Scattering mechanisms in textured FeGe thin films: Magnetoresistance and the anomalous Hall effect

Abstract

A textured thin film of FeGe was grown by magnetron sputtering with a helimagnetic ordering temperature of TN = 276 ± 2 K. From 5 K to room temperature a variety of scattering processes contribute towards the overall longitudinal and Hall resistivities. These were studied by combining magnetometry and magnetotransport measurements. The high-field magnetoresistance (MR) displays three clear temperature regimes: Lorentz force MR dominates at low temperatures, above T ≈ 80 K scattering from spin-waves predominates, whilst finally for T 200 K scattering from fluctuating local moments describes the MR. At low fields, where the magnetisation is no longer technically saturated, we find a scaling of magnetoresistance with the square of the magnetisation, indicating that the MR due to the unwinding of spins in the conical phase arises from a similar mechanism to that in magnetic domain walls. This MR is only visible up to a temperature of about 200 K. No features can be found in the temperature or field dependence of the longitudinal resistivity that belie the presence of the underlying magnetic phase transition at TN: the marked changes in behavior are at much lower temperatures. The anomalous Hall effect has a dramatic temperature dependence in which the anomalous Hall resistivity scales quadratically with the longitudinal resistivity: comparison with anomalous Hall scaling theory shows that our system is in the intrinsic "moderately dirty" regime. Lastly, we find evidence of a topological Hall effect of size ∼ 100 µΩcm.

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

“…There have also been studies on thin films of FeGe, which show skyrmions close to room temperature with a helix pitch of 70 nm [30] that can be driven at low current density [31]. Topological Hall effects have been observed in a variety of different FeGe films [32][33][34], which can be discretized in small geometries comparable to the skyrmion size [35]. FeGe shows an AHE that is due primarily to the intrinsic mechanism [33].…”

“…Topological Hall effects have been observed in a variety of different FeGe films [32][33][34], which can be discretized in small geometries comparable to the skyrmion size [35]. FeGe shows an AHE that is due primarily to the intrinsic mechanism [33]. An enhanced ordering temperature has been seen in FeGe films grown on MgO [36].…”

Chiral magnetic excitations in FeGe films

“…Furthermore, recent Lorentz transmission electron microscopy and transport studies of FeGe and MnSi thin films have brought into question the common interpretation of the topological Hall effect as arising solely from a skyrmion lattice phase [13,19,24,25]. These studies point out that transport measurements of B20 films are hard to interpret unambiguously because electron skew scattering by complex helical spin structures also contributes a Hall effect signal [13,26]. These difficulties motivate the application of alternative characterization methods to help identify chiral magnetic states and quantify magnetic behavior in thin film materials.…”

Topological spin dynamics in cubic FeGe near room temperature

“…This specificity gives MAS an advantage as compared to electrical measurements such as the topological Hall effect, [17][18][19][20][21][22] which is more difficult to interpret because the signals are not unique to skyrmion phases or helical phases. [19][20][21][22][23][24] In this letter, we present a study of spin-wave dynamics in a single crystal of B20 FeGe using MAS. Specifically, we measure the gigahertz frequency dynamic susceptibility of FeGe using a field-referenced lock-in technique, which significantly increases our sensitivity to magnetic phase boundaries as compared to conventional MAS.…”

“…FeGe also has the closest lattice match to Si [111] substrate and it can be grown by magnetron sputtering for a scalable fabrication of relevant applications. 22,24,26 While FeGe has been the object of great interest in recent imaging, transport, and neutron scattering experiments, 9,10,25,27,28 the spin dynamics of its many magnetic phases are relatively unexplored.The single crystal of B20 FeGe was grown by chemical vapor transport as described by Richardson. 29 We determined the structure and crystallographic orientation of a millimetersized, pyramid-shaped B20 FeGe crystal using Laue X-ray diffraction prior to MAS experiments (see Fig.…”