Magnetotransport Measurements of Ni Thin Films

In this report, we offer transverse magnetoresistance (MR) and Hall resistivity measurements of nickel thin films at temperatures between 280 and 455 K and pressures up to 6 GPa. A new system was developed for carrying out precise magnetotransport measurements making use of the current reversal and van der Pauw methods in combination with a 10 T superconducting magnet. Polycrystalline Ni0.985O0.015 thin film samples were produced with pre-existing point contacts permitting hugely reproducible magnetotransport measurements at pressure in the diamond anvil cell (DAC).The magnetic resistivity over the technical saturation of the magnetization was observed to reduce linearly to the highest applied fields, 10 T, while the field derivative, 0.010-0.018 µ? cm T-1 between 280 and 316 K, improved with temperature and decreased with pressure. The reduction in the magnetoresistance is due to spin wave damping of electron-magnon scattering processes at high fields. The magnon mass, 535(14) meV Å2 at 0 K and 0 GPa, determined from longitudinal magnetic resistivity theory is a somewhat 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, nevertheless, skew scattering was discovered to become increasingly significant with pressure.The effect of oxygen and pressure on the density of states (DOS) at the Fermi level was researched by means of total energy band structure calculations utilizing a periodic supercell of 64 atoms to simulate the sample chemistry. The DOS of Ni0.985O0.015 at the Fermi level was discovered to grow by 27% at 10 GPa relative to 0 GPa. Nevertheless, in comparison with the outcomes for pure Ni, decreases of 60% and 23% occurred for the corresponding calculations at 0 and 10 GPa. The relative variations in the magnetic resistivity are caused by competing effects between the DOS, average magnetic moment and magnon mass.The strategy created for performing magnetotransport measurements at pressure is relevant to the research of electronic diffusion in ferromagnets as well as geophysical problems like the geodynamo.

Contents

1. Introduction
2. Experimental techniques
2.1. Introduction
2.2 Van der Pauw technique
2.3. Experimental system
2.3.1. Instrumentation
2.3.2. Zero pressure cell
2.3.3. Diamond anvil cell
2.4. Samples
3. High field magnetoresistance measurements
3.1. Ni0.985O0.015 thin films
3.1.1. High field magnetoresistance
3.1.2. The Hall effect
3.1.3. Band structure calculations
3.1.4. Pressure effects
3.1.5. Geophysical implications
4. Concluding remark
Summary in Swedish
Acknowledgements……..

Source: Uppsala University Library

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