Optimizing magnetic damping in Fe-Co based ferromagnetic alloys

Magnetic damping is central to the performance of ferromagnetic materials in many applications. In metallic ferromagnets, the damping can be due to electronic excitations, as well as due to coupling to the lattice. Previously, it has been demonstrated that Fe₇₅Co₂₅ has ultralow magnetic damping [1], since the composition has the lowest electronic density of states. It has also been shown that the magnetic damping in Fe₅₀Co₅₀ alloys can be reduced by the addition of carbon [2], which results in a structural transformation to an amorphous phase and thereby reduces the coupling of the magnetization dynamics to the lattice. Here, we combine the two strategies and investigate whether the same structural transformation can further reduce the magnetic damping of (Fe₇₅Co₂₅)_1-xB_x. Magnetometry measurements show a strongly reduced coercivity at around x ≈ 5% and we also characterize the structural transition via transmission electron microscopy and the magnetic damping via broadband ferromagnetic resonance.

[1] M.A.W. Schoen et al., Nat. Phys. 12, 839-842 (2016)

[2] J. Wang et al., Phys. Rev. Appl. 12, 034011 (2019)