Kondo Holes in the Two-Dimensional Itinerant Ising Ferromagnet Fe₃GeTe₂

Abstract

Heavy Fermion (HF) states emerge in correlated quantum materials due to the intriguing interplay between localized magnetic moments and itinerant electrons but rarely appear in 3d-electron systems due to high itinerancy of d-electrons. Here, an anomalous enhancement of Kondo screening is observed at the Kondo hole of local Fe vacancies in Fe3GeTe2 which is a recently discovered 3d-HF system featuring Kondo lattice and two-dimensional itinerant ferromagnetism. An itinerant Kondo–Ising model is established to reproduce the experimental results and provides insight into the competition between Ising ferromagnetism and Kondo screening. Our work explains the microscopic origin of the d-electron HF states in Fe3GeTe2 and inspires future studies of the enriched quantum many-body effects with Kondo holes.

Neutron spectroscopy evidence on the dual nature of magnetic excitations in a van der Waals metallic ferromagnet Fe$_{2.72}$GeTe$_{2}$

“…Furthermore, the orbital-resolved band structures also reveal that the localized orbitals have distinct hybridizations with some strongly dispersive bands near the Fermi level, which can induce the formation of the Kondo singlets between the local moments and itinerant electrons 58,91 . We consider our results reflect the dual properties of the 3d electrons 58,59,61 , which has been reported for Fe in ironbased superconductors 92 .…”

“…According to these results, we consider that the combination of itinerant and local-moment pictures is essential to explain the nature of magnetism in this material 58,59,61 . The final question is what is the microscopic origin of the local and itinerant moments in Fe 2.72 GeTe 2 ?…”

“…It is worth mentioning that the spin frustration for the itinerant electrons can be relieved in the vicinity of a Kondo hole. This in turn will enhance the Kondo screening effect on the local moments adjacent to the Kondo hole 59 , and reduce the ferromagnetic interactions between the local spins. We believe that the T C is primarily controlled by the exchange coupling between the local spins 73,74 , considering the huge splitting energy ∆ of ∼1.5 eV which is about two orders of magnitude higher than the T C .…”

“…The T C of Fe 3−x GeTe 2 usually ranges from 140 to 230 K, depending on the stoichiometric amount of Fe atom [44][45][46][47][48][49][50][51][52][53] . It exhibits abundant fascinating physical properties, such as large anomalous Hall effect induced by topological nodal lines 52,[54][55][56] , topological spin texture 57 , Kondo-lattice physics 58,59 , and large effective electron mass renormalization and electronic correlations 60,61 . More intriguingly, the realization of a stable and tunable two-dimensional (2D) ferromagnetism even down to monolayer makes it a great platform for developing new spintronic devices based on magnetic vdW heterostructures 50,[62][63][64][65][66][67] .…”

Pervasive beyond room-temperature ferromagnetism in a doped van der Waals magnet: Ni doped Fe$_5$GeTe$_2$ with $T_{\text{C}}$ up to 478 K

“…In Ni-F5GT, the electrons provided by the Ni dopants may greatly influence the electronic band structure and the density of states (DOS) near the Fermi level (E F ). Alternatively, the magnetic exchange coupling J i,j between spins S i and S j on sites i and j, might also be altered via the Ruderman-Kittel-Kasuya-Yosida (RKKY) exchange since the electronic structure is likely altered substantially by Nidoping [25,28,50,51]. All together, the itinerant FM might also be enhanced by electron doping in Ni-F5GT.…”