Magnetic And Electrical Transport Properties Of Rare Earth-Transition Metal Compounds RMn₂Ge₂

Rare earth transition metal compounds have received significant attention due to their unique physical properties,including superconductivity,heavy-fermion,and Quantum critical phenomenon.Among them,the RMn2Ge2 compounds have emerged as a research hotspot.Mn in RMn2Ge2 compounds exhibits magnetic ordering at comparatively high temperatures.In addition,some RMn2Ge2 compounds have noncollinear magnetic structures,which lead to anomalous transport behaviors such as the topological Hall effect.Studying the magnetic and electrical transport properties of RMn2Ge2 compounds can deepen our understanding of the interaction mechanisms in materials containing 3d and 4f electrons.Additionally,this research can provide an experimental foundation for magnetic phase transition,anomalous transport,topological configuration,and other related physical phenomena,as well as offer more material choices for applications in magnetic materials,spintronics devices,and other fields.In this thesis,we first introduce the background of rare earth transition metal compounds,magnetic critical analysis,and anomalous Hall effect.Next,we describe the basic principles of crystal growth,characterization,and measurement.Finally,we conduct magnetic and electrical transport studies on SmMn2Ge2,LaMn2Ge2,CeMn2Ge2,and LaxSm1-xMn2Ge2 single crystals.The specific content is as follows.(1)The magnetic properties of SmMn2Ge2 crystal were investigated.Multiple magnetic phase transitions were observed with changing temperature,including a ferromagnetic transition at TC～343 K,a ferromagnetic to antiferromagnetic transition at Tt1～150 K,and a re-entrant ferromagnetic transition at Tt2～100 K.And the easy axis also changed.The critical behavior of the ferromagnetic phase transition was investigated by the modified Arrott plot and Kouvel-Fisher method.The obtained critical exponents and the interaction function were between the theoretical values of long-range and short-range interaction,suggesting the coexistence of multi-range magnetic interactions in SmMnGe2.(2)The electrical transport properties of SmMn2Ge2 single crystal were investigated,revealing an anomalous Hall effect dominated by intrinsic mechanism.And a sign change of Hall resistivity is observed at low temperature.Similarly,LaMn2Ge2 single crystal displays an anomalous Hall effect,with its anomalous Hall conductivity peaking at approximately 0.77 Tc.LaxSm1-xMn2Ge2 single crystals with doping amounts of x=0.53 and 0.87 also exhibit a similar change in the Hall signal as that observed in LaMn2Ge2.(3)The magnetic properties of LaxSm1-xMn2Ge2 single crystals were investigated and magnetic anisotropy was observed.At x=0.30,the transition from the antiferromagnetic state to the ferromagnetic state at low temperature disappeared,and the metamagnetic transition at 125 K no longer existed.However,the transition from the ferromagnetic state to the antiferromagnetic state persisted,and the transition temperature decreases with increasing La doping concentration.Finally,the transition from the ferromagnetic state to the antiferromagnetic state was found to no longer occur in LaMn2Ge2.