Relating spin-polarized STM imaging and inelastic neutron scattering in the van der Waals ferromagnetFe3GeTe2

Abstract

Van der Waals (vdW) ferromagnets have enabled the development of heterostructures assembled from exfoliated monolayers with spintronics functionalities, making it important to understand and ultimately tune their magnetic properties at the microscopic level. Information about the magnetic properties of these systems comes, so far, largely from macroscopic techniques, with little being known about the microscopic magnetic properties. Here, we combine spin-polarized scanning tunneling microscopy and quasiparticle interference imaging with neutron scattering to establish the magnetic and electronic properties of the metallic vdW ferromagnet Fe 3 GeTe 2 . By imaging domain walls at the atomic scale, we can relate the domain wall width to the exchange interaction and magnetic anisotropy extracted from the magnon dispersion as measured in inelastic neutron scattering, with excellent agreement between the two techniques. From comparison with density functional theory calculations we can assign the quasiparticle interference to be dominated by spin-majority bands. We find a dimensional dichotomy of the bands at the Fermi energy: bands of minority character are predominantly two-dimensional in character, whereas the bands of majority character are three-dimensional. We expect that this will enable new design principles for spintronics devices.

Spin stiffness and spin excitation gap of van der Waals ferromagnetic Fe 3 + δ

“…The measured samples have small spin wave gaps, consistent with theoretical predictions [52]. The ∆ values obtained in this work are lower than a 3.7 meV spin excitation gap from inelastic neutron scattering (INS) measurement from [39], higher than a zero spin excitation gap from the INS measurement from [16] and close to the results from the INS measurement in [38]. Cr-based vdW ferromagnets have higher ∆ values, 0.59 ± 0.34 meV (CrI 3 ), 0.37 ± 0.22 meV (CrSiTe 3 ), 0.28 ± 0.19 meV (CGT), and 0.45 ± 0.33 meV (Cr 1.21 Te 2 ) [51].…”

“…As a ferromagnetic metal, FGT has both itinerant and local magnetic moment components [16,38,39]. The degree of itinerancy of the magnetic electrons can be evaluated by the RWR, P c /P s , proposed in 1963 [53,54].…”

“…Bulk magnetization measurements on FGT have shown the existence of itinerant magnetism using the Rhodes-Wohlfarth ratio (RWR) and generalized RWR [15,17]. Inelastic neutron scattering measurements provided direct spectroscopic evidence on the coexistence of localized magnetic moments and itinerant magnetism from free electrons [16,38,39]. The observed spin wave dispersion shows local momentslike features at the zone center and a column-like broad continuum from itinerant electrons at the zone boundary [16].…”

“…Extensive research efforts have been dedicated to elucidating the mechanisms underlying magnetism in FGT. These efforts encompass a wide array of investigations, including dc and ac magnetic measurements [15,40], studies on magnetocrystalline anisotropy [24, 30], electronic band structure characterization [24,41], analyses of spin wave dispersion relationships [16,38,39], topological spiral spin configurations [32], interlayer coupling [42], and Monte Carlo simulations using various models [43]. However, systematic analysis of low-temperature magnetism as a function of Fe concentration is lacking.…”

Proposal for All-Electrical Skyrmion Detection in van der Waals Tunnel Junctions

“…To go beyond the nanoscale skyrmion (Figure b) and to vary the period of the noncollinear spin structure on a larger scale, we locally approximate the electronic structure in a skyrmion by that of a homogeneous spin spiral state . This approach can explain the experimentally observed NCMR effect of skyrmions and domain walls in ultrathin films. , Note that spin-polarized STM was used to resolve domain walls in FGT. , …”