Magnetic Properties And Anomalous Hall Effect Of Single Crystal CoNb₃S₆

Although the phenomena of Anomalous Hall Effect has been discovered for more than one hundred of years,the intrinsic mechanism of the Anomalous Hall Effect is still unclear.In addition,the Anomalous Hall Effect is usually not expected in a collinear antiferromagnet,when the net magnetization is zero.However,recently,it has been shown that the Anomalous Hall Effect can exist in non-collinear antiferromagnetic materials due to the Berry phase curvature in momentum space caused by the special spin configuration.In this dissertation,we will focus on the Anomalous Hall Effect observed in the antiferromagnetic intercalated transition metal dichalcogenide CoNb₃S₆,where the conventional argument of the anomalous Hall effect in ferromagnet does not apply.Single crystals of intercalated transition metal dichalcogenide CoNb₃S₆ were synthesized by the chemical vapor transform method.Single crystal X-Ray diffraction has been performed at room temperature,and all the grown crystals of CoNb₃S₆ was refined to be of the same structure with the chiral space group P6322?No.182?,and the ratio of different elements was verified to be Co:Nb:S?1:3:6.However,with lowering temperature,it was found that different crystals even grown from the same batch behave differently.Magnetic susceptibility,specific heat and transport measurements indicate distinct magnetic properties on different samples although they all show the same crystal structure at room temperature.We have select four representative samples,and all the thermal and related transport properties were presented.The Anomalous Hall Effect has been observed in two of the four samples,while it is absent in the other two samples.These observations have not been reported in the previous reports.Based on these detailed study,we found out that the Anomalous Hall Effect are related to the existence of the canted ferromagnetic components in CoNb₃S₆ samples,but on the other side,the weak ferromagnetic components can not explain such a giant Anomalous Hall Effect coefficient.Although the neutron scattering experiments suggested that the antiferromagnetic order is collinear,we still can not rule out the possibility that the non-collinear antiferromagnetic order persist in some of the samples with large Anomalous Hall Effect.Further study with single crystal neutron diffraction on different samples are needed to clarify the origin of the Anomalous Hall Effect in CoNb₃S₆.