Exchange bias in Co/MnPt polycrystalline films on Si(100)/SiO2 substrates with Ta underlayer

Structure and magnetic properties of sputter-prepared Co(5 nm)/MnPt bilayer films with Ta underlayer and various thicknesses of MnPt layer (tMnPt) have been studied. Ta underlayer is effective in promoting the ordering of MnPt layer, flattening the surface and interface, and therefore leading to the improvement of the exchange bias field (HE). Nevertheless, higher annealing temperature leads to the interdiffusion and decrease HE. Besides, low HE of 8 kA/m with higher coercivity for the sample with thinner tMnPt = 10 nm might be related lower magnetic anisotropy energy for MnPt layer due to too thin antiferromagnetic layer, and therefore, HE is increased to 13.8-20.6 kA/m with increasing tMnPt to 30-100 nm. Larger grain size distribution and roughened interface found for the sample with thicker tMnPt = 100 nm may result in reduced HE. This study provides useful information to fabricate exchange-bias Co/L10-MnPt system.