Preparation And Physical Properties Of Non-colinear Antiferromagnetic Mn₃Sn Thin Film

The internal atomic magnetic moments of noncollinear antiferromagnetic materials are arranged in noncollinear geometric relationships.As a result of this unique magnetic structure,there are unique physical phenomenon in nonlinear antiferromagnetic materials that cannot be observed in common antiferromagnetic materials.For instance,in a recent study,researchers reported the discovery of a remarkable anomalous Hall effect in non-collinear antiferromagnetic Mn₃Sn single crystal.However,as for the research on Mn₃Sn.thin film samples,only a few works have obtained polycrystalline films with random orientation or heteroepitaxial films with discrete island shapes.The possible reasons for the discretization of heteroepitaxial films may include the segregation tendency of the Mn₃Sn itself or the large lattice mismatch between the film and the substrate.In this thesis,we explored the preparation process of continuous heteroepitaxial Mn₃Sn thin film and the factors that affect the anomalous Hall effect in thin films.The research results provide important information for further understanding the cause of the anomalous Hall effect phenomenon in non-collinear antiferromagnetic materials.The main contents of this thesis are as follows:1.Mn₃Sn thin films were prepared by stepwise selection of three single crystal substrates Ru-YSZ,MgO and LiF with smaller mismatches by magnetron sputtering.By changing the thickness of the Ru buffer layer,it was proved that the Mn₃Sn island-like morphology during the heteroepitaxial growth in the related literature reports is mainly related to the surface energy between the substrate and the film,not the quality of the buffer layer.The transmission electron microscope was used to investigate the element distribution and cross-section morphology of the epitaxial continuous Mn₃Sn thin film.It was found that the obtained continuous thin film sample was composed of Mn₃Sn crystal with good epitaxiality and a small amount of amorphous.The segregation of Sn in the sample is the main factor determining the morphology of the sample surface.Finally,a(0001)plane Mn₃Sn thin film with good orientation and continuity was successfully prepared on Li F single crystal substrate,and the optimal process parameters under the existing experimental conditions were obtained.2.The magnetic response and electrical transport performance of the epitaxial continuous Mn₃Sn film were measured by superconducting quantum interference device and comprehensive physical property measurement system.The results showed that,compared with the bulk Mn₃Sn single crystal,the Mn₃Sn film has an unbalanced net magnetic moment vertical to the film surface due to the introduction of lattice defects,etc.This phenomenon leads to the presence of the anomalous Hall effect when a magnetic field is applied in the direction perpendicular to the sample surface.As the thickness of the sample increases,the crystallinity of the thin film sample is improved.At the same time,the anomalous Hall effect in the direction mentioned above is gradually weakened,as the step-jump value of the lateral Hall resistance under the magnetic field gradually decreases with increasing thickness.