CoSn is a Pauli paramagnet with relatively flat $d$ bands centered about 100 meV below the Fermi energy, $E_F$. Single crystals of CoSn lightly doped with Fe, In, or Ni are investigated using x-ray and neutron scattering, magnetic susceptibility and magnetization, AC susceptibility, specific heat, and resistivity measurements. Within the rigid-band approximation, hole doping with a few percent of Fe or In should move the flat bands closer to $E_F$, whereas electron doping with Ni should move the flat bands further away from $E_F$. We provide evidence that this indeed occurs. Fe and In doping drive CoSn toward magnetism, while Ni doping suppresses CoSn's already weak magnetic response. The resulting ground state is different for Fe versus In doping. For Fe-doped crystals, ${\mathrm{Co}}_{1-x}{\mathrm{Fe}}_x\mathrm{Sn}$, with $0.02<x<0.27$, the magnetic and specific-heat data are consistent with the formation of a spin glass, with a glass temperature, $T_g$, ranging from 1 K for $x=0.02$ to 10 K for $x=0.27$. Powder and single-crystal neutron diffraction found no evidence of long-range magnetic order below $T_g$ for samples with $x\approx 0.17$. For In-doped crystals, $\mathrm{Co}{\mathrm{Sn}}_{1-y}{\mathrm{In}}_y$, both the magnetic susceptibility and the Sommerfeld coefficient, γ, increase substantially relative to pure CoSn, but with no clear indication of a magnetic transition for $0.05<y<0.2$. CoSn crystals doped with Ni (${\mathrm{Co}}_{0.93}{\mathrm{Ni}}_{0.07}\mathrm{Sn}$) have a significantly smaller magnetic susceptibility and γ than pure CoSn, consistent with flat bands further from $E_F$.

• Received 16 February 2021
• Accepted 1 April 2021

DOI:https://doi.org/10.1103/PhysRevMaterials.5.044202