Research Of Magnetic And Electric Properties And Anomalous Hall Effect Of Mn-Based Antiferromagnetic Compounds

The anomalous Hall effect is an important physical phenomenon in spintronics.For a long time,traditional antiferromagnetic materials have been considered to not exhibit anomalous Hall effects due to the cancellation of positive and negative spins.However,after continuous exploration,it has been found that there is a huge anomalous Hall effect in Mn based nonlinear antiferromagnetic materials.At the same time,because of their unique spin structure,these antiferromagnetic materials have faster response speed and are less vulnerable to magnetic field interference than ferromagnetic materials,which opens the way for the design and preparation of new spin electronic devices.This article uses arc melting technology and subsequent heat treatment to prepare Mn based antiferromagnetic materials,such as Mn₇₇Ge₂₃,Mn₇₂Ga₂₈,Mn₃Ga_1-xGe_x（x=0.2,0.5,0.8）,Mn_1.5V_0.5FeGa.The phase structure,magnetoelectric properties,Hall effect,and their interrelationships of Mn based antiferromagnetic materials were studied.This study further enhances the potential of this type of material in the field of spin electronic devices.By and large,the main research contents and conclusions have been shown as follow:1.The samples of Mn₇₇Ge₂₃ and Mn₇₂Ga₂₈ samples were prepared by high temperature arc melting technology.They are hexagonal system with P₆₃/mmc space group.The investigation of their magnetic and electric properties as well as Hall effect have provided that both Mn₇₇Ge₂₃ and Mn₇₂Ga₂₈ samples have triangular antiferromagnetic spin structures,and encounter lattice geometry distortion at 360K～380 K and 170 K～240 K respectively.In addition,both samples have large anomalous Hall resistivity,and the internal mechanism of anomalous Hall effect is intrinsic KL mechanism or side-jump mechanism.At room temperature,the anomalous Hall resistivity of Mn₇₇Ge₂₃ and Mn₇₂Ga₂₈ samples reaches 0.41μΩcm and 0.28μΩcm respectively.For Mn₇₂Ga₂₈sample,the topological Hall effect was extracted through fitting,and it was found that the topological Hall effect was present below 300K,and the topological Hall resistivity reached the maximum value of 0.441μΩcm at50 K.2.Polycrystalline Mn₃Ga_1-xGe_x（x=0.2,0.5,0.8）alloy was obtained from high purity Mn,Ga and Ge elements by means of arc melting technology and subsequent heat treatment.The effects of Ge with various concentration doping on the structure,magnetic and electric properties and Hall effect of samples was analyzed.The results show that Mn₃Ga_1-xGe_x（x=0.2,0.5,0.8）alloys are all hexagonal and the space group is P₆₃/mmc.With increasing doping concentration of Ge element,the Neel temperature of those samples decrease gradually,and the Neel temperature of Mn₃Ga_1-xGe_x（x=0.2,0.5,0.8）is 465 K,437 K,400 K respectively.Meanwhile,the doping concentration of Ge element also has bearing on the magnetic range of the sample.As a small amount doping of Ge element（x=0.2）causes part of the spin orientation to move out of plane ab at low temperature,the magnetic properties of Mn₃Ga_0.8Ge_0.2sample show a steep upward trend at 200 K.However,the spin tilt is not easy to occur when the Ge element is doped with appropriate amount and excessive amount（x=0.5,0.8）.Thus the magnetic properties in the samples of Mn₃Ga_0.5Ge_0.5 and Mn₃Ga_0.5Ge_0.8 show an overall gentle upward tendency.The magnetic increase of Mn₃Ga_0.2Ge_0.8 at around 75 K is mainly due to the presence ofα-Mn.Additionally,Mn₃Ga_0.8Ge_0.2 sample showed a higher magnetoresistance（38.5%）at 200 K.The Hall effect measurement of Mn₃Ga_1-xGe_x（x=0.2,0.5,0.8）shows that the anomalous Hall resistivity increases with the increasing doping concentration of Ge element,and the Hall effect is still the intrinsic KL mechanism or side-jump mechanism.At room temperature,the anomalous Hall resistivity of Mn₃Ga_0.8Ge_0.2,Mn₃Ga_0.5Ge_0.5 and Mn₃Ga_0.2Ge_0.8 are 0.70μΩcm,0.79μΩcm and 0.84μΩcm respectively.The topological Hall effect is observed when the temperature of Mn₃Ga_0.8Ge_0.2 is lower than200 K,and the topological Hall resistivity of Mn₃Ga_0.8Ge_0.2reaches the maximum value of 0.242μΩcm at 120 K.3.The Mn_1.5V_0.5FeGa alloy was prepared through arc melting technology,and its phase structure,magnetic and electric properties,and Hall effect were investigated.Mn_1.5V_0.5FeGa is a cubic structure with a space group of Fm-3m.Through Hall measurements,the result shows that the anomalous Hall resistivity of Mn_1.5V_0.5FeGa alloy is relatively high and reaches 1.79μΩcm at room temperature,which is 1.51μΩcm higher than that of Mn₃Ga at high temperatureεphase.