Planar Hall effect and anisotropic magnetoresistance in thin films of the chiral antiferromagnet Mn3Sn

Antiferromagnetic Weyl semimetals with spin chirality offer excellent platforms to address the Berry phase physics, which manifests prominently in several of their electro-optical and electromagnetic responses including as a large anomalous Hall effect (AHE) and spin Hall conductivity. The ${\mathrm{Mn}}_{3}\mathrm{Sn}$ and ${\mathrm{Mn}}_{3}\mathrm{Ge}$ compounds, where the Mn spins arrange in a kagome lattice, are examples of this class of materials. Here, we report on measurements of magnetotransport in $c$-axis textured ${\mathrm{Mn}}_{3}\mathrm{Sn}$ thin films grown on the [111] plane of single-crystal MgO by dc magnetron sputtering. At room temperature, these films display a weak uncompensated magnetic moment of $\ensuremath{\approx}0.12\phantom{\rule{0.16em}{0ex}}{\ensuremath{\mu}}_{\mathrm{B}}/\mathrm{f}.\mathrm{u}.$ in the basal plane and a longitudinal resistivity (${\ensuremath{\rho}}_{xx}$) $\ensuremath{\approx}3.8\phantom{\rule{0.16em}{0ex}}\ensuremath{\mu}\mathrm{\ensuremath{\Omega}}\mathrm{m}$, which matches well with the bulk value. A residual resistivity ratio $[{\ensuremath{\rho}}_{xx}\phantom{\rule{0.16em}{0ex}}(300K)/{\ensuremath{\rho}}_{xx}\phantom{\rule{0.16em}{0ex}}(2\phantom{\rule{0.16em}{0ex}}K)]$ of $\ensuremath{\approx}3.92$ further indicates the high quality of the films. While at 300 K a weak AHE together with field-linear Hall resistivity (${\ensuremath{\rho}}_{xy}$) is observed in magnetic fields ($H$) applied perpendicular to the kagome planes, the temperature ($T$) dependence of ${\ensuremath{\rho}}_{xy}$ shows prominent signatures of three magnetic phases in the temperature regime of 2--300 K. The ${\ensuremath{\rho}}_{xy}$ also derives a nontrivial topological contribution (${\ensuremath{\rho}}_{\mathrm{THE}}\ensuremath{\sim}1\mathrm{n}\mathrm{\ensuremath{\Omega}}\mathrm{m}$) in the spin-glass phase which appears at $T\ensuremath{\le}100$ K. The origin of the ${\ensuremath{\rho}}_{\mathrm{THE}}$ is attributed to spin textures which may appear in a frustrated chiral spin order. Our measurements of anisotropic magnetoresistance (AMR) and the planar Hall effect (PHE) over a wide $H\ensuremath{-}T$ phase space reveal the hitherto unseen effects in the three magnetic phases of ${\mathrm{Mn}}_{3}\mathrm{Sn}$. While the AMR and PHE are negative in the inverse triangular spin phase ($250\phantom{\rule{0.16em}{0ex}}\mathrm{K}\ensuremath{\le}T\ensuremath{\le}{T}_{\mathrm{N}}$), the helical phase ($100\ensuremath{\le}T\ensuremath{\le}250\phantom{\rule{0.16em}{0ex}}\mathrm{K}$) is devoid of anisotropic in-plane resistivity, and the spin-glass phase shows a sign reversal of AMR with the increasing magnetic field. The origin of this sign change in AMR/PHE is attributed to the emergence of topologically protected spin textures like skyrmions where the fictitious effective magnetic field is estimated to be $\ensuremath{\approx}4.4$ Tesla.