Effects of sputtering Ar gas pressure in the exchange stiffness constant of Co₄₀Fe₄₀B₂₀ thin films

The exchange stiffness constants of 25-nm-thick Co₄₀Fe ₄₀B₂₀ films are investigated by Brillouin light scattering. Series of Co₄₀Fe₄₀B₂₀ films is prepared with various Ar gas pressures, and we found that the exchange stiffness constant decreases from 1.41 to 0.98×10^-11 1rom 1.41 to 0.98ous Ar gas pressures, and we found that thin stiffness constants are much smaller than CoFe values due to the B atoms, and the dependence of Ar gas pressure is noticeable. Based on our previous theoretical work, the switching current density of spin transfer torque magnetic random access memory is very sensitive on the exchange stiffness constant; it implies that engineering the exchange stiffness constant by the fabrication process is important to reduce switching current density and the dispersion of switching current density.