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Strain control of advanced magnetic systems for spintronic applications



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Welbourne, Alexander 


Application of strain to magnetic systems offers the promise of a novel, low energy cost method of manipulating magnetic behaviour. However, many possibilities remain unexplored when it comes to its application to more advanced magnetic systems. Much of the experimental work in this area, focused on spintronic applications, has been targeted at thin single layer films, exploring interfacial effects between ferroelectric and magnetostrictive components. Spintronics, however, utilises a range of advanced magnetic systems to allow for maximum control of properties. This work examines new avenues towards the control of advanced spintronic systems by exploiting magnetostrictive phenomena. From the rich behaviour of synthetic antiferromagnetic films grown by sputtering, to laterally-patterned nanostructures, directly-written using focused beam induced deposition techniques (FBID). In this work, commercial PZT actuators provide strain control to samples via application of voltage. The reproducible, linear, voltage-strain behaviour allows for focus to be on the magnetic, rather than ferroelectric, behaviour. Kapton has been used as a deposition substrate as its flexibility allows for maximal strain transfer as well as offering promise in the field of flexible spintronics. The growth of high quality magnetic systems, in most cases comparable to on Silicon, has been achieved.

Synthetic antiferromagnets: RKKY coupled bilayer samples with in-plane magnetisation have been sputtered. They exhibit a range of switching behaviour dependent on the ratio of coupling to anisotropy: from spin flip to spin flop to single transition regimes. By tuning the anisotropy via strain, this work demonstrates that it is possible to reversibly change a single sample between regimes. Additionally, rotation of the easy axis under strain has been studied, where the ability to revert the switching order of the layers is demonstrated.

FBID nano-structures: FEBID (electron beam) has been used to grow magnetic nanostructures onto actuators using the well understood cobalt precursor gas. Whilst changes in magnetic behaviour are demonstrated, further work looks at deposition of highly magnetostrictive FeGa alloys using FIBID (ion beam) based on a Ga+ source.

This work demonstrates the potential for strain control of advanced magnetic systems as a rewarding avenue of study for spintronic devices.





Fernández-Pacheco, Amalio


Spintronics, Strain, Multiferroics, FEBID, FIBID, Thin film magnetism


Doctor of Philosophy (PhD)

Awarding Institution

University of Cambridge
Engineering and Physical Sciences Research Council (EP/M008517/1)