Magnetic nanoparticles are characterized by a magnetic moment that can be manipulated in an external alternating magnetic field. The typical superparamagnetic behavior leads to a dynamic and especially nonlinear response. This nonlinear response behavior can be represented as an amplitude and phase spectrum with a whole chain of higher harmonics (oscillations). The exact shape of this spectrum is unique to the particle under investigation and can provide information about its properties. The measurement for this takes only a few milliseconds and works everywhere. Unlike static measurement methods, which measure the magnetic moment of the particles directly, for example with magnetometers, this method does not require any complex nitrogen or helium cooling. Therefore, the measurement apparatus can also be easily adapted to the task at hand. Due to the spectral nature of the signal, background-free marker signal can be measured very sensitively, independent of ambient effects.