Valence fluctuations in Co-doped FeSn antiferromagnetic kagome semimetal

Abstract

Valence fluctuations arising from quantum phenomena in the magnetic kagome lattice offer a unique platform to study the instabilities in charge configuration associated with magnetic interactions. Here, we report the evidence of valence fluctuation in Fe1−yCoySn from x-ray absorption and resonant photoemission measurements. Both the magnetization and magnetoresistance measurements showed an interplay of ferromagnetic and antiferromagnetic interactions, which have temperature and field dependence. An increase in the doping concentration y increases the ferromagnetic interaction in the kagome layer, while the antiferromagnetic interaction in the adjacent kagome layer decreases. We find that the Fe2+ and Co2+ states are associated with ferromagnetic interactions and have localized characters near the Fermi level (EF), while Fe3+ and Co3+ have antiferromagnetic contributions with delocalized characters and lie far away from the EF. A systematic decrease in the density of Fe3+ and Co3+ states over the density of Fe2+ and Co2+ states is observed with increasing y. Thus, the magnetic ordering in Fe1−yCoySn depends on the magnitude of the 2+ and 3+ states of Fe and Co at and near the EF, while the change in spin orientation with an increase in y depends on the changes in spin–orbit coupling and the hybridization between the Fe and Co valence electrons. Hence, Fe1−yCoySn is found to be a valence fluctuating material where the spin state of electrons can be controlled by doping, temperature, and magnetic field, which promises important applications of this material in spintronic, magnetic sensor, and high density data storage devices.