<p>This thesis presents transverse magnetoresistance (MR) and Hall resistivity measurements of nickel thin films at temperatures between 280 and 455 K and pressures up to 6 GPa. An experimental system was developed for conducting precise magnetotransport measurements using the current reversal and van der Pauw techniques in combination with a 10 T superconducting magnet. Polycrystalline Ni<sub>0.985</sub>O<sub>0.015</sub> thin film samples were manufactured with preexisting point contacts allowing highly reproducible magnetotransport measurements at pressure in the diamond anvil cell (DAC).</p><p>The magnetic resistivity above the technical saturation of the magnetization was found to decrease linearly to the highest applied fields, 10 T, while the field derivative, 0.010-0.018 µΩ cm T<sup>-1</sup> between 280 and 316 K, increased with temperature and decreased with pressure. The decrease in the magnetoresistance is attributed to spin wave damping of electron-magnon scattering processes at high fields. The magnon mass, 535(14) meV Å<sup>2</sup> at 0 K and 0 GPa, determined from longitudinal magnetic resistivity theory is a slightly increasing function of pressure. Correlation between the zero field resistivity and the extraordinary Hall coefficient (EHC) confirmed side jump scattering as the dominant diffusion mechanism at 0 GPa, however, skew scattering was found to become increasingly important with pressure.</p><p>The effect of oxygen and pressure on the density of states (DOS) at the Fermi level was investigated through total energy band structure calculations using a periodic supercell of 64 atoms to simulate the sample chemistry. The DOS of Ni<sub>0.985</sub>O<sub>0.015</sub> at the Fermi level was found to increase by 27% at 10 GPa relative to 0 GPa. However, when compared to the results for pure Ni, decreases of 60% and 23% occurred for the corresponding calculations at 0 and 10 GPa. The relative differences in the magnetic resistivity are attributed to competing effects between the DOS, average magnetic moment and magnon mass.</p><p>The technique developed for conducting magnetotransport measurements at pressure is applicable to the study of electronic diffusion in ferromagnets as well as geophysical problems such as the geodynamo.</p>
| Identifer | oai:union.ndltd.org:UPSALLA/oai:DiVA.org:uu-4653 |
| Date | January 2004 |
| Creators | Boye, Shawn Alexander |
| Publisher | Uppsala University, Department of Earth Sciences, Uppsala : Acta Universitatis Upsaliensis |
| Source Sets | DiVA Archive at Upsalla University |
| Language | English |
| Detected Language | English |
| Type | Doctoral thesis, comprehensive summary, text |
| Relation | Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, 1104-232X ; 1037 |
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