Effect of sputtering rate and ion irradiation on the microstructure and magnetic properties of $Ni∕Si3N4$ multilayers

In order to prepare Ni clusters embedded in amorphous $Si3N4$⁠, Ni and $Si3N4$ layers have been alternatively deposited using sputtering techniques. The nominal Ni layer thickness ranged from 2 to 60 Å and the number of layers was varied accordingly so as to keep the total amount of Ni constant. Extended x-ray-absorption fine-structure (EXAFS) spectroscopy has been used to study the Ni clustering as well as the isolated Ni ions in the silicon nitride matrix. For small Ni layer thickness, the Ni layer becomes discontinuous and the average size of Ni clusters can be determined. Aiming to modify the Ni surrounding, samples with the thinnest Ni layers have been irradiated with He and P. The EXAFS results show that the main effect is the removal of the isolated Ni in the $Si3N4$ matrix. The size evolution of the Ni clusters depends on the type of the irradiating ion. A complete magnetic characterization is presented in order to correlate Ni surrounding with the magnetic properties of Ni clusters.