Detection and In Situ Switching of Unreversed Interfacial Antiferromagnetic Spins in a Perpendicular-Exchange-Biased System

By using the perpendicular-exchange-biased $\mathrm{Pt}/\mathrm{Co}/\alpha \mathrm{\text{−}}{\mathrm{Cr}}_2{\mathrm{O}}_3$ system, we provide experimental evidence that the unreversed uncompensated Cr spins exist at the $\mathrm{Co}/\alpha \mathrm{\text{−}}{\mathrm{Cr}}_2{\mathrm{O}}_3$ interface. The unreversed uncompensated Cr spin manifests itself in both the vertical shift of an element-specific magnetization curve and the relative peak intensity of soft-x-ray magnetic circular dichroism spectrum. We also demonstrate an in situ switching of the interfacial Cr spins and correspondingly a reversal of the exchange bias without interfacial atomic diffusion. Such switching shows the direct relationship between the interfacial antiferromagnetic spins and origin of the exchange bias. The demonstrated switching of exchange bias would likely offer a new design of advanced spintronics devices, using the perpendicular-exchange-biased system, with low power consumption and ultrafast operation.

Figure 1

(a) RHEED pattern of the $\alpha \mathrm{\text{−}}{\mathrm{Cr}}_2{\mathrm{O}}_3(0001)$ layer. The azimuth direction of the electron incidence was [$11\overline{2}0$] of the $\alpha \mathrm{\text{−}}{\mathrm{Al}}_2{\mathrm{O}}_3(0001)$ substrate. (b) Cross-sectional high-resolution TEM images. The direction of the electron incidence was [$11\overline{2}0$] of the $\alpha \mathrm{\text{−}}{\mathrm{Al}}_2{\mathrm{O}}_3(0001)$ substrate. The inset shows the FFT image of the $\alpha \mathrm{\text{−}}{\mathrm{Cr}}_2{\mathrm{O}}_3(0001)$ lattice.

Figure 2

(a) XAS, XMCD spectra measured at 180 K after cooling the sample in the $+0.4\mathrm{T}$ magnetic field at Co $L_{2,3}$ and Cr $L_{2,3}$ edges. Red (black) and blue (dark gray) lines represent the absorption spectra for the positive and negative helicities, respectively, of the incident photons. Green (light gray) curves represent the XMCD spectrum. (b),(c) ESMCs for Co and Cr measured at (b) 235 K and (c) 180 K. Red small (blue large) lines represent the curves for Co (Cr), respectively. The ESMC for Co shown here is the difference curve at energy positions $L_3$ and $L_2$, and the ESMC for Cr is the difference curve at energy positions B and C labeled in the XMCD spectrum.

Figure 3

ESMCs for Cr $L_3$ edge measured at (a) 230 K and (b) 180 K. Red (black) and blue (dark gray) curves correspond to the curves acquired after cooling the sample in the positive and negative fields, respectively. XMCD spectrum for Cr $L_{2,3}$ edges measured at 180 K after cooling the sample in the (c) positive and (d) negative magnetic fields. Red (black) and blue (dark gray) curves correspond to the spectra measured at $+1.0\mathrm{T}$ and $-1.0\mathrm{T}$, respectively.

Figure 4

Left figure represents the spin configuration after the field-cooling in the negative magnetic field. Right figure represents the spin configuration after the FM magnetization reversal. Red or dark gray arrows represent the FM spins. Blue or black (green or light gray) arrows represent the up (down) AFM spins. The dotted lines in the right figure represent the original orientation of the AFM spins. ${\theta }_i$ ($i=1,2,3\dots$) represents the canting angle of the AFM spin.