Current switching of the antiferromagnetic Néel vector in Pd/CoO/MgO(001)

Recently, the electrical switching of antiferromagnetic (AFM) order has been intensively investigated because of its application potential in data storage technology. Herein, we report the current switching of the AFM Néel vector in epitaxial Pd/CoO films as a function of temperature. Using combined measurements of Hall resistance (HR) and x-ray magnetic linear dichroism (XMLD) below and above the AFM Néel temperature, we unambiguously identified both magnetic and nonmagnetic contributions to the current-induced HR change. Through magnetic field-induced HR measurements, we quantitatively determined the percentage of current-induced CoO spin switching. Further, we showed that the thermal effect dominated the CoO magnetic switching more in samples with a thinner Pd layer and that samples with a thicker CoO layer required higher thermal activation for current-induced magnetic switching. These results provide a clear and comprehensive picture of current-induced AFM spin switching across the AFM Néel temperature.

Figure 1

(a) A schematic of current switching and XMLD measurements on the eight-terminal Hall bar structure of the Pd(10-nm)/CoO(2.5-nm)/MgO(001) sample. The width is 20 μm for the writing pulse current path along the easy magnetization axes of CoO[110] ($x$-axis) and CoO $\left[1\overline{1}0\right]$ ($y$-axis), and 5 μm for the reading current (1 mA) path along the diagonal directions. (b) LEED patterns of the CoO film and MgO(001) substrate. (c) The HR change as a function of the current pulse number. The direction of the current pulse changes after every five pulses, as depicted by the red and purple arrows in (a). (d) CoO spectra measured with linear polarization of the x-ray parallel and perpendicular to the $x$-axis, and the corresponding XMLD between the two polarizations. All measurements were performed at RT, which is higher than the CoO Néel temperature.

Figure 2

(a) HR as a function of increasing $H_x$ after field cooling (FC) with $H_{\mathrm{FC},y}=9\mathrm{T}$ at various temperatures across the CoO Néel temperature. (b) HR change and spin flop field as a function of temperature extracted from (a). HR change as a function of increasing $H_x$ (or $H_y$) after FC with (c) $H_{\mathrm{FC},y}=0.4\mathrm{T}$ or 9 T, or (d) $H_{\mathrm{FC},x}=0.4\mathrm{T}$ or 9 T. (e) HR change during field scanning normalized with $\mathrm{\Delta }{R}_{\mathrm{Hall}}$ using a FC of 9 T as a function of FC strength. Field-dependent measurements in (c) and (d) were performed at 250 K.

Figure 3

(a) HR change as a function of the current pulse number. The direction of the current pulse changes after every five pulses, as depicted by the red and purple arrows in Fig. 1. (b) CoO spectra measured with linear polarization of the x-ray parallel to the CoO[110] and $\mathrm{CoO}\left[1\overline{1}0\right]$ directions. The corresponding XMLD (c) before and (d) after the current pulse along the CoO[110] (the $x$-axis). (e) X-ray polarization angle $\varphi$ dependence of the CoO $R_{L3}$ ratio collected from both the big electrode and the Hall bar center. (f) The HR change in a four-terminal Hall bar structure as a function of current pulse number with $H=13\mathrm{T}$ applied along the CoO[110] direction (hollow symbols) and $H=0\mathrm{T}$ (solid symbols). All measurements were performed at 200 K.

Figure 4

(a) HR change as a function of increasing $H_x$ after FC ($H_{\mathrm{FC},y}=9\mathrm{T}$) and ($H_{\mathrm{FC},x}=9\mathrm{T}$) plus a current pulse applied along the $y$-axis ($I_{\mathrm{pulse},y}=100\mathrm{mA}$) and the $x$-axis ($I_{\mathrm{pulse},x}=100\mathrm{mA}$), respectively. (b) HR change as a function of increasing $H_y$ after FC ($H_{\mathrm{FC},x}=9\mathrm{T}$) and ($H_{\mathrm{FC},y}=9\mathrm{T}$) plus a current pulse applied along the $y$-axis ($I_{\mathrm{pulse},y}=100\mathrm{mA}$). All measurements were performed at 250 K.

Figure 5

(a) Current pulse-induced HR changes at 90 mA for 200, 230, 250, and 270 K, and at 85 mA for 300 K from a Pd(10-nm)/CoO(2.5-nm) sample. (b) Current pulse-induced HR change at 42 mA for 200, 230, 250, and 270 K, and at 40 mA for 290 K from a Pd(5-nm)/CoO(2.5-nm) sample. (c) Selected $\mathrm{\Delta }{R}_{\mathrm{Hall}}$ signal as a function of current pulse number at 230 K from the Pd(5-nm)/CoO(2.5-nm) sample. (d) Summary of the $\mathrm{\Delta }{R}_{\mathrm{Hall}}$ amplitude as a function of current pulse density at various temperatures from the Pd(5-nm)/CoO(2.5-nm) sample. (e) Current pulse-induced HR change at 46 mA for 200, 230, 250, 270, and 290 K, and at 45 mA for 300 K from a Pd(5-nm)/CoO(10-nm) sample. (f) Selected $\mathrm{\Delta }{R}_{\mathrm{Hall}}$ signal as a function of current pulse number from the Pd(5-nm)/CoO(10-nm) sample at 290 K. The Hall bar width of the writing current pulse is 20 μm for all panels.