Anomalous Transverse Transport Responses In A Noncollinear Antiferromagnet Mn₃Sn

Antiferromagnet is a kind of material with the adjacent magnetic moments cancelled each other and the whole exhibits weak magnetism.Mn₃Sn is a non-collinear antiferromagnet with the hexagonal lattice,and also a topological Weyl metal.In this thesis,its rich magnetic and topological properties were studied mainly via several anomalous transverse transport responses.In this study,Mn₃Sn single crystals were grown by two different methods.Firstly,after the millimeter-sized single crystals were obtained by the solid-phase method,three anomalous transverse transport responses of Mn₃Sn were simultaneously detected,namely anomalous Hall effect,anomalous Nernst effect and anomalous Righi-Leduc effect.The behavior of anomalous Hall effect is consistent with that reported in the literature,while the behavior of anomalous Nernst effect and anomalous Righi-Leduc effect is similar to that of anomalous Hall effect,such as consistent hysteresis curves and temperature dependent curves,suggesting the same intrinsic mechanism.Combining anomalous Righi-Leduc effect and anomalous Hall effect,it was found that their ratio conforms to the anomalous transverse Wiedmann-Franz law.Which proved the viewpoint of"intrinsic anomalous Hall effect is a Fermi surface property"proposed by Haldane in 2004.Compared with the results of traditional ferromagnets,the influence of inelastic scattering on anomalous Hall effect in Mn₃Sn was excluded and its origin was pointed to the pure Berry curvature contribution.Secondly,after the centimeter-sized single crystals were obtained by the Bridgman method,the behaviors of the Berry curvature and magnetic domains were studied in Mn₃Sn.With the angle dependent experiments of the anomalous Hall effect,it was found that the total Hall signal was a constant in the single-domain regime when the magnetic field was rotated in xy planes,which proved that the magnetic domains can be rotated freely in xy planes,and the Berry curvature is basically isotropic in the plane.Comparing the curves of the magnetic field dependent anomalous Hall effect and spontaneous magnetization,a topological Hall effect,much larger than that reported in Mn Si,was found in the multi-domain regime of Mn₃Sn.Which provided the indirect evidence for a non-coplanar spin components and real-space Berry curvature in domain walls.Finally,the behaviors of chiral domain walls were studied more deeply in Mn₃Sn.In the direction parallel to the magnetic field,an unexpected planar Hall effect was detected,which was confirmed again by its thermoelectric analogue,the planar Nernst effect.In the direction perpendicular to the magnetic field,a fantastic transverse magnetization signal was detected.By constructing a new chiral domain wall model,the new findings above were successfully explained.And a new domain memory effect with the model was also predicted and confirmed,which is the residual domains locating at the rotated path of the prior field can break the rotated symmetry of magnetic domains,and promote it rotating in a specific direction.Antiferromagnets are hot candidates in spintronics recently,functional devices made of it have the advantages of high speed,low power consumption and small stray field.With the above studies on anomalous transverse transport responses,more studies are expected in Mn₃Sn,such as memory devices,transverse thermoelectric applications,etc.