Abnormal Hall Effect In Nickel And Gallium - Manganese

Highlighted by the2007Nobel Physics Prize awarding to Albert Fert and Peter Grunberger, Spintronics has become the forefront of physics research. As an emerging cross-discipline including condensed matter physics, nano-material and electronic engineering, Spintronics has brought profound issues in fundamental physics research and extensive application prospect in future nano-electronics. Among these physics issues, microscopic mechanism underlying spin related transport property has long been a hotspot. During my Ph.D study, I have focused on two typical spin related Hall effect:anomalous Hall effect (AHE) in magnetic3d metals and spin Hall effect (SHE) in strong spin-orbit coupling system. My thesis mainly contains the following works: identifying the intrinsic and extrinsic contribution of AHE in Ni, strictly investigating the AHE scaling of GaMnAs in dirty limit, conducting nanofabrication of Au device for SHE study.1. AHE has long been a puzzled issue in condensed matter physics due to its diverse experimental manifestation, delicate intrinsic nature determined by electronic band structure, and entangled intrinsic and extrinsic contributions. By exploring AHE in nanoscale thick Ni film, we succeed to identify the prevailing intrinsic contribution from5to330K in terms of Hall conductivity. The obtained intrinsic Hall conductivity appears strongly temperature dependent, which explains the known significant divergence between first principle calculation and experimental result. We also obtained considerable inelastic skew scattering contribution at low temperature while the side jump effect is negligible. Our strategy to identify underlying mechanisms and their temperature dependence provides a new experimental approach to gain better insight of spin related Hall effect and pave the way to better artificial design of spintronic device at room temperature.2. Through gradually building up the optimum anneal in (Ga,Mn)As. We found an ideal anneal window, where annealing only changes sample conductivity but not magnetization M, to test the power law scaling of anomalous Hall effect in the dirty limit regime. Only in such anneal window we can ensure the unchanged intrinsic nature and spin polarization, which is crucial to strictly test the scaling law. The result unambiguously indicated that anomalous Hall conductivity (AHC) is independent on longitudinal conductivity. Thus AHE in GaMnAs behaves more like a magnetic metal (Fe, Co) in moderate conductivity regime, not like magnetic oxide in low conductivity regime although conductivity of GaMnAs lies in the latter regime. We further found strong correlation between AHC and M, which might explain the appearance of non-integer scaling exponent. Finally, we determined the prevailing intrinsic contribution in Ga0.93Mn0.07As and the obtained intrinsic AHC value is in good agreement with theoretical estimation.3. A giant SHE was recently observed in Au-based nano-electric device at room temperature, which might be a crucial progress for the application of SHE in spin-electronics. SHE and AHE arise from the same microscopic mechanisms and manifest themselves in non-magnetic and magnetic materials respectively. Therefore, basing on the approach adapted in AHE study, we will firstly identify the physical origin of the giant SHE and then try to manipulate such effect by tuning device thickness and adding magnetic impurity. For the first step, I have conducted the nano-fabrication of nano-scale device on Au/Si system with e-beam lithography.