Anomalous Hall effect in antiferromagnetic Cr thin films

Bulk chromium is the simplest antiferromagnet in our general material database, which has been firmly believed to exhibit a collinear spin structure and a consequent vanishing anomalous Hall effect (AHE). In this work, we report an unexpected weak AHE in polycrystalline thin films of chromium. We attribute this phenomenon to the noncollinear spin textures induced by the local spin frustration and rearrangement in certain areas with high residual strain and defect densities. Moreover, a dominant underlying mechanism of intrinsic Berry phase is speculated. This could be a general feature for all the collinear antiferromagnetic thin-film materials with moderately high defect concentrations, making them promising candidates for emergent antiferromagnetic spintronics.

Figure 1

(a) X-ray diffraction pattern, (b) temperature ($T$)-dependent longitudinal resistivity (${\rho }_{xx}$) as well as $\mathrm{d}{\rho }_{xx}/\mathrm{d}T$, and moment versus in-plane and out-of-plane magnetic field at (c) 50 K and (d) 300 K of a Pt(2 nm)/Cr(50 nm)//MgO thin film. The insets show the moment data after subtracting linear backgrounds.

Figure 2

(a) Schematic of the Hall measurement geometry. Magnetic-field-dependent (b) Hall resistance ($R_{xy}$) and (c) anomalous Hall resistance ($R_{xy}^{\mathrm{AH}}$) deduced via subtracting the linear contribution from the ordinary Hall effect in (b) at $T=50–400\mathrm{K}$ of a Pt(2 nm)/Cr(50 nm)//MgO sample.

Figure 3

$R_{xy}^{\mathrm{AH}}$ as a function of the applied field of (a) a Cr(50 nm)//MgO sample and (b) a Cu(2 nm)/Cr(50 nm)//MgO sample. The insets in (a) and (b) illustrate the corresponding film structure.

Figure 4

Deduced ${\rho }_{xy}^{\mathrm{AH}}$ as a function of the applied field of (a) a Pt(2 nm)/Cr(50 nm)//MgO film, (b) a Cr(50 nm)//MgO film, and (c) a Cu(2 nm)/Cr(50 nm)//MgO film. The insets display the corresponding film structure.

Figure 5

(a) ${\rho }_{xx}-T$ curve and (b) ${\rho }_{xy}$ versus magnetic field at different temperatures of a postannealed Pt(2 nm)/Cr(50 nm)//MgO sample.

Figure 6

(a) Magnetic-field dependent ${\rho }_{xy}^{\mathrm{AH}}$ of a Pt(2 nm)/Cr(20 nm)//MgO sample. (b) ${\rho }_{xy}$ versus magnetic field of a Pt(2 nm)/Cr (100 nm)//MgO film. Thickness ($t$)-dependent relative values of (c) ${\rho }_{xy}^{\mathrm{AH}}$ and (d) tangent Hall angle $\left(tan{\theta }_{\mathrm{H}}\right)$ of Pt(2 nm)/$\mathrm{Cr}\left(t\right)$//MgO and (e) ${\rho }_{xx}$ of $\mathrm{Cr}\left(t\right)$//MgO films with respect to those of a platinum-capped and an uncapped 20-nm-thick film, respectively.