Annealing effect on an exchange‐biasing Co/IrMn system

Abstract

The top-configuration Co(y)/IrMn(90 Å) exchange-biasing phenomenon has been studied by sputtering method with two conditions: (a) the substrate temperature (T s ) was kept at room temperature (RT) only, and (b) T s = RT with an in-plane field (h) = 500 Oe deposition and postdeposition annealing in the field at T A = 250 °C for 1 h, with the samples field cooled to RT. High resolution electron cross-sectional transmission electron microscopy (HR X-TEM) reveals that the IrMn (111) texturing plays a main role to exchange-biasing field (H ex ) and interfacial energy (J k ). The H ex versus y result shows that H ex increases when y decreases in case (b). Since J k = H ex M s y, where M s is Co magnetization, it is easy to derive H ex = J k /(M s y). Therefore, if H ex is inversely proportional to y, with J k /M s constant, we find H ex y = constant. In case (a), H ex is very small in general, while in case (b), H ex is of the order of 60-180 Oe. Moreover, the y dependence of J k is similar to that of M s for each curve. Finally, the H c is inversely proportional to y because of the surface pinning effects from the Ta/Co and Co/IrMn interfaces.