Development of a micro-Hall magnetometer and studies of individual Fe-filled carbon nanotubes

Abstract

This work presents Hall magnetometry studies on individual Fe-filled carbon nanotubes (CNT). For this approach high sensitivity micro Hall sensors based on a GaAs/AlGaAs heterostructure with two dimensional electron gas (2DEG) were developed. Electron beam lithography and wet chemical etching were utilized for patterning Hall sensors onto the heterostructure surface. The devices were characterized by means of scanning electron microscopy, atomic force microscopy and transport measurements. Individual Fe-filled CNTs were placed on active part of devices (800 × 800 nm2) with aid of micromanipulator system. Measurements on an individual iron nanowires confirmed devices applicability for measurements of nanoscale magnets. High nucleation fields were found of about 900 mT for a Fe nanowire with diameter of d = 26 nm. The magnetization reversal mechanism was found to be a localized process whereas the angular dependence of nucleation fields is in a good agreement with a curling mode. Through magnetization studies performed on differently functionalized ensembles of CNT by means of Alternating Gradient – and Superconducting Quantum Interference Device (SQUID) magnetometry a strong influence of a remaining ferromagnetic catalyst material on the magnetic properties of CNT was observed. Magnetization studies proved that a post annealing method removes catalyst material completely.