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

Mn x Pt 1−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 TA after growth. The Mn concentration x was determined from the MnPt lattice parameters and Rutherford backscattering spectroscopy. The maximum exchange bias (HE) was observed for x∼0.50, in agreement with previous work. Annealing caused the MnPt to form an ordered face-centered-tetragonal CuAu ordered structure which is necessary to observe HE. However, x-ray reflectivity indicates that an interdiffusion region exists at the MnPt/Co interface. The interdiffusion increases with TA, resulting in lower HE. The TA that maximizes HE, 318 °C, is a compromise between the volume fraction of MnPt forming the ordered CuAu structure, which increases HE, and the amount of interdiffusion, which decreases HE.