Studies on nanoconfinement effect of NiO-SiO2 spin glass within mesoporous Al2O3 template

Abstract

Nanoconfinement studies in the glass system xNiO-(1-x)SiO2 having x values as 0.2 and 0.4 were carried out by preparing nanocomposites using mesoporous alumina template. These samples were studied using wide and small angle xrd data. BET analysis was conducted to find the surface area and pore size distribution of the virgin and nanocomposite samples. The microstructure and distribution of transition metal ions in the system were delineated using STEM-EDAX mapping. XPS data provide the quantitative analysis of Ni2+/Ni3+ species present in the system. Theoretical modeling using DFT simulations were implemented to understand the nanoconfinement effect which was in corroboration with the experimental findings. The theoretical model was validated using UV-Vis absorption spectrum. The magnetodielectric results were explained considering Catalan’s model having positive magnetoresistance. Nyquist plot studies were employed to visualize the realistic circuit model with contributions from different layers present in the nanocomposites. The temperature dependent resistivity data were explained using small polaron hopping model and the inter-site separation between Ni2+/Ni3+ ions was found to be larger in nano confined system than the corresponding bulk glass. Existence of more conducting species manifest a significant enhancement in percentile change of MD, MR & conductivity values for NC-2 compared to NC-1. Study of ZFC-FC magnetization curves effectively substantiate spin glass characteristics which exhibit freezing temperature at 4.1 K. The existence of spin glass behavior are well interpreted in terms of memory effect and relaxation dynamics study.