Low-Damping Vertically Graded Ferromagnetic Films*

Recent studies indicate that ~10-nm-thick ferromagnetic films with vertical compositional gradients can produce strong spin-orbit torques (SOTs). Such graded films are of technological interest since they are more thermally stable than ultrathin magnetic films in typical SOT devices. An important unanswered question is whether graded magnetic films can possess low damping, which is vital for minimizing the input power for precessional SOT devices.

We show that vertically graded ferromagnetic films exhibit low effective damping, comparable to homogeneous films of low-damping Co₂₅Fe₇₅[1] and Fe₈₀V₂₀[2]. Vertically graded films (thickness ~10 nm) of polycrystalline Co₂₅Fe₇₅-Fe₈₀V₂₀ were grown by continuously tuning the sputtering powers on Co₂₅Fe₇₅ and Fe₈₀V₂₀ targets. The FMR linewidths of graded Co₂₅Fe₇₅-Fe₈₀V₂₀ films are only <25% greater than those of homogeneous Co₂₅Fe₇₅. Thus, we find that the intentional inhomogeneity in the graded films does not lead to large linewidth broadening. Our results demonstrate vertically graded ferromagnetic films as promising candidates for power-efficient SOT devices.

 

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

[2] D. A. Smith, et al. Phys. Rev. Appl. 14, 034042 (2020)