Development of nano hall sensors for high resolution scanning hall probe microscopy

Abstract

Scanning Hall Probe Microscopy (SHPM) is a quantitative and non invasive method of local magnetic field measurement for magnetic and uperconducting materials with high spatial and field resolution. Since its demonstration in 1992, it is used widely among the scientific community and has already commercialized. In this thesis, fabrication, characterization and SHPM imaging of different nano-Hall sensors produced from heterostructure semiconductors and Bismuth thin films with effective physical probe sizes ranging between 50nm‐1000nm, in a wide temperature range starting from 4.2K up to 425K is presented. Quartz crystal tuning fork AFM feedback is demonstrated for the first time for SHPM over a large temperature range. Its performance has been analyzed in detail and experiments carried with 1×1μm Hall probes has been successfully shown for a hard disk sample in the temperature range of 4.2K to 425K. Other samples, NdFeB demagnetized magnet, Bi substituted iron garnet and, single crystal BSCCO(2212) High Temperature superconductor were also imaged with this method to show the applicability of the method over a wide range of specimens. By this method, complex production steps proposed in the literature to inspect the non‐conductive samples were avoided. A novel Scanning Hall probe gradiometer has also been developed and a new method to image x, y & z components of the magnetic field on the sample surface has been demonstrated for the first time with 1μm resolution. 3D field distribution of a Hard Disk sample is successfully measured at 77K using this novel approach to prove the concept.