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

Mckinnon, T.; Hübner, R.; Heinrich, B.; Girt, E.
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 0.45 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)/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.

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Permalink: https://www.hzdr.de/publications/Publ-30731
Publ.-Id: 30731