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 electro-magnetic responses including as a large anomalous Hall effect (AHE) and spin Hall conductivity. Here, we report measurements of magneto-transport in c-axis textured Mn3Sn thin films grown on the [111] plane of single crystal MgO. At room temperature, these films display a weak uncompensated magnetic moment of \approx 0.12 \micro_{B}/f.u. in the basal plane and a longitudinal resistivity (\rho_{xx}) close to \approx 3.8 \micro\Omega.m. A residual resistivity ration (\rho_{xx} (300 K)/\rho_{xx} (2 K)) of \approx 3.92 further indicates the high quality of the films. While at 300 K a weak AHE together with field-linear Hall resistivity (\rho_{xy}) is observed in magnetic fields (H) applied perpendicular to the Kagome planes, the temperature (T) dependence of \rho_{xy} shows prominent signatures of three magnetic phases in the temperature regime of 2 to 300 K. The \rho_{xy} also derives a non-trivial topological contribution (\r{ho}THE \approx 1n\Omega.m) in the spin glass phase which appears at T \geq 100 K. Our measurements of anisotropic magnetoresistance (AMR) and planar Hall effect (PHE) over a wide H-T phase space reveal the hitherto unseen effects in the three magnetic phases of Mn3Sn. While the AMR and PHE are negative in the inverse triangular spin phase (250 K \geq T \geq TN), the helical phase (100 \geq T \geq 250 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 \approx 4.4 tesla.

Planar Hall effect and Anisotropic Magnetoresistance in Thin Films of Chiral Antiferromagnet Mn3Sn

Spin-to-charge conversion (S2CC) processes in thin-film heterostructures have attracted much attention in recent years. Here, we describe the S2CC in a 3D topological insulator Bi2Te3 interfaced with an epitaxial film of Fe75Co25. The quantification of spin-to-charge conversion is made with two complementary techniques: ferromagnetic resonance based inverse spin Hall effect (ISHE) at GHz frequencies and femtosecond light-pulse induced emission of terahertz (THz) radiation. The role of spin rectification due to extrinsic effects like anisotropic magnetoresistance (AMR) and planar Hall effects (PHE) is pronounced at the GHz timescale, whereas the THz measurements do not show any detectible signal, which could be attributed to AMR or PHE. This result may be due to (i) homodyne rectification at GHz, which is absent in THz measurements and (ii) laser-induced thermal spin current generation and magnetic dipole radiation in THz measurements, which is completely absent in GHz range. The converted charge current has been analyzed using the spin diffusion model for the ISHE. We note that regardless of the differences in timescales, the spin diffusion length in the two cases is comparable. Our results aid in understanding the role of spin pumping timescales in the generation of ISHE signals.

Lisa Pogue

Papers

Disorder driven variations in magnetoresistance and planar Hall effect in Bi2Te3 thin films