ARRAYS OF MAGNETICNANOSTRUCTURES:A DYNAMICAL AND STRUCTURALSTUDY BY MEANS OF X-RAYEXPERIMENTS

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Abstract

The work in this PhD thesis covers two strands of x-ray experiments- firstly, the characterisationof large arrays of dense structures by means of x-ray scattering and secondly,the investigation of hybrid anisotropy square structures with x-ray microscopy.The ability to accurately characterise large arrays of nanoscale magnetic structures isa key requirement for both scientific understanding and technological advance suchas bit patterned recording media (BPM). In this work small angle x-ray scattering(SAXS) was investigated as a characterisation technique for large arrays of patternedstructures. Dense arrays of magnetic nanostructures were prepared on x-ray transparentmembranes and measured. The SAXS data was then modelled to obtain structureparameters such as the mean structure diameter, the diameter distribution and themean position variance with statistical significance. Arrays (500 x 500 μm2) of nominallyuniform nanostructures with centre-to-centre distances between 250 nm-50 nmwere structurally characterised and compared to structure diameters obtained by opticalscanning electron microscopy measurements. The mean structure diameter wasfound to be between 39 nm-15nm and agree within the errors with the diameter obtainedfrom SEM measurements. This work provides accurate data on the distribution(variance) of nanostructure sizes which is key for modelling these arrays for applicationin BPM.In the second part of the work, the static and dynamic properties of patterned hybridanisotropy square structures ([Co/Pd]-Py) were investigated by using time-resolvedscanning transmission X-ray microscopy (STXM). In these patterned structures themagnetisation in the layers change both in magnitude and direction and gives rise tointeresting new domain configurations. The reciprocal interaction between magneticvortices in the Py layer and locally circular stripe domains in the Co/Pd was investigatedand a mutual domain imprint between the layer was observed. In dynamicexcitation experiments the precession of the vortex core is studied and showed goodagreement with micromagnetic simulations made by Hrkac and Bryan. As demonstratedpatterned hybrid anisotropy square structures have promising magnetic propertieswith potential applications in data storage (vortex switching) or spintronics (vortexoscillators).

Layman's Abstract

The work in this PhD thesis covers two strands of x-ray experiments- firstly, the characterisationof large arrays of dense structures by means of x-ray scattering and secondly,the investigation of hybrid anisotropy square structures with x-ray microscopy.The ability to accurately characterise large arrays of nanoscale magnetic structures isa key requirement for both scientific understanding and technological advance suchas bit patterned recording media (BPM). In this work small angle x-ray scattering(SAXS) was investigated as a characterisation technique for large arrays of patternedstructures. Dense arrays of magnetic nanostructures were prepared on x-ray transparentmembranes and measured. The SAXS data was then modelled to obtain structureparameters such as the mean structure diameter, the diameter distribution and themean position variance with statistical significance. Arrays (500 x 500 μm2) of nominallyuniform nanostructures with centre-to-centre distances between 250 nm-50 nmwere structurally characterised and compared to structure diameters obtained by opticalscanning electron microscopy measurements. The mean structure diameter wasfound to be between 39 nm-15nm and agree within the errors with the diameter obtainedfrom SEM measurements. This work provides accurate data on the distribution(variance) of nanostructure sizes which is key for modelling these arrays for applicationin BPM.In the second part of the work, the static and dynamic properties of patterned hybridanisotropy square structures ([Co/Pd]-Py) were investigated by using time-resolvedscanning transmission X-ray microscopy (STXM). In these patterned structures themagnetisation in the layers change both in magnitude and direction and gives rise tointeresting new domain configurations. The reciprocal interaction between magneticvortices in the Py layer and locally circular stripe domains in the Co/Pd was investigatedand a mutual domain imprint between the layer was observed. In dynamicexcitation experiments the precession of the vortex core is studied and showed goodagreement with micromagnetic simulations made by Hrkac and Bryan. As demonstratedpatterned hybrid anisotropy square structures have promising magnetic propertieswith potential applications in data storage (vortex switching) or spintronics (vortexoscillators).

Keyword(s)

BPM; Bit Patterned Media; SAXS; STXM; magnetic vortex oscillator; small angle scattering

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