects are distinct from those caused by global strain fields as measured from X-ray diffraction.

Building upon this work, in this talk I will demonstrate how post-growth annealing in Mn3NiN may be used to trap defects within a thin layer of the film, allowing for coherent growth beyond this layer. By controlling the coherent thickness, we are able to modify the non-collinear antiferromagnetic order. For certain thicknesses, we are able to extend the operational temperature range while simultaneously maximizing the AHE. This result will be critical for application of this material in future spintronic devices.

[1] F. Johnson, F. Rendell-Bhatti, B. D. Esser, A. Hussey, D. W. McComb, J. Zemen, D. Boldrin, L. F. Cohen, The Impact of Local Strain Fields in Noncollinear Antiferromagnetic Films, Adv. Mater., 36, 2401180 (2024); https://doi.org/10.1002/adma.202401180

About the speaker:

Dr Johnson is an 1851 Research Fellow in the Cavendish Laboratory, Department of Physics. Her research involves growth and characterisation of non-collinear antiferromagnetic thin films to develop materials and devices for high speed, energy-efficient computing. Dr Johnson received her PhD from Imperial College London, followed by postdoctoral research at Imperial and at University College London.