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Skyrmion generation and perpendicular magnetic anisotropy modification in Heusler alloy ultrathin films

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thesis
posted on 22.09.2021, 21:54 by Yao Zhang

This thesis explores the magnetic properties of Heusler alloy thin films for spintronics applications. The skyrmion generation under different externalstimulation was focused in MgO/Mn2CoAl/Pd ultrathin films and the anomalous Hall effect of Co2MnGa thin films.

The perpendicularly magnetized MgO/Mn2CoAl/Pd ultrathin films were firstly optimised by changing the thickness of Pd layer so that the effective magnetic anisotropy can be tuned and various magnetic textures can be obtained for different purposes. Based on the understanding of Pd dependence of magnetic properties, The skyrmion generation by applying an in-plane magnetic field was investigated to fine tune the effective magnetic anisotropy. Further the fractal analysis was used to describe the evolution of the magnetic states and categorise the formation of skyrmions.

Then skyrmion generation by ionic liquid gating has been investigated in this trilayer. Both non-volatile and volatile skyrmions can be generated by applying a range of voltage sequences. The potential mechanisms, magneto-ionic and electrostatic charge effects, have been discussed as well.

Finally, the thickness dependence of Co2MnGa thin films was studied. This material can be used as a spin-orbit generator for manipulating skyrmions. A large anomalous Hall angle (AHA) was demonstrated in Co2MnGa thin films (20 - 50 nm) showing a AHA ~11.4% at low temperature and ~9.7% at room temperature, which can be ascribed to the nontrivial topology of the band structure with large intrinsic Berry curvature. However, the anomalous Hall angle decreases significantly with thicknesses below 20 nm, which band structure calculations confirm is due to the reduction of the majority spin contribution to the Berry curvature.

History

Advisor 1

Granville, Simon

Advisor 2

Ruck, Ben

Copyright Date

22/09/2021

Date of Award

22/09/2021

Publisher

Victoria University of Wellington - Te Herenga Waka

Rights License

CC BY-SA 4.0

Degree Discipline

Physics

Degree Grantor

Victoria University of Wellington - Te Herenga Waka

Degree Level

Doctoral

Degree Name

Doctor of Philosophy

ANZSRC Type Of Activity code

4 EXPERIMENTAL RESEARCH

Victoria University of Wellington Item Type

Awarded Doctoral Thesis

Language

en_NZ

Victoria University of Wellington School

School of Chemical and Physical Sciences