The crystal structure and magnetic properties of GdMn6Ge6−xSix

In the family compounds of RMn6Ge6, GdMn6Ge6 exhibits excellent magnetic properties and a complex magnetic transition behavior. The samples of GdMn6Ge6−xSix were successful prepared by a vacuum arc furnace. The XRD analysis and Rietveld refinement results show that GdMn6Ge6−xSix crystallize in a hexagonal HfFe6Ge6-type structure with space group P6/mmm, and their lattice parameters a and c decrease with the increasing Si content. The M-T curves in the range of 100–600 K indicates that the compounds experienced two magnetic transitions (AFM-FM and FM-PM) and a large thermal hysteresis between ZFC and FCC curves. The AFM-FM transition occurred at Tt for GdMn6Ge6-xSix is a first-order phase transition and the FM-PM transition belongs to a second-order one. The magnetic transition temperature Tt is greatly influenced by the Si content, and the Curie temperature (Tc) for the all samples is roughly the same. The −∆SM for the x = 0, 0.2, 0.4, 0.6 compounds under the applied magnetic field of 1.6 T are 0.83, 1.06, 1.21 and 1.19 J kg−1·K−1 around 486 K, respectively. This relatively large −∆SM of GdMn6Ge6−xSix occurred in a relatively high temperature region and under low applied magnetic field provide a potential material choices in new magnetic refrigeration application.