Magnetism and Verwey transition in magnetite nanoparticles in thin polymer film

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 the magnetite.

► Structural properties of magnetite nanoparticles in polyvinyl-alcohol thin films are investigated.
► Magnetic properties were studied by static magnetometry techniques, especially near the Verwey transition.
► The data obtained are discussed on the basis of complex temperature behavior of magnetic anisotropy.
► The EPR spectra and static magnetization data demonstrated clear anomalies in the interval 130–200 K.