Exchange bias study of sub-100 nm-diameter CoFeB/IrMn antidot and nanodot arrays fabricated by nanosphere lithography

Exchange-coupled bilayers are widely used as pinned layers in nanometric spintronic devices. In this work, sub-100 nm-diameter CoFeB/IrMn antidot and nanodot arrays were patterned by nanosphere lithography. The exchange bias (Hex) and coercivity (Hc) of the nanostructures and continuous films exhibit similar exponential dependence on CoFeB layer thickness. Magnetic field annealing results in changed crystallinity, surface roughness, and magnetic properties. Reduced Hc and enhanced Hex are observed after annealing at low temperatures, while high-temperature annealing results in higher Hc and lower Hex. This work provides physical insights on the magnetization reversal response in nanosized spintronic devices involving CoFeB/IrMn reference layers.