Imaging stray magnetic fields using 3D scanning techniques

Abstract

A new versatile magnetic field scanning system has been developed; based on a Micromagnetics® STJ-020 tunnelling magneto-resistance (TMR) sensor and a 3-axis positioning arm, with a 3D-printed sensor enclosure, precision goniometer and integrated microscopic sight. Calibration of the hardware, quantifying the slack/backlash of the three axes, and the capabilities of the system and its sensors are recounted. The system is capable of; scanning precisely and repeatably at 1 μm/step with a 4 x 2 μm2 sensing area; scanning smooth continuously dynamic magnetic field changes at a sampling frequency up to 1 MHz; producing scans of three-dimensional volumes; and resolving the "eld components along multiple axes. The Scanner Control so7ware (available as open access†) has been developed to be modular, powerful and adaptable, permi9ng large datasets from multiple sensors to be analysed. Studies are made of the domain structure in 3% Grain-Oriented Electrical Steel, Amorphous Alloy materials, Cubexdoubly oriented Si-Fe Alloy and manufactured Planar coils, both statically and when reacting dynamically to externally applied alternating fields. Interpretation of the resulting field maps and comparison of the advantages and disadvantages of the Scanner system over other domain observation methods is given. The ability to scan a three-dimensional volume above the surface of the sample and to derive the Hz and Hx components from only a single axis sensor is developed and demonstrated, both statically and dynamically. The principles are tested against the known geometries of constructed planar coils, the expected fields from which are determined using Finite Element Modelling.The novel developments of the project, and the advantages of the developed Scanner System, culminate in, and are ultimately demonstrated by, the "nal dynamic three-dimensional, component-resolved stray-"eld scan of a volume above the surface of an unprepared sample of coated 3% grain-oriented electrical steel under alternating applied magnetic field