Effect of Ir–Mn composition on exchange bias and thermal stability of spin valves with nano-oxide layers

Abstract

The Ir–Mn bottom-pinned spin valves with nano-oxide layers (NOLs), Ta∕Ni81Fe19∕Ir–Mn∕Co90Fe10∕NOL∕Co90Fe10∕Cu∕Co90Fe10∕NOL∕Ta, were fabricated by dc magnetron sputtering. The magnetoresistance (MR), magnetization, and exchange bias have been studied as a function of Ir–Mn composition and annealing temperature. It was observed that the spin valves with the Ir–Mn layer containing relatively low Mn content (58.9–72.4at.% Mn) show the best thermal endurance. For these samples, the Mn diffusion is effectively hampered by the NOL with a large MR value of about 12.5% even after annealing at 300°C. On the other hand, the exchange bias field of the pinned CoFe layer shows a maximum at Mn content of about 72.4at.%, which is different from the widely adopted composition, Ir-80at.% Mn, optimized from the top-pinned NiFe∕Ir–Mn system. Moreover, the blocking temperature of the Ir–Mn∕CoFe system with 72.4at.% Mn is higher than that with 80.6at.% Mn. The present results suggest that the Ir–Mn∕CoFe pinning system with Mn content at about 72% renders the most favorable exchange bias and the best thermal stability for the bottom-pinned specular spin valves.