Interlayer exchange coupling dependence of thermal stability parameters in synthetic antiferromagnetic free layers

We conducted a detailed comparative study of thermal stability properties over a thermal excitation of switching of the free layer in a magnetic tunnel junction (MTJ) with Ni81Fe19, Co90Fe10, and synthetic antiferromagnetic (Syn-AF) free layers with several strengths of interlayer exchange coupling (JEX). The thermal stability properties were investigated using the junction magnetoresistance of current-perpendicular MTJ devices with a word line as probes. The observed sweep-rate-dependent coercivities were analyzed using the Sharrock formula. The results confirmed strong JEX dependence on thermal stability parameters (KuV/kT)(KuV/kT) in Syn-AF free layers. The values of KuV/kBTKuV/kBT for MTJs with Syn-AF free layers decreased with a decrease in the strength of JEX, and the increase in the effective volume of the Syn-AF free layer disappeared at JEX⩽0.52erg/cm2. The Syn-AF free layer with JEX>0.52 erg/cm2 is relevant for high-density spin electronic nanodevices with a low aspect ratio.