Noise- and force-induced resonances of magnetization and orientation in superparamagnetic systems

We consider higher harmonic generation in an assembly of noninteracting superparamagnetic particles under DC and AC magnetic fields. In a solid system the only quantity that responds is its magnetization. In a magnetic fluid, uniquely, the field-induced particle re-orientation gives birth to oscillations of birefringence and thus the intensity of the transmitted light. Depending on the ratio of the magnetic field strengths (AC-to-DC) and also on the level of noise (temperature), the higher harmonics display a specific resonance-like behavior.