Helical magnetic structure and the anomalous and topological Hall effects in epitaxial B20 Fe1−yCoyGe films

Abstract

Epitaxial films of the B20-structure compound Fe 1−y Co y Ge were grown by molecular beam epitaxy on Si (111) substrates. The magnetization varied smoothly from the bulklike values of one Bohr magneton per Fe atom for FeGe to zero for nonmagnetic CoGe. The chiral lattice structure leads to a Dzyaloshinskii-Moriya interaction (DMI), and the films' helical magnetic ground state was confirmed using polarized neutron reflectometry measurements. The pitch of the spin helix, measured by this method, varies with Co content y and diverges at y ∼ 0.45. This indicates a zero crossing of the DMI, which we reproduced in calculations using first-principles methods. We also measured the longitudinal and Hall resistivity of our films as a function of magnetic field, temperature, and Co content y. The Hall resistivity is expected to contain contributions from the ordinary, anomalous, and topological Hall effects. Both the anomalous and topological Hall resistivities show peaks around y ∼ 0.5. Our first-principles calculations show a peak in the topological Hall constant at this value of y, related to the strong spin polarization predicted for intermediate values of y. Our calculations predict half-metallicity for y = 0.6, consistent with the experimentally observed linear magnetoresistance at this composition, and potentially related to the other unusual transport properties for intermediate value of y. While it is possible to reconcile theory with experiment for the various Hall effects for FeGe, the large topological Hall resistivities for y ∼ 0.5 are much larger than expected when the very small emergent fields associated with the divergence in the DMI are taken into account.

Topological Hall effect in thin films of Mn1.5PtSn

“…In contrast to the majority of reports on the THE in conjunction with the AHE, we find that in Mn 1.5 PtSn thin films the size of the THE is of the same magnitude as the corresponding AHE. Typically, the AHE by far surpasses the THE [18,21,24,34]. Nevertheless, similar behavior as in Mn 1.5 PtSn was also presented in the noncollinear metallic Mn 5 Si 3 and the correlated oxide charge-transfer insulator (Ca, Ce)MnO 3 [17,23].…”

Topological and Chiral Spin Hall Effects

“…Such textures appear due to Dzyaloshinskii–Moriya interaction leading to a chiral ordering of magnetic moments. The spin Hall effect driven by electron exchange interaction with chiral spin textures can be detected experimentally via transverse current, the phenomenon known as the topological Hall effect (THE) . It is considered as a perspective tool to probe topologically nontrivial spin structures as well as for device applications such as racetrack memory …”

Weak localization in systems with chiral spin textures and skyrmion crystals

“…The spin-flip scattering rate by a skyrmion coincides with the spin relaxation time of triplet state with projection 1: τ 12 = τ t1 , Eq. (9). In contrast to the coherent subband The magnetic field dependence of the weaklocalization conductivity correction at τ φ /τ0 = 30 for (a) different spin texture radius kF a (at α = π/2) and (b) different spin inclination angle α (at kF a = 3).…”

“…The ongoing decade has been featured by an impressive rise of chiral magnetism. Various chiral spin textures, such as magnetic skyrmions [1][2][3][4][5] and antiskyrmions [6,7], skyrmion lattices [8,9], merons and bimerons [10][11][12] are being extensively studied both experimentally and theoretically. The interest is especially heated by the fact that the chiral nature of such textures opens up a novel physics with a number of intriguing phenomena, such as the topological Hall effect [13][14][15][16][17], its reciprocal analog -the skyrmion Hall effect [18,19], the anomalous Nernst effect [20] or nontrivial magnonskyrmion interaction [21].…”