Accessible and thorough magnetic field mapping of TEMs using a commercial Hall-sensor and TEM automation for in situ magnetic experiments

For imaging and quantitative in situ experiments of magnetic materials in the transmission electron microscope (TEM), knowing the external magnetic field over the sample position and the parameters affecting it is crucial. Calibrating this thoroughly also requires an efficient method for sampling a large set of parameters. This work presents accessible solutions to both these problems, using a commercial Hall-sensor soldered onto a custom printed circuit board then inserted into a TEM biasing holder. This is enhanced by TEM automation using open-source Python scripting, enabling thorough and effective experimental measurements. The magnetic field in the sample position was measured over a range of positions, tilts and lens excitations for three different TEMs: The JEOL JEM-2100F. JEOL JEM 2100,and JEOL JEM-ARM200F. In objective lens-off mode these have remnant fields of up to respectively 19.19 mT, 15.24 mT and 8.95 mT, all oriented downwards in the column. The magnetic fields had a strong decay in x- and y-positions of up to 13.1%. The objective lens gave a highly linear response to lens excitation up to 27.5% of max excitation. For the 2100F and 2100, fully exciting the objective lens caused a significant change in remnant field of above 4 mT which was counteracted with lens relaxation. The image aberration corrector lenses in the ARM200F caused changes of 0.2 mT. This magnetic field mapping enables quantitative in situ experiments with magnetic fields up to 2 T.