Hopkinson peak and superparamagnetic effects in BaFe$_{12-x}$Ga$_x$O$_{19}$ nanoparticles

TL;DR

This study investigates the thermomagnetic behavior of Ga-substituted barium hexaferrite nanoparticles, revealing Hopkinson peaks and superparamagnetic effects, with particle size analysis confirming superparamagnetic relaxation phenomena.

Contribution

It provides a theoretical and experimental analysis of superparamagnetic effects in Ga-doped barium hexaferrite nanoparticles, including particle size estimation from magnetic data.

Findings

Observation of Hopkinson peaks in thermomagnetic curves.

Confirmation of superparamagnetic relaxation effects.

Calculated particle sizes smaller than TEM measurements.

Abstract

In this article, the thermomagnetic properties of a system of Ga-substituted barium hexaferrite nanoparticles ( ) prepared by ball milling were investigated. The thermomagnetic curves for the samples with x ranging from 0.0 to 1.0 exhibited sharp peaks with high magnetization just below TC (Hopkinson peaks). The height of the peak for our samples was similar or larger than previously observed or calculated values. Theoretical treatment of the experimental data demonstrated that the peaks are due to the effect of superparamagnetic relaxations of the magnetic particle. This effect was confirmed by hysteresis measurements at, and just below the temperature at which the peak occurred. Consequently, the particle diameters were calculated from the experimental data using a theoretical model based on the superparamagnetic behavior of a system of uniaxial, randomly oriented, single domain, non-interacting particles. The calculated diameters of 11 - 26 nm are less than the physical diameters determined from TEM measurements. The factors responsible for the low calculated values are discussed.