Magnetic Damping Modulation in ${\mathrm{IrMn}}_3/{\mathrm{Ni}}_{80}{\mathrm{Fe}}_{20}$ via the Magnetic Spin Hall Effect

Noncollinear antiferromagnets can have additional spin Hall effects due to the net chirality of their magnetic spin structure, which provides for more complex spin-transport phenomena compared to ordinary nonmagnetic materials. Here we investigated how ferromagnetic resonance of permalloy (${\mathrm{Ni}}_{80}{\mathrm{Fe}}_{20}$) is modulated by spin Hall effects in adjacent epitaxial ${\mathrm{IrMn}}_3$ films. We observe a large dc modulation of the ferromagnetic resonance linewidth for currents applied along the [001] ${\mathrm{IrMn}}_3$ direction. This very strong angular dependence of spin-orbit torques from dc currents through the bilayers can be explained by the magnetic spin Hall effect where ${\mathrm{IrMn}}_3$ provides novel pathways for modulating magnetization dynamics electrically.

Figure 1

(a) The schematic of the ${\mathrm{IrMn}}_3/{\mathrm{Ni}}_{80}{\mathrm{Fe}}_{20}$ (permalloy, Py) bilayer capped with a thin layer of Ti and also the unit cell of ${\mathrm{IrMn}}_3$ with its spin structure. Note that the Mn atoms in the unit cell of ${\mathrm{IrMn}}_3$ form a kagome lattice in the $\{111\}$ planes with the spins either pointing inwards or outwards in each triangular Mn arrangement. (b) The x-ray diffraction pattern measured for a 20-nm thick ${\mathrm{IrMn}}_3$ layer capped with a 2-nm Ti layer. (c) Measured magnetic hysteresis curves after field cooling in a magnetic field of $+70\mathrm{kOe}$ applied along either the [001] or [010] directions at a temperature of 300 K. (d) Magnetic hysteresis curves after field cooling in a magnetic field of $+70\mathrm{kOe}$ applied along the [100] direction at a temperature of 300 K. (e) Measured exchange bias field as a function of temperature after field cooling with an applied magnetic field of $+70\mathrm{kOe}$ along the [001] direction, showing that the blocking temperature of the ${\mathrm{IrMn}}_3(20\mathrm{nm})/{\mathrm{Ni}}_{80}{\mathrm{Fe}}_{20}(10\mathrm{nm})$ bilayer is 380 K.

Figure 2

(a) Schematic of the flip-chip ferromagnetic resonance measurement setup, where dc current (I) leads are connected to the Ti layer. (b) and (e) ferromagnetic resonance (FMR) signals obtained using a VNA for the magnetic field applied along the [001] and [011] crystallographic directions, respectively. (c) and (f) FMR frequency as a function of magnetic field, which was applied along the [001] and [011] crystallographic directions, respectively. The fits are performed with the Kittel equation, where $\gamma =g{\mu }_B/\hslash =2.8\mathrm{GHz}/\mathrm{kOe}$ and $4\pi M_{\text{eff}}=(9706\pm 1)\mathrm{Oe}$. (d) and (g) The linewidth variation as a function of the FMR frequency for the crystallographic directions [001] and [011], respectively.

Figure 3

Electric current modulation of FMR measured for $\mathrm{MgO}/{\mathrm{IrMn}}_3(20\mathrm{nm})/{\mathrm{Ni}}_{80}{\mathrm{Fe}}_{20}(10\mathrm{nm})/\mathrm{Ti}(2\mathrm{nm})$. (a) and (c) FMR linewidth variation as a function of the resonance frequency with dc currents of $\pm 1\mathrm{mA}$ applied along the [001] crystallographic direction and magnetic field applied along the [001] and [011] crystallographic directions, respectively. (b) and (d) Damping variation as a function of dc current for the [001] and [011] crystallographic directions, respectively.

Figure 4

(a) Schematic diagram of two chiral antiferromagnetic spin configurations (spins-in and spins-out) of the Mn moments in ${\mathrm{IrMn}}_3$. Because of the magnetic spin Hall effect, the trajectories of spin-up and spin-down electrons have opposite transverse components and produce a spin current in the [001] direction. The angular variation of the magnetic field ($H$) in the plane of the film is also shown and it determines the polarization of the spin accumulation due to the magnetic spin Hall effect. (b) Variation of the current dependent Gilbert magnetic damping as a function of the applied magnetic field angle, which in turn defines the polarization of the spin accumulation due to the magnetic spin Hall effect. The curves represent the function $\{[{\alpha }_{[011]}\text{−}\alpha (\phi )]/{\alpha }_{[011]}\}\times 100\%=\mathrm{\Delta }{\alpha }_{\mathrm{MSHE}}\sin (\pm 2\phi )$, with $\mathrm{\Delta }{\alpha }_{\mathrm{MSHE}}=(40\pm 1)\%$.