Effect of thermal annealing on structure and magnetic properties in a Ni-Cr multilayer

Evolution of structural and magnetic properties in a nickel/chromium (Ni/Cr) multilayer, as a function of different annealing temperatures was investigated. The Ni/Cr multilayer of nominal structure [Cr (50 Å)/Ni (50 Å)]×10/Cr (30 Å) was grown on a Si substrate by radio frequency ion beam sputtering at room temperature. X-ray diffraction, X-ray reflectometry, atomic force microscopy and crossectional scanning electron microscopy were employed for the complete structural characterization of the multilayer whereas superconducting quantum interference device vibration sample magnetometer was used for the bulk magnetisation study. The effect of in-situ and ex-situ annealing on overall structural property of the multilayer also reported in present work. From in-situ X-ray reflectometry (50-400 °C), 300 °C was detected as the optimum temperature for improved structural properties of the Ni/Cr multilayer. Initiation of alloying in the multilayer sample was noticed at 350 °C. The multilayer found to exhibit polycrystalline nature observed by X-ray diffraction. Total thickness of the multilayer system was confirmed by crossectional scanning electron microscopy and in well agreement with X-ray reflectivity results. The Ni/Cr sample found to exhibit soft ferromagnetic behaviour after annealing at 300 °C and 400 °C. However the net magnetic moment reduced upon annealing at higher temperature (400 °C).