Domain-wall pinning, nonadiabatic spin-transfer torque, and spin-current polarization in permalloy wires doped with vanadium

Using pulsed-current measurements we investigate the domain-wall depinning via spin-transfer torque from pinning potentials in V-doped ${\text{Ni}}_{80}{\text{Fe}}_{20}$ wires. The domain-wall depinning boundary, showing the variation of threshold current density with longitudinal magnetic field is measured and reproduced using micromagnetic simulations. This method allows us to determine the spin-current polarization and nonadiabaticity parameter in these materials. By increasing the V concentration we show that the nonadiabaticity parameter is increased while the Gilbert damping is unaffected. On the other hand the spin-current polarization is decreased, resulting in larger threshold current densities.

Figure 1

(Color online) PEEM images and micromagnetic simulations showing equilibrium pinning states for a domain wall in (a) ${\text{Py}}_{99}{\text{V}}_1$, (b) ${\text{Py}}_{97.5}{\text{V}}_{2.5}$, and (c) ${\text{Py}}_{90}{\text{V}}_{10}$.

Figure 2

(Color online) (a) VSM measurements of 20 nm V-doped permalloy thin films with Bloch law fits showing normalized saturation magnetization as a function of temperature and (b) Gilbert damping parameter as a function of V concentration in 20 nm V-doped thin films, showing experimental error margins.

Figure 3

(Color online) (a) Experimental depinning boundaries for V-doped permalloy wires (points) and best-fit simulated depinning boundaries, respectively (solid lines). In the inset $\beta$ (solid circles) and $P$ (empty circles) are plotted as functions of V content. (b) Fitting coefficients (solid points) and best-fit spin-current polarization (empty points) as functions of nonadiabaticity parameter.