  We present a comprehensive method for visualisation and quantification of the
magnetic stray field of magnetic force microscopy (MFM) probes, applied to the
particular case of custom-made multi-layered probes with controllable high/low
magnetic moment states. The probes consist of two decoupled magnetic layers
separated by a non-magnetic interlayer, which results in four stable magnetic
states: +/-ferromagnetic (FM) and +/-antiferromagnetic (A-FM). Direct
visualisation of the stray field surrounding the probe apex using electron
holography convincingly demonstrates a striking difference in the spatial
distribution and strength of the magnetic flux in FM and A-FM states. In situ
MFM studies of reference samples are used to determine the probe switching
fields and spatial resolution. Furthermore, quantitative values of the probe
magnetic moments are obtained by determining their real space tip transfer
function (RSTTF). We also map the local Hall voltage in graphene Hall
nanosensors induced by the probes in different states. The measured transport
properties of nanosensors and RSTTF outcomes are introduced as an input in a
numerical model of Hall devices to verify the probe magnetic moments. The
modelling results fully match the experimental measurements, outlining an
all-inclusive method for the calibration of complex magnetic probes with a
controllable low/high magnetic moment.
