Thermal annealing effects on the structural and magnetic properties of Fe/V multilayers

We report a study on the structural and magnetic properties of iron-vanadium thin films grown in multilayer form and mixed by thermal treatment. The multilayer was composed of 30 Å Fe layers alternated by 30 Å of V. This typical bilayer was repeated 15 times. The samples were structurally characterized by x-ray diffraction (XRD) in the (θ-2θ) geometry. The magnetic characterization was made using a conventional alternate gradient magnetometer (AGM) with the magnetic field applied along the plane of the film, and by conversion electron Mössbauer spectroscopy (CEMS). This multilayer was annealed at temperatures between 550 and 670 °C for 60 minutes. The XRD result for the as-deposited multilayer shows a high-degree crystallinity, while CEMS suggests an abrupt interface, since no significant contribution from vanadium in iron is observed. After the thermal treatment, the results from XRD show a phase transformation of the bcc-disordered structure (α phase) into a tetragonal structure (σ phase). CEMS results show a magnetic moment reduction for temperatures above 640 °C and an order-disorder transition. The magnetic measurements suggest also a phase transformation.