Dynamic radio-frequency transverse susceptibility in magnetic nanoparticle systems

Abstract

A novel resonant method based on a tunnel-diode oscillator (TDO) is used to study the dynamic transverse susceptibility in a Fe nanoparticle system. The magnetic system consists of an aggregate of nanometer-size core (Au)-shell (Fe) structure, synthesized by reverse micelle methods. Static and dynamic magnetization measurements carried out in order to characterize the system reveal a superparamagnetic behavior at high temperature. The field-dependent transverse susceptibility at radio-frequencies (RF), for different temperatures reveals distinct peak structure at characteristics fields (± H K , H C ) which changes with temperature. It is proposed that relaxation processes could explain the influence of the temperature on the field dependence of the transverse susceptibility.) on the MI.

Physics of complex transverse susceptibility of magnetic particulate systems

“…Thus, some of the restrictions in the first theoretical approach of Aharoni et al 8 were overcome [10][11][12][13][14][15] and the increased sensitivity of new experimental TS methods allowed the investigations of magnetic systems with very low concentration of magnetic moments. 3,4,16,17 A very recent development of TS constitutes the complex TS. It was first mentioned by Papusoi 18 in the context of magnetic particulate systems and it spurred a lot of attention as it was presented as a new way to determine the particle volume and anisotropy field distributions of a particulate medium.…”

Probing magnetic anisotropy effects in epitaxialCrO2thin films

“…Recently, we developed a way to conduct transverse susceptibility measurements at radio frequencies with high sensitivity, 17 and used this method to explore the anisotropy in magnetic nanoparticles. 18 Thin-film samples are placed in the core of an inductive coil that forms part of a self-resonant ultrastable tunnel diode oscillator, with a resonant frequency around 5 MHz. The change in resonance frequency is measured as the static field is ramped from negative to positive saturation, and vice versa.…”

Monte Carlo study of the transverse susceptibility in ordered arrays of magnetic nanoparticles

“…For RTS measurements the characteristic measuring time is 19,20 τ m = 2 · 10 −5 s, and one obtains τ f = 100 for T = 0.94T b and τ f = 10 for T = 1.16T b . Therefore, the static approximation is reasonably justified for temperatures up to ∼ 20% above the blocking.…”

“…The ac field is weak (∼ 10 Oe) and its frequency lies in the rf regime (f ∼ 10 6 Hz). 10,19,20 . These experimental conditions allow the following approximations to be adopted in the calculation of the RTS.…”

“…Despite of these difficulties,the RTS technique was further developed and applied successfully to the analysis of the dynamical magnetic behavior of magnetic NP assemblies. 19,20,21,22 These studies have demonstrated the capability of the technique to probe efficiently the transition of the NPs from the blocked to the superparamagnetic regime by analyzing the field and temperature dependent RTS curves. Analysis of the peak structure, provided evidence of the presence of interparticle dipolar interactions in dense assemblies of γ -Fe 2 O 3 20 and Co 21,22 NPs.…”