Flat bands and magnetism in $\mathbf{F}{\mathbf{e}}_4\mathbf{GeT}{\mathbf{e}}_2$ and $\mathbf{F}{\mathbf{e}}_5\mathbf{GeT}{\mathbf{e}}_2$ due to bipartite crystal lattices

Abstract

$\mathrm{F}{\mathrm{e}}_{\mathrm{n}=4,5}\mathrm{GeT}{\mathrm{e}}_2$ exhibits quasi-two-dimensional properties as a promising candidate for a near-room-temperature ferromagnet, which has attracted great interest. In this work, we notice that the crystal lattice of $\mathrm{F}{\mathrm{e}}_{\mathrm{n}=4,5}\mathrm{GeT}{\mathrm{e}}_2$ can be approximately regarded as being stacked by three bipartite crystal lattices. By combining the model Hamiltonians of bipartite crystal lattices and first-principles calculations, we investigate the electronic structure and the magnetism of $\mathrm{F}{\mathrm{e}}_{\mathrm{n}=4,5}\mathrm{GeT}{\mathrm{e}}_2$. We conclude that flat bands near the Fermi level originate from the bipartite crystal lattices and that these flat bands are expected to lead to the itinerant ferromagnetism in $\mathrm{F}{\mathrm{e}}_{\mathrm{n}=4,5}\mathrm{GeT}{\mathrm{e}}_2$. Interestingly, we also find that the magnetic moment of the Fe5 atom in $\mathrm{F}{\mathrm{e}}_5\mathrm{GeT}{\mathrm{e}}_2$ is distinct from the other Fe atoms and is sensitive to the Coulomb interaction $U$ and external pressure. These findings may be helpful to understand the exotic magnetic behavior of $\mathrm{F}{\mathrm{e}}_{\mathrm{n}=4,5}\mathrm{GeT}{\mathrm{e}}_2$.

arXiv comment10 pages, 8 figures

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