Chemical control of magnetism in the Kagome metal CoSn_1-xIn_x: Magnetic order from nonmagnetic substitutions

The Pauli paramagnet, CoSn consists of Kagome layers of Co, which generates flat bands and a

large density of states near the Fermi energy. When the Fermi energy is positioned within these

bands large electronic instabilities can result. For the Kagome metal, CoSn, this alignment is not

realized and the flat bands are completely filled. We demonstrate that replacing Sn with In

moves the flat bands into the Fermi energy, as expected from simple electron counting. This is

supported by band structure calculations, heat capacity measurements, and angle-resolved

photoemission spectroscopy. The increased density of states results in the emergence of

antiferromagnetic order as evidenced in magnetic susceptibility, Mossbauer spectroscopy and

neutron diffraction data. The Neel temperature reaches a maximum of 32 K for x = 0.4.

Emergence of magnetic order when doping a non-magnetic element, In, into a non-magnetic

Kagome metal is striking. This work provides clear evidence that flat bands from electronically

frustrated lattices in bulk crystals provide a new and powerful way to realize correlated ground

states controlled by crystal chemistry. The effects of hole doping with Fe or Ga will be discussed

as well.