The role of boron on exchange coupling in NiFe/Ru_1−xB_x/FeCo trilayer structures Available to Purchase

In this work, we study the interlayer exchange coupling, J, between two NiFe and FeCo layers in a series of $NiFe/Ru1−xBx(d)/FeCo$ synthetic antiferromagnet (SAF) samples, where the thickness of the spacer layer, d, is varied from 0.4 nm to 0.9 nm, and the boron concentration, x, is varied from 0 to 15 at. %. The samples are studied as deposited and after being annealed at $250°C$⁠. B is deposited into the Ru spacer layer to investigate what occurs after annealing a FeCoB/Ru/FeCoB SAF structure, which is commonly used in modern nanoscale magnetic devices, in which the FeCoB layer crystallizes to FeCo and B diffuses to adjacent layers. We find that J in as-deposited samples is relatively unaffected by adding up to 15% B into the Ru spacer layer. However, after annealing at $250°C$⁠, J changes the sign from antiferromagnetic coupling to ferromagnetic coupling for spacer layers thinner than $0.45nm$ for 5% and 10% B and thinner than $0.525nm$ for 15% B. We used transmission electron microscopy energy-dispersive x-ray spectroscopy in order to investigate the diffusion of atoms within a similar $Ta(2.5nm)/NiFe(0.8nm)/Ru1−xBx$(23 nm) layer structure. We find that after annealing at $250°C$⁠, the sample containing 15% B within the $Ru85B15$ layer had significantly more diffusion of Fe into the $Ru85B15$ layer, from the NiFe layer, as compared to the sample with 0% B. Thus, the presence of B within the spacer layer enhances diffusion of Fe into the spacer layer.