Magnetism of cobalt during oxidative ageing: A theory supported experimental investigation

Highlights: • Ageing study of chemically derived Co microstructures. • Atomistic simulation of temperature-dependent magnetization in Co/CoO core–shell. • The density of states and band structure for fcc and hcp cobalt. The present work investigates the crucial issue of oxidative corrosion of cobalt and its influence on the magnetic properties, with the support of suitable models. The synthesis of cobalt microstructures with controllable morphologies was accomplished by a facile wet-chemical reduction route without the aid of a magnetic field. The magnetic dipolar interactions drive cobalt microparticles to self-assemble and, forming one-dimensional cobalt microchains. The density of states and the band structure of cobalt were determined using ab-initio simulations in both hcp and fcc phases. Transmission electron microscopy images of the aged cobalt particles show core–shell nature, possessing a cobalt core and a cobalt oxide shell. The impact of ageing and the exchange bias phenomenon of cobalt microstructures are profoundly investigated in the manuscript with the help of magnetic and XPS measurements. These results were supplemented by atomistic simulation, which was used to model the temperature-dependence of magnetic properties in aged cobalt particles.