The system for measuring a magnetic resonance signal within a sample (4) placed in a static exterior magnetic field (H), comprises an excitation device (1 to 3, 6 to 10) for applying radio frequency pulses of strong intensity at a predetermined emission frequency fe in a measurement zone containing the sample (4). The excitation device comprises an excitation coil (3) aligned with the predetermined emission frequency fe and disposed in the vicinity of the sample (4) in such a way as to emit an electromagnetic field essentially perpendicular to the static exterior magnetic field (H). The system furthermore comprises at least one supraconducting-magnetoresistive hybrid sensor (5) comprising a supraconducting loop furnished with a constriction able to significantly increase the density of the current and at least one magnetoresistive sensor placed in immediate proximity to the constriction, while being separated from the latter by an insulating deposition.