Exchange coupling of bilayers and synthetic antiferromagnets pinned to MnPt

Exchange bias and blocking temperature were studied in MnPt based bottom-pinned bilayers and synthetic antiferromagnets (SAF) prepared by magnetron sputtering. The structure and magnetic properties were determined as a function of the MnPt layer thickness. Exchange coupling was found to be ($J_{ex} = 0.4$ erg/cm$^{2})$ for a MnPt ($t \le 20$ nm)/CoFe (5 nm) bilayer. The distribution of the blocking temperature TB was analyzed and its width $\Delta T_{B}$ and center point $T_{B,\,center}$ determined. TB is about 280 $^{\circ}$C for thinner MnPt films, and increases to 330 °C for thick films. $\Delta T _{B}$ is constant for thick MnPt but steadily increases as the thickness decreases. SAF structures show higher exchange bias and higher $T_{B,\,center}$ at thin layer thickness ($t_{\rm MnPt }= 8.5$ nm) compared to bilayers