Anomalous transport in itinerant van der Waals ferromagnets Fe$_n$GeTe$_2$ (\emph{n}=3, 4, 5)

Abstract

Ferromagnetic (FM) semimetals FenGeTe2(n=3, 4, 5), exhibit several symmetry-protected bandcrossing points or lines near the Fermi energy (EF ) and these topological properties of energy bands lead to interesting transport properties. We study these materials employing the first-principle calculations and the tight-binding Hamiltonian constructed by fitting the parameters of the first principles calculation. In the presence of spin-orbit coupling (SOC) for n=3,5 a large Berry curvature (BC) concentrated on the nodal lines is observed. The consequence of the correlation of the topological nodal line and magnetic moments on anomalous Hall conductivity (AHC) σxy and anomalous Nernst conductivity (ANC) αxy have been investigated. We find σxy = 150 S/cm for n=3, 295 S/cm for n=4, and 90 S/cm for n=5 at 0 K, while the ANC is observed as αxy = 0.55 A/Km for n=3, 0.10 A/Km for n=5, and 0.80 A/Km for n=4, at the EF at room temperature. Our calculated AHC values at 0 K, i.e., 150 S/cm for Fe3GeTe2 and 90 S/cm Fe5GeTe2, are consistent with the experimentally reported values. Also the experimentally reported value of ANC for Fe5GeTe2 is close to our calculated value at room temperature, i.e., 0.10 A/Km.

Spin-reorientation driven emergent phases and unconventional magnetotransport in quasi-2D vdW ferromagnet Fe4GeTe2

“…The low-temperature value is almost three times smaller than the expected AHE conductivity in the 'resonant' condition, ∼ e 2 /ha ≈ 390 Ω −1 cm −1 [14,73] in three dimensions, where e is the electronic charge, h is the Planck constant and a = 9.97 Å [20], being the lattice constant of F4GT. Also, the recent DFTbased calculations show that F4GT belongs to a different magnetic symmetry class compared to the other two members, having a non-trivial Berry curvature leading to the the low-temperature AHE conductivity via intrinsic K-L mechanism [46]. However, the strong temperature dependence of the AHE suggests that extrinsic mechanisms might play a role in determining the AHE in F4GT.…”

“…The stacking of these F4GT monolayers forms a rhombohedral structure with space group R 3m [20]. Electronically this has been predicted to be a different class with nontrivial topology, unlike F3GT or F5GT [46,47]. Single crystal of F4GT was prepared by the chemical vapor transport (CVT) methods exhibiting the ferromagnetic T C ∼ 270 K where the dM/dT reaches its minimum, followed by the SRT at ∼ 120 K below which the magnetization along out-of-plane direction becomes larger than that of its in-plane value (Fig.…”

“…Besides the unusual magnetic properties, electronically these materials possess interesting features. All the members of the FnGT family are predicted to be semimetal as the DFT-based calculations show multiple band crossing at the Fermi level [46,47]. More importantly, the presence of different crystal symmetry and the spin-orbit coupling (SOC) may suggest a topologically nontrivial phase with unusual effects induced by the chiral anomaly like negative magnetoresistance or nonlinear conductivity in the diffusive limit [14].…”