Abstract
Epitaxial films of the B20-structure compound Fe1-yCoyGe 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.
| Original language | English |
|---|---|
| Article number | 214406 |
| Journal | Physical Review B |
| Volume | 97 |
| Issue number | 21 |
| DOIs | |
| State | Published - Jun 6 2018 |
Funding
We would like to thank C. Morrison for assistance with the patterning of the Hall bars. This work was supported in part by the Science and Technology Facilities Council and the Hitachi Cambridge Laboratory. We are grateful to the ISIS Neutron and Muon Source for the provision of PNR beam time. This research was also supported by the Alexander von Humboldt Foundation, the ERC Synergy Grant SC2 (Grant No. 610115), the Transregional Collaborative Research Center (SFB/TRR) 173 SPIN+X, and Grant Agency of the Czech Republic Grant No. 14-37427G. Y.M. and F.F. acknowledge funding from the German Research Foundation (Deutsche Forschungsgemeinschaft, Grant No. MO 1731/5-1). S.B. and Y.M. acknowledge funding from the European Union's Horizon 2020 research and innovation programme under Grant Agreement No. 665095 (FET-Open project MAGicSky). S.B. and Y.M. also acknowledge support by the Deutsche Forschungsgemeinschaft (DFG) through the Collaborative Research Center SFB 1238. We also gratefully acknowledge J\u00FClich Supercomputing Centre and RWTH Aachen University for providing computational resources. We would like to thank C. Morrison for assistance with the patterning of the Hall bars. This work was supported in part by the Science and Technology Facilities Council and the Hitachi Cambridge Laboratory. We are grateful to the ISIS Neutron and Muon Source for the provision of PNR beam time. This research was also supported by the Alexander von Humboldt Foundation, the ERC Synergy Grant SC2 (Grant No. 610115), the Transregional Collaborative Research Center (SFB/TRR) 173 SPIN+X, and Grant Agency of the Czech Republic Grant No. 14-37427G. Y.M. and F.F. acknowledge funding from the German Research Foundation (Deutsche Forschungsgemeinschaft, Grant No. MO 1731/5-1). S.B. and Y.M. acknowledge funding from the European Union's Horizon 2020 research and innovation programme under Grant Agreement No. 665095 (FET-Open project MAGicSky). S.B. and Y.M. also acknowledge support by the Deutsche Forschungsgemeinschaft (DFG) through the Collaborative Research Center SFB 1238. We also gratefully acknowledge Julich Supercomputing Centre and RWTH Aachen University for providing computational resources.