Quantitative and Traceable Measurement Techniques for Magnetic Microstructures

Abstract

For the quantitative characterization of scientific and industrial relevant magnetic microstructures traceably calibrated measurement techniques are required. Here, two magnetic stray field detection approaches, namely scanning Hall probe microscopy (SHPM) and magneto-optical indicator film (MOIF) technique, are presented. Hall sensors based on gold and graphene with active areas down to 50 nm x 50 nm were fabricated utilizing electron beam lithography. After the characterization, gold Hall sensors on cantilever tips were integrated into an atomic force microscopy based scanning system. This allowed the traceable measurement of the stray field distribution of a magnetic scale under ambient conditions. To complete the calibration process, a systematic uncertainty analysis for the Hall sensor characterization as well as for the SHPM was performed. The results were verified by comparison to the output from two simulation approaches. Moreover, a calibration procedure for fast magnetic sample measurements based on the magneto-optical Faraday effect is introduced and demonstrated on the example of a commercial MOIF device. First, a macroscopic calibration is executed which relates the intensity measured by the device to the homogeneous, magnetic flux density applied perpendicular to the sensor surface by an electromagnet. Properties of the electromagnet and the behavior of the MOIF device itself enter into the detailed uncertainty budget. This pixel-wise calibration incorporates spatially varying MOIF properties and a inhomogeneous illumination as well as the influence of magnetic anisotropies of the MOIF material which were ascertained via ferromagnetic resonance measurements. Second, the microscopic calibration has the aim of simulating the device response to stray fields of microscale magnetic samples with spatially fast varying magnetic fields. For the here utilized MOIF, a significant effect of in-plane stray field components and a neglectable influence of the MOIF thickness was observed. The validity of not only implemented but also traceably calibrated SHPM and MOIF techniques was proven by a cross-comparison of results from the characterization of a magnetic scale under consideration of the uncertainty budgets. The results of this thesis enable the metrological traceable characterization of magnetic stray fields on scales of a few micrometer and in a field range from 2 mT to 1 T.