Optimization of Hall Magnetometry and Single Magnetic Nanoparticle Measurements

This dissertation presents work on improving the sensitivity of Hall magnetometry for single magnetic nanoparticle measurement by miniaturizing the devices down to submicron range. Limiting factors for Hall device performance, including noise and mesoscopic effects, will be explored. The first systematic low-frequency Hall noise measurements on submicron GaAs/AlGaAs 2DEG devices have been carried out at temperatures between 1.5K and 75K in order to understand the microscopic origin of 1/f noise in the Hall signals and to improve device performance. A surprisingly large gating effect was found, which suppresses the 1/f noise level up to several orders of magnitude with application of a modest gate voltage. Detailed temperature and gate voltage dependences of the noise spectra have been analyzed, and the data suggest that the noise originates predominantly from impurity switching processes and their dynamics in the selectively doped AlGaAs layer. This remote origin of the noise is further supported by the fact that the noise is almost independent of electron temperature but varies strongly with lattice temperature. A crossover from thermal activation to quantum tunneling was observed at T