Frequency-induced Negative Magnetic Susceptibility in Epoxy/Magnetite Nanocomposites

TL;DR

This paper investigates the unusual diamagnetic behavior of epoxy/magnetite nanocomposites at microwave frequencies, explaining it through a modified Debye relaxation model that accounts for frequency-dependent magnetic susceptibility.

Contribution

It introduces a new theoretical model based on the memory effect to explain frequency-induced negative magnetic susceptibility in nanocomposites.

Findings

Nanocomposites show diamagnetism at microwave frequencies.

The model accurately fits experimental data and predicts transition frequency.

Magnetization cannot synchronize with rapidly changing fields, causing negative susceptibility.

Abstract

The epoxy/magnetite nanocomposites express superparamagnetism under a static or low-frequency electromagnetic field. At the microwave frequency, said the X-band, the nanocomposites reveal an unexpected diamagnetism. To explain the intriguing phenomenon, we revisit the Debye relaxation law with the memory effect. The magnetization vector of the magnetite is unable to synchronize with the rapidly changing magnetic field, and it contributes to diamagnetism, a negative magnetic susceptibility for nanoparticles. The model just developed and the fitting result can not only be used to explain the experimental data in the X-band but also can be used to estimate the transition frequency between paramagnetism and diamagnetism.