000203259 001__ 203259
000203259 005__ 20180501110033.0
000203259 0247_ $$2doi$$a10.5075/epfl-thesis-6316
000203259 02470 $$2urn$$aurn:nbn:ch:bel-epfl-thesis6316-8
000203259 02471 $$2nebis$$a10271654
000203259 037__ $$aTHESIS_LIB 000203259 041__$$aeng
000203259 088__ $$a6316 000203259 245__$$aMagnetic states and spin-wave modes in single ferromagnetic nanotubes
000203259 269__ $$a2014 000203259 260__$$aLausanne$$bEPFL$$c2014
000203259 336__ $$aTheses 000203259 502__$$aProf. V. Savona (président) ; Prof. A. Fontcuberta i Morral (directrice) ; Prof. C.H. Back,  Dr V. Cros,  Dr S. Rusponi (rapporteurs)
000203259 520__ aIn this thesis the electrical properties, magnetic states and spin wave resonances of individual magnetically hollow ferromagnetic nanotubes have been studied. They were prepared from the different materials Nickel (Ni), Permalloy (Py) and Cobalt-Iron-Boron (CoFeB), deposited as shells onto non-magnetic Gallium-Arsenide (GaAs) semiconductor nanowires via Atomic Layer Deposition (ALD), thermal evaporation and magnetron sputtering, respectively. The resulting nanotubes had lengths between 10 to 20 μm, diameters of 150 to 400 nm and tube walls (shells) which were 20 to 40nm thick. Structural analysis of the tubes by Transmission Electron Microscopy revealed a poly(nano)crystalline (Ni, Py) and amorphous (CoFeB) structure. Electrical transport experiments as a function of temperature revealed different transport mechanisms for each of the materials. Electron-phonon scattering dominated the temperature dependence of the resistivity in Ni, while a clear evidence for electron magnon scattering was observed in Py. Electron-electron interaction in granular and amorphous media was identified as the major contribution to the temperature dependence in CoFeB. The Anisotropic Magnetoresistance (AMR) ratios have been determined for all tubes and different temperatures. Ni nanotubes exhibited a large relative AMR effect of 1.4% at room temperature. The AMR measurements provided information about the magnetic configurations as well as the magnetization reversal mechanism. Indications for the formation of vortex segments in Ni tubes were found for the magnetization reversal when the magnetic field was perpendicular to the nanotube axis. In cooperation with the Poggio group in Basel, cantilever magnetometry has been used for the further characterization of the nanotube magnetization. The magnetization curves were compared to the AMR measurements and finite element method (FEM) micromagnetic simulations. The comparison between the experimental results and the simulations suggested that the roughness of Ni tubes gave rise to segmented magnetic switching. An almost perfect axial alignment of the remanent magnetization has been observed in Py and CoFeB nanotubes. The influence of the inhomogeneous internal field in transverse magnetic fields was investigated by simulation. The segment-wise alignment of spins with the field direction is argued to provoke characteristic kinks in the hysteresis curve and measured AMR effect. Magnetothermal spatial mapping experiments using the anomalous Nernst effect (ANE) complemented the magnetotransport experiments in cooperation with the group of Prof. Grundler in Munich. Here, first evidence of end-vortices entering the nanotube before reversal could be found. Electrically detected spin wave resonance experiments have been performed in cooperation with the group of Prof. Grundler on individual nanotubes. The detected voltage, generated by the spin rectification effect, revealed multiple resonances in the GHz frequency. The experimentally observed resonances were compared to calculated ones extracted from dynamic simulations. With this comparison, the signatures could be attributed to azimuthally confined spin-wave modes. The deduced dispersion relation suggested the quantization of exchange dominated spin waves in that resonance frequencies follow roughly a quadratic dependence on the wave vector. 000203259 6531_aferromagnetic nanotubes
000203259 6531_ $$amicromagnetics 000203259 6531_$$amagnetoresistance
000203259 6531_ $$amagnetothermal effects 000203259 6531_$$amagnonics
000203259 6531_ $$amicrowave photovoltage 000203259 6531_$$aNi
000203259 6531_ $$aPy 000203259 6531_$$aCoFeB
000203259 700__ $$0245457$$aRüffer, Daniel$$g201393 000203259 720_2$$0243742$$aFontcuberta i Morral, Anna$$edir.$$g182447 000203259 8564_$$s15251909$$uhttps://infoscience.epfl.ch/record/203259/files/EPFL_TH6316.pdf$$yn/a$$zn/a 000203259 909C0$$0252277$$pLMSC$$xU11832
000203259 909CO $$ooai:infoscience.tind.io:203259$$pDOI$$pthesis$$pthesis-bn2018$$pDOI2$$pSTI
000203259 917Z8 $$x108898 000203259 917Z8$$x108898
000203259 917Z8 $$x108898 000203259 917Z8$$x108898
000203259 917Z8 $$x108898 000203259 918__$$aSTI$$cIMX$$dEDPY
000203259 919__ $$aLMSC 000203259 920__$$a2014-11-14$$b2014 000203259 970__$$a6316/THESES
000203259 973__ $$aEPFL$$sPUBLISHED
000203259 980__ aTHESIS