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 Angstrom Fe layers alternated by 30 Angstrom of V. This typical bilayer was repeated 15 times. The samples were structurally characterized by x-ray diffraction (XRD) in the (theta-2 theta) 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 Mossbauer spectroscopy (CEMS). This multilayer was annealed at temperatures between 550 and 670 degrees C for 60 minutes. The XRD result for the as-deposited multilayer shows a high-degree crystallinity, while GEMS 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 (alpha phase) into a tetragonal structure (sigma phase). GEMS results show a magnetic moment reduction for temperatures above 640 degrees C and an order-disorder transition. The magnetic measurements suggest also a phase transformation.