Magnetism and Verwey transition in magnetite nanoparticles in thin polymer film

TL;DR

This study investigates the magnetic and structural properties of magnetite nanoparticles in polymer films, revealing superparamagnetism, size distribution, and anomalies related to the Verwey transition, using multiple characterization techniques.

Contribution

It provides new insights into the magnetic behavior and structural characteristics of magnetite nanoparticles within polymer matrices, especially around the Verwey transition temperature.

Findings

Nanoparticles are superparamagnetic at room temperature.

Size distribution follows a log-normal law with average diameters 5-7 nm.

Pronounced anomalies observed between 130 K and 200 K related to Verwey transition.

Abstract

Magnetic and structural properties of magnetite nanoparticles stabilized in polyvinyl-alcohol thin films are investigated by using X-ray diffraction (XRD), transmission electron microscopy (TEM), electron paramagnetic resonance (EPR) and static magnetometry techniques. The nanoparticles have well-defined crystallinity, and are superparamagnetic at room temperature. Their size distribution is characterized by the distinct log-normal law (with average diameters near 5-7 nm) and slight maximum near 70-80 nm. The EPR spectra and static magnetization data demonstrated pronounced anomalies in the interval between 130 K (corresponding to Verwey transition) and 200 K. The experimental data obtained can be understood on the basis of the half-metallic electronic structure, complex temperature behavior of the magnetic anisotropy, along with effects of "weak magnetic-electron" sublattice of magnetite.