Dzyaloshinskii-Moriya Interaction across an Antiferromagnet-Ferromagnet Interface

The antiferromagnet- (AFM-)ferromagnet (FM) interfaces are of central importance in recently developed pure electric or ultrafast control of FM spins, where the underlying mechanisms remain unresolved. Here we report the direct observation of an Dzyaloshinskii-Moriya interaction (DMI) across the AFM-FM interface of $\mathrm{IrMn}/\mathrm{CoFeB}$ thin films. The interfacial DMI is quantitatively measured from the asymmetric spin-wave dispersion in the FM layer using Brillouin light scattering. The DMI strength is enhanced by a factor of 7 with increasing IrMn layer thickness in the range of 1–7.5 nm. Our findings provide deeper insight into the coupling at the AFM-FM interface and may stimulate new device concepts utilizing chiral spin textures such as magnetic Skyrmions in AFM-FM heterostructures.

Figure 1

(a) Schematics of BLS experiment and possible atomic arrangement at the interface. (b) BLS spectra for DE spin waves recorded at a fixed incident angle with $k=16.7\mathrm{rad}/\mu \mathrm{m}$ under oppositely oriented external magnetic fields $\mathbf{H}$. The solid lines represent fittings with Lorentzian functions.

Figure 2

(a) The asymmetric spin wave dispersion under oppositely oriented $\mathbf{H}$ at $\mathrm{IrMn}(5)/\mathrm{CoFeB}(2)$. Solid lines refer to fitting with Eq. (1). (b) The linear dependence of $f_{\mathrm{dm}}$ on $k$ in $\mathrm{IrMn}(5)/\mathrm{CoFeB}(2)$ (red) and $\mathrm{Ir}(5)/\mathrm{CoFeB}(1.2)$ (black) samples. (c) The $D$ as a function of $1/t_{\text{CoFeB}}$ at $\mathrm{Ir}\text{Mn}/\mathrm{CoFeB}(\text{wedge})/\mathrm{MgO}$. The solid lines refer to the least square fits.

Figure 3

(a) The linear dependence of $f_{\mathrm{dm}}$ on $k$ for a series of $\mathrm{IrMn}/\mathrm{CoFeB}(2)$ thin films with different IrMn thicknesses. (b) The magnitude of the DMI coefficient $D$ increases with larger IrMn thickness. The negative value of $D$ shows that left-handed chirality is favored in this material system.