Magnetic field sensor and method for measuring a magnetic field

A method for measuring a magnetic field using a sensor, the method, comprising:

• radiating a microwave field having a first frequency into at least one measuring location in a crystal, which comprises optically excitable color center defects at least at the at least one measuring location;
• radiating excitation light into the at least one measuring location and detecting resulting fluorescence light from the at least one measuring location;
• applying a deformation force to the crystal which results in local mechanical strain at least in an area of the at least one measuring location, the applying of the deformation force including applying a first deformation force that is selected such that the first frequency corresponds to a resonance frequency of the color center defects under the application of the first deformation force without the magnetic field to be measured and the detected fluorescence light becomes minimal;
• placing the sensor into the magnetic field to be measured in order to bring about a shift in the resonance frequency;
• and
• varying the deformation force applied to the crystal to compensate for the shift in the resonance frequency until a minimum fluorescence signal is again acquired at a second deformation force.