Recording magnetic fields associated with neuronal activity could have certain advantages over voltage recordings, but current probes to detect such fields are too large for in vivo use. Caruso et al. developed micron-scale 'magnetrodes' and used these in the cat visual cortex to show that the amplitudes of visually evoked event-related fields are on the order of several nanoteslas, thus providing proof of concept for intracortical magnetic field recordings.
Caruso, L. et al. In vivo magnetic recording of neuronal activity. Neuron http://dx.doi.org/10.1016/j.neuron.2017.08.012 (2017)