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Magnetotransport measurements of NiFe thin films and nanostructures

Esien, Kane 2016. Magnetotransport measurements of NiFe thin films and nanostructures. PhD Thesis, Cardiff University.
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Abstract

A custom built thermal evaporator equipped with in situ electrical transport probes and an electromagnet, designed to investigate magnetic thin films and nanostructures, was constructed and calibrated. Magnetoresistance measurements were used to characterise a 20 nm thick film grown in 2 nm steps and measured in situ as a function of film thickness. It was found that the thin film had a smaller than expected anisotropic magnetoresistance (AMR) signal of 0.024%. It was suggested that an oxide formed at each 2nm thick layers during the growth phase altered the conductivity of the film and caused the measured AMR to be anomalously small. Lateral spin valves fabricated from a range of ferromagnetic and normal metal components were investigated. NiFe/Au/NiFe lateral spin valves were the most thoroughly investigated to determine the spin diffusion length in the Au, the spin polarisation of NiFe and the injection efficiency at the NiFe/Au interface. Lateral spin valves fabricated from NiFe/Al/NiFe and utilising tunnelling contacts were also investigated and a pure spin current detected. Other devices, including a non-local lateral spin valve dual spin injection structure, were fabricated and measured. Nanomachining using diamond coated silicon nitride atomic force microscope (AFM) tips was employed to modify nickel iron (NiFe) nanowires. The modifications to nanowires in this way subsequently altered the observed domain wall motion in the wires. AFM nanomachining was found mostly to increase the coercive field of the nanowires owing to the formation of a pinning site for domain walls. Magnetoresistance measurements were used to study the effect of machining nanowires of varying widths and thickness. Theoretical predictions regarding the change in coercive field due to machining were larger than those experimentally measured. Domain wall anisotropic magnetoresistance (DW AMR) was also studied as a function of width for two thicknesses of nanowire (10nm and 20nm). Deviation from existing theoretical models was observed consistently for both wire thicknesses. A dependence of the DW AMR on the proximity to the phase boundary between different domain wall types was observed for each thickness of nanowire studied.

Item Type: Thesis (PhD)
Status: Unpublished
Schools: Physics and Astronomy
Subjects: Q Science > QC Physics
Uncontrolled Keywords: Lateral metallic spin valves, DW AMR, AFM nano-machining, in situ AMR, Thin Film NiFe
Funders: EPSRC, Cardiff University
Date of First Compliant Deposit: 19 April 2017
Last Modified: 19 Oct 2019 03:35
URI: http://orca-mwe.cf.ac.uk/id/eprint/99978

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