Structure,Magnetism And Magnetocaloric Effects Of Honeycomb-lattice Compounds GdXTeO₆(C=Cr,Mn)

In recent years,due to the potential application of magnetic refrigeration technology,the exploration of new magnetic materials with large magnetic entropy change has attracted much attention.In this paper,we synthesized the honeycomb lattice compounds GdCrTeO₆ and GdMnTeO₆,and studied their crystal structure,magnetism and magnetocaloric effects.The main contents are as follows:1.The research background,basic principle of magnetic refrigeration,magnetocaloric effects,sample preparation methods,crystal structures and magnetic characterization equipments are briefly summarized.2.Polycrystalline samples of GdCrTeO₆ and GdMnTeO₆ were synthesized by solid phase method.X-ray powder diffraction results show that the samples are single phase with layered honeycomb crystal structure,and the space groups are P-3 and P-31C,respectively.The structure parameters of GdCrTeO₆ and GdMnTeO₆ are obtained by Retiveld refinement.3.The susceptibility curves of GdCrTeO₆ exhibit paramagnetic behavior,but the Curie-Weiss temperature is-7.32 K which indicates that the antiferromagnetic(AFM)interaction is dominant.A?-like peak appears at?10 K in the zero-field specific heat curve,which proves the existence of AFM ordering.We believe that the magnetism of Gd³⁺and Cr³⁺ions is independent of each other,and the AFM ordering originates from the AFM interaction between Cr³⁺ions,while the Gd³⁺ions are paramagnetic,which is further confirmed by the electron spin resonance experiment.4.The susceptibility curves of GdMnTeO₆ have a peak at?7.7 K,which corresponds to the paramagnetic-AFM phase transition.The Curie-Weiss temperature is2.6 K,which is close to zero and indicates that the AFM and ferromagnetic interactions are comparable in magnitude.The low temperature magnetization curves present a magnetic-field-induced AFM to ferromagnetic phase transition at the critical magnetic field 0.7 T.The electron spin resonance experiment further confirms the occurrence of magnetic-induced phase transition.5.The study of magnetocaloric effect shows that the maximum magnetic entropy change of GdCrTeO₆ and GdMnTeO₆ is 41.8 J×kg^-1×K^-1and 29.8 J×kg^-1×K^-1,respectively,for a magnetic field change of 0-7 T.Particularly,the maximum magnetic entropy change of GdCrTeO₆ in the low field(3 T)can reach 31.3 J×kg^-1×K^-1.These values exceed those of the most Gd-based magnetic refrigeration materials.Considering that the two compounds have no magnetic/thermal hysteresis,they can be used as candidate materials for magnetic refrigeration in low temperature region.