High-frequency magnetoelastic measurements on Fe-Co-Hf-N/Ti-N multilayer coatings

Fe32Co44Hf12N12/Ti50N50 multilayer films with seven bilayers and a total thickness of about 1 μm were grown by a sequential deposition of Fe32Co44Hf12N12 and Ti50N50 individual layers by means of reactive DC and RF magnetron sputtering, respectively. Additionally, a Fe32Co44Hf12N12 monolayer coating with a thickness of about 500 nm was deposited in order to determine the magnetic properties of the single layer. The films were investigated with respect to their static and dynamic ferromagnetic properties. A uniaxial anisotropy field of 5 mT could be induced after annealing the multilayer films for 1 h at 400 °C in vacuum in a static magnetic field of 50 mT. Additionally, magnetic softness (μ0Hc=0.6 mT) and cut-off frequencies above 2 GHz were observed. Inducing compressive stress increases the cut-off frequency of the Fe32Co44Hf12N12 single layer as well as of the Fe32Co44Hf12N12/Ti50N50 multilayer films whereas tensile stress causes a decrease in the cut-off frequency. Accordingly, the dependence of the cut-off frequency on external mechanical stress is theoretically described. Furthermore, the possibility of detecting mechanically induced stress in a ferromagnetic layer was demonstrated by the shift of the cut-off frequency with a resolution of 1.0 MPa.