Positive and negative magnetocapacitance in magnetic nanoparticle systems

TL;DR

This study investigates the dielectric and magnetocapacitive properties of magnetic nanoparticles MnFe₂O₄ and γ-Fe₂O₃, revealing significant field-dependent effects linked to magnetic moments and extrinsic mechanisms.

Contribution

It demonstrates the presence of magnetocapacitance in magnetic nanoparticles and relates dielectric changes to magnetic properties, highlighting extrinsic effects as the origin.

Findings

Magnetocapacitance as large as 0.4% at 10kOe

Dielectric anomalies coincide with magnetic blocking temperature

Magnetic field effect proportional to square of magnetization

Abstract

The dielectric properties of MnFe$_2$O$_4$ and $\gamma$-Fe$_2$O$_3$ magnetic nanoparticles embedded in insulating matrices were investigated. The samples showed frequency dependent dielectric anomalies coincident with the magnetic blocking temperature and significant magnetocapacitance above this blocking temperature, as large as 0.4% at H = 10kOe. For both samples the magnetic field induced change in dielectric constant was proportional to the square of the sample magnetization. These measurements suggest that the dielectric properties of magnetic nanoparticles are closely related to the disposition of magnetic moments in the system. As neither bulk gamma-Fe2O3 nor MnFe2O3 are magnetoelectric materials, this magnetodielectric coupling is believed to arise from extrinsic effects which are discussed in light of recent work relating magnetoresistive and magnetocapacitive behavior.