X-ray imaging and spectroscopy of single antiferromagnetic NiO nanoparticles

Abstract

NiO nanoparticles (NP) exhibit relevant physical features when compared to the bulk materials, such as charge-transfer effects and interesting antiferromagnetic (AF) spin structure. Chemical and magnetic studies are often limited to ensembles of NiO NP which are limited to averaging their individual electronic, and magnetic properties with respect to their individual characteristics. In this work, we have analyzed with single-particle sensitivity the chemical, and magnetic properties of three samples of NiO nanoparticles in a size range of 40-60 nm, synthesized by wet chemistry routes, by means of synchrotron-based X-ray Photoemission Electron Microscopy (X-PEEM) combined with X-ray Magnetic Linear Dichroism (XMLD) around the Ni L3,2 edges. The analysis of the local Xray absorption spectra indicates a strong dependence of the oxidation state of the individual NP with the oxidation protocol of each sample. Furthermore, first evaluation of the XMLD signal with respect to the linear polarization angle, a signature of AF order, indicates different AF spin easy axis orientations between individual NiO NP