Study On Magnetism And Magnetic Phase Transition Of Rare Earth Triangular-lattice Compounds

Triangular lattice rare earth compounds are prone to geometric frustration due to their special lattice structure.Because geometric frustration will lead to rich physical properties in materials,the study of such materials is of great significance for solving many basic problems in the field of condensed matter physics.In addition,the magnetic moment of rare earth atoms is large,and it may have better magnetic refrigeration performance.In this study,single crystals of α-DyGa3 and NdAuAl4Ge2 with triangular lattices were successfully grown by the self-flux method.The structures of the single crystals were characterized by means of X-ray Diffractometer(XRD).The composition of single crystals was determined by Energy Dispersive Spectrometer(EDS)spectroscopy in a scanning electron microscope(SEM,XL30,PHILIPS).The properties of magnetism and magnetic phase transition were characterized using a Superconducting Quantum Interference Device magnetomete(SQUID),and its electrical transport properties and specific heat properties were measured and calculated using a Physics Properties Measurement System(PPMS).The neutron powder diffraction(NPD)determined the magnetic structure of the compound.The main conclusions are as follows:We successfully grown α-DyGa3 single crystals by self-flux method.The antiferromagnetic ordering temperature of α-DyGa3 is 7.2 K,and the Curie-Weiss temperatures of the ab-plane and c-axis directions are-27.7(1)K and-31.3(1)K,respectively.The frustration parameter is about 4.The experimental result of the neutron powder diffraction shows that α-DyGa3 is a collinear antiferromagnet with the magnetic propagation vector k=(1/2,0,1/2)and the magnetic space group Cc2/c(BNS#15.90,origin at(0,0,0)).The magnetic moment of α-DyGa3 is located in the ab-plane and perpendicular to the b-axis,with an alternating stripe antiferromagnetic structure in the ab-plane.At 3.5 K,the magnetic moment is 5.72(12)μB per Dy3+.Single crystals of NdAuAl4Ge2 compounds were grown using Al-Ge as the flux,and the magnetic phase transitions were studied by measuring isothermal magnetization curves and specific heat curves under different magnetic fields.Finally,lowtemperature magnetic phase diagrams were obtained.The results show that the antiferromagnetic ordering temperature of NdAuAl4Ge2 is TN=1.74 K.As the magnetic field increases,the ordering temperature decreases.The Curie-Weiss temperatures of the c-axis and ab-plane are about-40 K and-30 K,respectively,and the frustration parameters are about 23,indicating that NdAuAl4Ge2 is a good geometrical frustration material.When a magnetic field is applied along c-axis at temperatures below 1.4 K,there are multiple field-induced magnetic transitions.The magnetization curve at 0.06 K has magnetization plateaus at approximately Ms/3 and Ms/2 for a magnetic field H parallel to the c-axis.