Nonlinearity of dynamic magnetization in a superparamagnetic clustered-particle suspension with regard to particle rotatability under oscillatory field

The magnetization induced by oscillatory magnetic-field in a polydispersive superparamagnetic-suspension shows a nonlinearity which strongly depends on the applied frequency. Referring to the initially-measured complex magnetic-susceptibility in function of field-strength, the highly-nonlinear curve of dynamic magnetization at low frequency tends to be linear at higher frequency. Likewise, the dynamic susceptibility appears to be less field-strength dependent at higher frequency, emphasizing a frequency-dependence of magnetically-induced particle-dynamics. This finding is attributable to the imaginary part of magnetization which saturates at lower field-strength of low-frequency magnetic-field. Hence, Brownian relaxation losses should be constant after the saturation due to a confinement of particle rotations.