Magnetic properties of [FeCoSiN/SiNx]18 multilayer thin films for applications in GHz range

[FeCoSiN/SiNx]18 multilayer thin films with different SiNx layer thickness (t) ranging from 0.75 to 4 nm were fabricated by reactive magnetron co-sputtering without applying an external induced magnetic field. The grain size, morphology, electrical properties, and static and dynamic magnetic properties of [FeCoSiN/SiNx]18 multilayer thin films were investigated systematically. The results indicated that SiNx layer thickness had a profound impact on the physical properties of the multilayer thin films. The in-plane uniaxial magnetic anisotropy field (from 114 ± 21 to 163 ± 14 Oe), ferromagnetic resonance frequency (from 4.09 to 4.64 GHz) and resistivity (from 188 to 333 μΩ cm) could be tailored effectively by adjusting the SiNx layer thickness from 0.75 to 4 nm. Moreover, when the SiNx layer thickness reached 2 nm, the continuous growth of FeCoSiN polycrystalline layers was to be interrupted completely and it would result in a minimum grain size of 4.9 ± 0.7 nm. The root mean square roughness of multilayer thin films also acquired a minimum value of 0.8 nm and the corresponding easy axis coercivity achieved a minimum value of 2.8 ± 0.1 Oe.