The role of boron on exchange coupling in NiFe/Ru1- xBx/FeCo trilayer structures

Abstract

In this work, we study the interlayer exchange coupling, J, between two NiFe and FeCo layers in a series of NiFe / Ru 1 - x B x (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 0.45 nm for 5% and 10% B and thinner than 0.525 nm 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 (2.5 nm) / NiFe (0.8 nm) / Ru 1 - x B x(23 nm) layer structure. We find that after annealing at 250 ° C, the sample containing 15% B within the Ru 85 B 15 layer had significantly more diffusion of Fe into the Ru 85 B 15 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.