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

Abstract

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 (∆M/M S ) 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.

Influence of temperature on thermal relaxation of exchange bias field in CoFe/Cu/CoFe/IrMn spin valve*

“…The surface/interface R rms increases with the temperature rising after the spin valve has been heated. This is consistent with the conclusion obtained by Chen et al, [17] in which the roughness of NiFe/FeMn bilayer increases with the temperature rising. Figure 3 shows that the shape of the hysteresis loop of the CoFe/Cu/CoFe/IrMn spin valve changes greatly with the increase of temperature.…”

“…Roughness is also an important factor that affects exchange bias. [17][18][19] Generally, the exchange bias field decreases upon increasing the roughness; [20,21] therefore, the increased surface/interface roughness after heating at 150 • C and 275 • C is another major reason for the reduction in the multilayer exchange bias field of the spin valves.…”

Top and Bottom Spin Valves With Ni-Fe-Mn Antiferromagnetic Layer

“…Notably, the permalloy layer should be deposited on manganese or the manganese containing alloy [1]. With this deposition order, the authors of [2] fixed the high value H ex = 110 Oe after the annealing of the FeMn(15nm)/NiFe(15nm) bilayers. It should be noted that the formation of this ordered system is only possible with the thermal treatment of the films that contain the permalloy and manganese layers or the layers of the manganese containing alloy.…”