The magnetic ground states in crystalline systems are significant for both fundamental condensed-matter physics and practical materials engineering. Marcasite ${\mathrm{FeTe}}_2$, characterized as a small-gap semiconductor, exhibits anomalous magnetic behaviors in low-temperature experiments. In this study, first-principles density-functional theory calculations combined with scanning-tunneling microscopy/spectroscopy are employed to investigate the magnetic ground state of marcasite ${\mathrm{FeTe}}_2$. It is revealed that the competition between crystal-field splitting and on-site Coulomb repulsion plays the key role in the formation of localized magnetic moments in ${\mathrm{FeTe}}_2$. The ground state of ${\mathrm{FeTe}}_2$ bulk is confirmed to be nonmagnetic, while the magnetic responses of ${\mathrm{FeTe}}_2$ observed at low temperatures are suggested to be related to the magnetic Fe atoms on the crystal surfaces. Our work proposes a straightforward competing mechanism for determining ground-state magnetism of various localized-moment crystalline systems.

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• Electronic structure
• First-principles calculations
• Magnetism
• Semiconductors
• DFT+U
• Scanning tunneling microscopy