Annealing effect on an exchange-biasing Co/IrMn system

摘要

The top-configuration Co(y)/IrMn(90 A) 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 ℃ 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_sy, where M_s is Co magnetization, it is easy to derive H_(ex) = J_k/(M_sy). 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.