Abstract: A magnetic sensor having a layer of nonmagnetic insulator including at least one layer of ferromagnetic particles. This combination of layers is sandwiched between two ferromagnetic electrodes. Electrons are transported by the tunneling effect between each electrode and the ferromagnetic particles. The tunneling resistance depends on the orientation of the magnetization of the electrodes and therefore varies in the presence of the magnetic field. The multichannel and multistage nature of the tunneling conduction eliminates the problems of short-circuiting by porosity, thus leading to less difficult fabrication and improved robustness in terms of breakdown. The possible thermal fluctuations of the magnetic moments of the aggregates can be suppressed by the choice of a magnetic material for the part of the insulating layer which contains the aggregates.