Interdiffusion and exchange bias in the MnxPt1-x/Co system

MnxPt1-x(25 nm)/Co(8.0 nm) antiferromagnetic/ferromagnetic (AF/F) bilayers were grown via dc magnetron sputtering at room temperature on Si(111) substrates. Samples were annealed in a vacuum in a 1200 Oe magnetic field at various temperatures T-A after growth. The Mn concentration x was determined from the MnPt lattice parameters and Rutherford backscattering spectroscopy. The maximum exchange bias (H-E) was observed for xsimilar to0.50, in agreement with previous work. Annealing caused the MnPt to form an ordered face-centered-tetragonal CuAu ordered structure which is necessary to observe H-E. However, x-ray reflectivity indicates that an interdiffusion region exists at the MnPt/Co interface. The interdiffusion increases with T-A, resulting in lower H-E. The T-A that maximizes H-E, 318 degreesC, is a compromise between the volume fraction of MnPt forming the ordered CuAu structure, which increases H-E, and the amount of interdiffusion, which decreases H-E. (C) 2003 American Institute of Physics.