Magnetic properties and short-range structure analysis of granular cobalt silicon nitride multilayers

The magnetic properties and local order of cobalt/silicon nitride metal-insulator multilayered system have been studied. Magnetization characterization reveals an evolution of the magnetic features by varying the metal layer thickness. Results show that multilayers with larger metal thickness (t) present a pure ferromagnetic character, whereas samples with t < 2 nm exhibit a granular superparamagnetic behavior, as it corresponds to discontinuous metal-insulator materials. An important decrease in the magnetization values for the clustered samples has also been observed. X-ray absorption near edge spectroscopy (XANES) and extended x-ray absorption fine structure (EXAFS) at the Co K-edge have been used to determine the local order and electronic configuration around cobalt. Results reveal the formation of an intermediate CoN phase likely located at the Co/Si3N4 interface. Further insight in the electronic structure of cobalt atoms has been investigated through ab-initio XANES calculations based on Green function’s multiple scattering formalism. Local-projected density of states (l-DOS) obtained by simultaneous computations has unveiled the effects of the nitrogen coordination in the electronic structure of the metal atom around the Fermi energy.This work was supported by Spanish MICINN Contract No. MAT2009-08786.Peer reviewe