Interfacial Dzyaloshinskii-Moriya Interaction: Effect of $5d$ Band Filling and Correlation with Spin Mixing Conductance

The Dzyaloshinskii-Moriya interaction (DMI) at the heavy metal (HM) and ferromagnetic metal (FM) interface has been recognized as a key ingredient in spintronic applications. Here we investigate the chemical trend of DMI on the $5d$ band filling ($5d^3–5d^{10}$) of the HM element in HM/FM $(\mathrm{FM}=\mathrm{CoFeB},\mathrm{Co})/\mathrm{MgO}$ multilayer thin films. DMI is quantitatively evaluated by measuring asymmetric spin wave dispersion using Brillouin light scattering. Sign reversal and 20 times modification of the DMI coefficient $D$ have been measured as the $5d$ HM element is varied. The chemical trend can be qualitatively understood by considering the $5d$ and $3d$ bands alignment at the HM/FM interface and the subsequent orbital hybridization around the Fermi level. Furthermore, a correlation is observed between DMI and effective spin mixing conductance at the HM/FM interfaces. Our results provide new insights into the interfacial DMI for designing future spintronic devices.

Figure 1

(a) Schematics of BLS measurement geometry. (b) BLS spectra (with 100 MHz interchannel frequency separation) for DE spin waves recorded at a fixed incident angle $k=13.9\mathrm{rad}/\mu \mathrm{m}$ under oppositely oriented external magnetic fields $\mathbf{H}=2k\mathrm{Oe}$ in $\mathrm{Pt}/\mathrm{CoFeB}/\mathrm{MgO}$ sample. The solid lines represent fittings with Lorentzian functions.

Figure 2

(a) The dependence of spin wave frequency $f(k=0)$ on $H$ in CoFeB samples with different underlayers. The solid lines are fittings with Eq. (1) under $k=0$. (b) Simulation results of $ϵ(K_{\perp },k)-ϵ(K_{\perp },-k)$.

Figure 3

(a),(b) The linear dependence of $\mathrm{\Delta }f$ on $k$ in CoFeB samples with different underlayers. (c),(d) The $D_S$ values determined at CoFeB and Co samples with different underlayers. The black lines serve as visual guides.

Figure 4

(a),(b) The dependence of spin wave resonance linewidth FWHM on $H$ in CoFeB samples with different underlayers. (c) An observed correlation between $|D_{\mathit{S}}|$ and $g_{\mathrm{eff}}^{\uparrow \downarrow }$. The dashed line is a quadratic function for visual guide [45]. (d) The $D$ (red) and linewidth FWHM (black) as a function of $1/t(\mathrm{CoFeB})$ in $\mathrm{Ir}/\mathrm{CoFeB}(\text{wedge})/\mathrm{MgO}$ sample at $H=2\mathrm{kOe}$. The solid lines are the least square fits.