Dynamic radio-frequency transverse susceptibility in magnetic nanoparticlesystems

A novel resonant method based on a tunnel-diode oscillator is used to study the dynamic transverse susceptibility in a Fe nanoparticle system. The mag netic system consists of an aggregate of nanometer-size core (Au)-shell (Fe ) structure, synthesized by reverse micelle methods. Static and dynamic mag netization measurements carried out in order to characterize the system rev eal a superparamagnetic behavior at high temperature. The field-dependent t ransverse susceptibility at radio-frequencies for different temperatures re veals distinct peak structure at characteristics fields (+/- H-K,H-C) which changes with temperature. It is proposed that relaxation processes could e xplain the influence of the temperature on the field dependence of the tran sverse susceptibility. (C) 2000 American Institute of Physics. [S0021-8979( 00)31708-X].