Itinerant ferromagnetism mediated by giant spin polarization of the metallic ligand band in the van der Waals magnet Fe5GeTe2

Abstract

We investigate near-Fermi-energy (EF) element-specific electronic and spin states of ferromagnetic van der Waals (vdW) metal Fe5GeTe2. The soft x-ray angle-resolved photoemission spectroscopy (SX-ARPES) measurement provides spectroscopic evidence of localized Fe 3d band. We also find prominent hybridization between the localized Fe 3d band and the delocalized Ge/Te p bands. This picture is strongly supported from direct observation of the remarkable spin polarization of the ligand p bands near EF, using x-ray magnetic circular dichroism (XMCD) measurements. The strength of XMCD signal from ligand element Te shows the highest value, as far as we recognize, among literature reporting finite XMCD signal for none-magnetic element in any systems. Combining SX-ARPES and elemental selective XMCD measurements, we collectively point an important role of giant spin polarization of the delocalized ligand Te states for realizing itinerant long-range ferromagnetism in Fe5GeTe2. Our finding provides a fundamental elemental selective view-point for understanding mechanism of itinerant ferromagnetism in low dimensional compounds, which also leads insight for designing exotic magnetic states by interfacial band engineering in heterostructures.

Large-scale epitaxy of two-dimensional van der Waals room-temperature ferromagnet Fe5GeTe2

“…The saturation magnetization averaged over in-plane and out-of-plane measurements amounts to Ms = (644 ± 54) kA/m at 10 K, corresponding to a magnetic moment m = (1.95 ± 0.12) µB/Fe. These values are in-line with those previously reported for Fe-deficient Fe5-δGeTe2 (δ = 0.1 -0.3) films exfoliated from bulk crystals 21,33 . Perpendicular to the surface, the saturation field largely increases, indicating an easy-plane magnetic anisotropy.…”

“…We also observed a small polarization of Ge atoms, in agreement with ref. 33 and with our ab initio results (Table 1). As depicted in Figure 4H, both 2p→4d (ΔL=+1) and 2p→4s (ΔL=-1) transitions present a finite XMCD signal.…”

“…In ref. 33 , a sizeable magnetic moment was also observed on Te atoms, but we could not confirm it in our film due to the use of a Te capping layer.…”

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

“…In addition, it can be found that the strongly dispersive bands near the Fermi level also come from Fe 3d orbitals, which contribute to the itinerant moments in the magnetic state. 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 .…”

Tuning the Room Temperature Ferromagnetism in Fe5GeTe2 by Arsenic Substitution

“…[13,14,15,16,17] In general, Fe 5−x GeTe 2 and related Fe 4 GeTe 2 have garnered significant attention recently due to their high ordering temperature and complex behaviors. [18,19,20,21,22,23,24,25,26] The present work was motivated by identifying further routes to tune the magnetism in Fe 5−x GeTe 2 and related bulk phases so that novel properties and logical designs of het-erostructures can be achieved.…”