Electronic Transport Properties Researches Of Three Transition Metal Based Magnetic Alloys

Magnetic skyrmion is a kind of topological protected vortex-like spin structure.With the advantages of the high stability,small size,unique magnetoelectric coupling,skyrmions are considered as the next generation of excellent information carrier.Based on the thinking of the topological Hall effect can be induced by skyrmions,we focus on the potential magnetic materials with topological transport properties trying to obtain the topological Hall effect materials with wide temperature range and low extra critical magnetic field.In this project,the Mn_1.89Pt_0.98Ga_1.12polycrystal,Al substituted Fe₃Ga_4-xAl_xalloys（x=0,0.4,0.6,0.8,1）and YMn₆Sn₆ are systematically studied.The main results are summarized as following:（1）Tetragonal crystalline Mn₂XY with D_2d symmetry is a potential anti-skyrmion material,where anti-skyrmion is found with a wide temperature region and low extra inducing field,indicating a high potential for the practical application.So we prepared Mn_1.89Pt_0.98Ga_1.12 polycrystal,where the spin glass transition were observed at 123 K.The spin glass transition were observed at 123 K.The freezing peaks in AC susceptibility curve and the fitting of the conventional critical slowing down power law,reflect the reentrant character of the spin glass state.Further magnetic property research found that the zero-field cooling exchange bias effects and magnetic memory effects.The topological Hall effect is found in Mn_1.89Pt_0.98Ga_1.12 polycrystals in a large range of temperature（5-220 K）.The value of Topological Hall resistivity increases with decreasing temperature and reaches a maximum of 0.378μΩ?cm at 5 K.The discovery of topological Hall effect show the clue of the topological magnetic structures such as antiskyrmion etc.（2）The existence of the strong topological Hall effect is reported in the"A"phase of Fe₃Ga₄ in the temperature range of 60-390 K.Based on the chemical pressure sensitivity for the magnetic transformation in Fe₃Ga₄,Fe₃Ga_4-xAl_x（x=0,0.4,0.6,0.8,1）series alloys were prepared by the substitution of Al atom with smaller radius than Ga atom.With the replacement of Ga by Al atom,the value of the critical field H₁ inducing the transition from ISDW state to the"A"phase is decreased,while the critical field H₂ for the transition from"A"phase to ferromagnetism wasn’t affected too much.Furthermore,a topological Hall effect was detected with a large range of temperature from60 K to 300 K,with the maximum value of Hall resistivity-0.66μΩ?cm.（3）A giant anomalous Hall effect caused by the topological bands such as Weyl/Dirac fermions ect,and the topological Hall effectas induced by the magnetic structure,were observed in YMn₆Mn₆which can be an idea platform to clarify the mechanism of them.Ti element is used to replace Sn in YMn₆Sn₆ single crystal to modify the exchange interaction between inter-layer Mn atoms,tuning the magnetic structure.It was found that the calculated topological Hall resistivity is dependent on the transverse cone-spiral magnetic structure,which verifies the correlation between topological Hall effect and magnetism.The calculation of anomalous Hall effect mechanism shows that the intrinsic mechanism is still dominant.The anomalous Hall conductivity is calculated to be 55.7Ω^-1cm^-1,which was slightly improved from the original sample.Besides,a large anomalous hall effect contributed by defects was found.