Composition dependence of exchange stiffness in FexPt1-x alloys

The exchange stiffness constants of chemically disordered FexPt1-x films with thickness around 50 nm were determined by means of ferromagnetic resonance. It was found to increase with increasing Fe content from 6 +/- 4 pJ/m for x=0.27 to 15 +/- 4 pJ/m for x = 0.67. Theoretical results from fully relativistic and scalar-relativistic band-structure calculations using the Korringa-Kohn-Rostoker method confirm the experimentally obtained values. In addition, determination of the magnetocrystalline anisotropy by angular-dependent measurements of the ferromagnetic resonance gave the possibility to estimate the exchange length that was found to be 40-50 nm for all compositions investigated in this work.