Electron Counts, Structural Stability, and Magnetism in BaCuSn$_2$-CeNi$_1$$_-$$_x$Si$_2$-type YT$_x$Ge$_2$ (T= Cr, Mn, Fe, Co, and Ni)

TL;DR

This study explores the structural stability, electron count relationships, and magnetic properties of YT$_x$Ge$_2$ compounds with T= Cr, Mn, Fe, Co, Ni, revealing how transition metal incorporation affects magnetism and suppresses superconductivity.

Contribution

It provides new insights into how electron counts and transition metal site occupancies influence structural stability and magnetic behavior in YT$_x$Ge$_2$ compounds.

Findings

Smaller transition metals have higher site occupancies.

Stable configurations occur at approximately 10.3 electrons per transition metal.

Mn-based compound exhibits ferromagnetism at 293 K.

Abstract

Results of crystallographic refinement, the relationship between electron counts and structural stability, and magnetic characterization of YT$_x$Ge$_2$ (T= Cr, Mn, Fe, Co, and Ni) prepared using the arc melting method are presented. These YT$_x$Ge$_2$ compounds crystallize in the BaCuSn$_2$-CeNi$_1$$_-$$_x$Si$_2$-type structure with space group Cmcm, and the site occupancies of 3d transition metals range from x = 0.22(1) for Cr to x = 0.66(1) for Ni. Based on a combination of single crystal and powder X-ray diffraction and scanning electron microscopy, the trends are clearly established that the smaller transition metal atoms exhibit larger occupancies on T (Cu) site. Our investigation into the relationship between electron count and site defect reveals that a stable configuration is obtained when reaching 10.3e- per transition metal (Y+T), which strongly correlates with the defect observed in the case of T metals. Magnetic properties measurements indicate paramagnetism for T = Cr, Fe, and Co, but ferromagnetism for T = Mn with a Curie temperature at 293 K and effective moment ~ 3.6 uB/Mn. The absence of superconductivity in this series is surprising because they consist of similar building blocks and electron counts to superconducting YGe$_1$$_.$$_5$$_+$$_d$Si$_2$ 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.