Magnetoresistance and Hall effect measurements of Ni to 6 GPa

Abstract

High field magnetoresistance (MR) and Hall effect measurements have been conducted on modular Ni 0.985O 0.015 thin film samples in the diamond anvil cell between 280 and 316 K at applied magnetic fields up to 6 T and at pressures up to 6 GPa. The magnetic resistivity above the technical saturation of the magnetization is found to be negative, linear and nonsaturating while the magnitude of the field derivative, 0.010 – 0.018 μ Ω cm T - 1 , increases with temperature and decreases with pressure. The decrease in the MR is attributed to spin wave damping of electron magnon scattering processes at high fields and the zero temperature magnon mass, 535(49) meV Å 2 at 1.1 GPa, is found to be a slightly increasing function of pressure. Hall effect measurements indicate that skew scattering becomes increasingly important with pressure. Resistivity measurements at zero applied field, normalized to 1.7 GPa, yield a pressure derivative of - 0.018 ( 1 ) GPa - 1 . The effects of pressure and oxygen on the density of states (DOS) at the Fermi level are investigated using total energy electronic band structure calculations and reveal that the DOS of Ni 0.985O 0.015 increases with pressure but remains significantly less than for Ni at 10 GPa. The average magnetic moment of Ni 0.985O 0.015 decreases from 0.675 μ B at 0 GPa to 0.648 μ B at 10 GPa. The magnon mass and magnetic moment are increasing and decreasing functions of pressure, respectively. These effects dominate over the increase in the DOS at the Fermi level and, correspondingly, the field derivative of the magnetic resistivity is found to decrease relative to zero pressure measurements.