Interdiffusion effect on exchange coupling in annealing NiFe/FeMn and FeMn/NiFe systems

The effect of interdiffusion on the exchange coupling field (H _ex) and coercivity (H_c) in annealing NiFe/FeMn and FeMn/NiFe systems was investigated in the study. Type I samples: Silicon substrate/Ta/NiFe/FeMn/Ta and Type II samples: Silicon substrate/Ta/FeMn/NiFe/Ta were prepared. Annealing was carried out at 200 to 450°C for two hours under 720 Oe, respectively. The results show that the Hex and Hc in two types samples were dependent on the annealing temperature. For both types the magnetization loss ratio (AM/MS) is negative, which reflects a loss of magnetization associated with interfacial mixing caused by annealing. The magnetization loss ratio becomes larger when the annealing temperature increases. The exchange coupling of these two types samples is associated with interfacial diffusion between the NiFe and FeMn interface. The annealing treatment also affected the H_c. In these two types samples, the exchange coupling was improved from modification of the interface between layers by annealing. The extended annealing (above 375°C) changes the exchange coupling in these two types samples due to serious interdiffusion of the interface between NiFe and FeMn layers. It results in unwanted interdiffusion effects at the interface and a concomitant reduction in the exchange bias field.