A sensor for measuring the magnetic flux of a sample material includes a first pick-up coil for generating a pick-up signal and a second pick-up coil for generating another pick-up signal. The first and second pick-up coils are arranged such that they have a substantially equal sensitivity with respect to a background field and a substantially equal sensitivity with respect to deviations from a central position within the coils. The coils have a different sensitivity with respect to a field generated by the sample. The sensor can be used to measure the magnetic response of magnetic material in a varying background field, e.g. for full hysteresis measurement equipment using pulsed magnetic fields. The invention also has applications in a meter for magnetic moment and in measuring induced currents in metallic samples, where it is necessary to make a measurement in the presence of an unwanted background field.