Enhanced magnetic properties in antiferromagnetic-core/ferrimagnetic-shell nanoparticles

Bi-magnetic core/shell nanoparticles are gaining increasing interest due to their foreseen applications. Inverse antiferromagnetic(AFM)/ferrimagnetic(FiM) core/shell nanoparticles are particularly appealing since they may overcome some of the limitations of conventional FiM/AFM systems. However, virtually no simulations exist on this type of morphology. Here we present systematic Metropolis Monte Carlo simulations of the exchange bias properties of such nanoparticles. The coercivity, H C, and loop shift, H ex, present a non-monotonic dependence with the core diameter and the shell thickness, in excellent agreement with the available experimental data. Additionally, we demonstrate novel unconventional behavior in FiM/AFM particles. Namely, while H C and H ex decrease upon increasing FiM thickness for small AFM cores (as expected), they show the opposite trend for large cores. This presents a counterintuitive FiM size dependence for large AFM cores that is attributed to the competition between core and shell contributions, which expands over a wider range of core diameters leading to non-vanishing H ex even for very large cores. Moreover, the results also hint different possible ways to enhance the experimental performance of inverse core/shell nanoparticles for diverse applications

Static and Dynamic Magnetic Properties of La0.8Sr0.2MnO3 Nanoparticles

In this research, nanoparticles of La0.8Sr0.2MnO3 with mean crystallite size of 20 nm have been prepared by sol gel method. The sample has been characterized by X-Ray Diffraction (XRD) using Rietveld refinement, Field Emission Scanning Electron Microscope (FESEM) and Fourier Transform Infrared (FTIR) spectroscopy. The static magnetic properties such as saturation magnetization, effective magnetic moment and ferromagnetic phase fraction of the nanoparticles are determined by different techniques using magnetic hysteresis loop at room temperature. The magnetic dynamic properties of crystalls are studied by measuring AC magnetic susceptibility versus temperature at different frequencies. Néel-Brown, Vogel-Fulcher, critical slowing down models and empirical parameters are used to distinguish between superparamagnetic and superspin glass behaviour in the nanoaprticles. By fitting the experimental data with the models, relaxation time, critical view, magnetic anisotropy energy and effective magnetic anisotropy constant have been estimated. The obtained results support the presence of interacting superparamagnetic behaviour between magnetic nanoparticles of La0.8Sr0.2MnO3. &nbsp