Stimulating neurons and recording their activity are critical for experimental and clinical neuroscience. A variety of techniques exist to enable researchers to interface with neurons. Among them, electrode-based recording and stimulation is a well-proven technology for clinical use. However, micro-electrodes used in in-vivo devices cease to function adequately within a few years due to inflammatory responses in which tissue buildup around the electrode impedes its ability to deliver current or measure activity. In extracellular recording, electrodes pick up the electric field from transmembrane currents which are an indirect measure of intracellular activity. In contrast, neuronally-generated magnetic fields are directly proportional to the intracellular current. Not only does the magnetic field capture new information that is inaccessible with electrode-based recordings, but it also passes through most tissues and insulator materials unattenuated, suggesting that devices creating/measuring the magnetic field can be fully encapsulated in inert materials to mitigate the aforementioned challenges from electrodes. We therefore propose to use magnetic fields to both sense and stimulate neuronal activities. We propose a new magnetic sensor that is sensitive to picoTesla-scale fields, a localized magnetic stimulator with small form-factor, and a seamless integration of both systems for applications in experimental and clinical neuroscience.