Absence of Evidence of Electrical Switching of the Antiferromagnetic Néel Vector

Much theoretical and experimental attention has been focused on the electrical switching of the antiferromagnetic (AFM) Néel vector via spin-orbit torque. Measurements employing multiterminal patterned structures of $\mathrm{Pt}/\mathrm{AFM}$ show recurring signals of the supposedly planar Hall effect and magnetoresistance, implying AFM switching. We show in this Letter that similar signals have been observed in structures with and without the AFM layer, and of an even larger magnitude using different metals and substrates. These may not be the conclusive evidence of spin-orbit torque switching of AFM, but the thermal artifacts of patterned metal structure on substrate. Large current densities in the metallic devices, beyond the Ohmic regime, can generate unintended anisotropic thermal gradients and voltages. AFM switching requires unequivocal detection of the AFM Néel vector before and after SOT switching.

Figure 1

Schematics of the eight-terminal patterned structure with the pulsed writing current along the 45° (write 1) and the 135° (write 2) lines for (a) planar Hall and (b) longitudinal resistance measurements. Relative changes of Hall resistance ($\mathbf{\Delta }{R}_{XY}$) in (c) $\mathrm{Pt}/\mathrm{NiO}/\mathrm{Si}$ and (e) $\mathrm{Pt}/\mathrm{NiO}/\mathrm{glass}$ and relative change of longitudinal resistance ($\mathbf{\Delta }{R}_{XX}$) in (d) $\mathrm{Pt}/\mathrm{NiO}/\mathrm{Si}$ and (f) $\mathrm{Pt}/\mathrm{NiO}/\mathrm{glass}$, after applying 10-ms writing current pulses alternately along the 45° and the 135° lines.

Figure 2

(a) $R_{XY}$ and (b) $\mathbf{\Delta }{R}_{XY}$ in $\mathrm{Pt}/\mathrm{NiO}/\mathrm{Si}$ as a function of one-shot writing current pulses along the 45° (write 1) or the 135° (write 2) lines. (c) $R_{XX}$ and (d) $\mathbf{\Delta }{R}_{XX}$ in $\mathrm{Pt}/\mathrm{NiO}/\mathrm{Si}$ as a function of one-shot current pulse along the 45° (write 1) or the 135° (write 2) lines.

Figure 3

The values of $\mathbf{\Delta }{R}_{XY}$ and $\mathbf{\Delta }{R}_{XY}$ after applying successive writing pulses current alternately along the 45° and the 135° lines for (a) $\mathrm{Pt}/\mathrm{Si}$, (b) $\mathrm{Pt}/\mathrm{MgO}$, and (c) $\mathrm{Pt}/\mathrm{glass}$; and for (d) $\mathrm{Pt}/\mathrm{Si}$, (e) $\mathrm{Pt}/\mathrm{MgO}$, and (f) $\mathrm{Pt}/\mathrm{glass}$, respectively, without any AFM.

Figure 4

Simulation of temperature distribution for the eight-terminal patterned $\mathrm{Pt}/\mathrm{glass}$ structure after applying one-shot current of density $1.75\times {10}^7\mathrm{A}/{\mathrm{cm}}^2$ along (a) 45° (write 1) and (c) 135° (write 2) lines. Simulation of Hall signal induced after one-shot writing current along (b) 45° (write 1) and (d) 135° (write 2) lines with the relative Seebeck coefficient of $8\mu \mathrm{V}/\mathrm{K}$. (e) The temperature difference between $T_1$ and $T_2$ and (f) $R_{XY}$ as a function of one-shot current pulse along 45° (write 1) and (c) 135° (write 2) lines.