Electron counts, structural stability, and magnetism in BaCuSn₂-CeNi_1-xSi₂-type YT_xGe₂ (T= Cr, Mn, Fe, Co, and Ni)

Results of crystallographic refinement, the relationship between electron counts and structural stability, and magnetic characterization of YT_xGe₂ (T = Cr, Mn, Fe, Co, and Ni) prepared using the arc melting method are presented. These YT_xGe₂ compounds crystallize in the BaCuSn₂-CeNi_1-xSi₂-type structure with space group Cmcm, and the site occupancies of 3d transition metals range from x = 0.22 (1) for Cr to x = 0.66 (1) for Ni. Based on a combination of single crystal and powder X-ray diffraction and scanning electron microscopy, the trends are clearly established that the smaller transition metal atoms exhibit larger occupancies on T (Cu) site. Our investigation into the relationship between electron count and site defect reveals that a stable configuration is obtained when reaching 10.3e- per transition metal (Y + T), which strongly correlates with the defect observed in the case of T metals. Magnetic properties measurements indicate paramagnetism for T = Cr, Fe, and Co, but ferromagnetism for T = Mn with a Curie temperature of ∼293 K and effective moment ∼3.6 μ_B/Mn. The absence of superconductivity in this series is surprising because they consist of similar building blocks and electron counts to superconducting YGe_1.5+δ except for 3d transition metals. Introducing 3d transition metals into the system plays a critical role in suppressing superconductivity, offering new insights into the interplay between superconductivity and magnetism in layered intermetallics.