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Magnetic Field-Induced Non-Trivial Electronic Topology in Fe3−xGeTe2



Juan Macy, Danilo Ratkovski, Purnima P. Balakrishnan, Mara Strungaru, Yu-Che Chiu, Aikaterini Flessa, Alex Moon, Wenkai Zheng, Ashley Weiland, Gregory T. McCandless, Julia Y. Chan, Govind S. Kumar, Michael Shatruk, Alexander Grutter, Julie Borchers, William D. Ratcliff, Eun S. Choi, Elton J. Santos, Luis Balicas


The anomalous Hall, Nernst and thermal Hall coefficients of the itinerant ferromagnet Fe3−xGeTe2 display several features upon cooling, like a reversal in the Nernst signal below T = 50 K pointing to a topological transition possibly associated to the development of bulk magnetic spin textures. Since the anomalous transport variables are directly related to the texture of the Berry curvature, a possible topological transition might imply deviations from the Wiedemann-Franz (WF) law. This law has not yet been validated for the anomalous transport variables given that recent experimental studies yield contradictory, material-dependent results. Despite these features, the anomalous Hall and thermal Hall coefficients of Fe3−xGeTe2 are found, within our experimental accuracy, to satisfy the WF law for magnetic-fields µ0H applied along its inter-layer direction. Surprisingly, large anomalous transport coefficients are also observed for µ0H applied along the planar a-axis as well as along the gradient of the chemical potential generated by thermal gradients or electrical currents, a configuration that should not lead to their observation due to the absence of Lorentz force. However, as µ0H //a-axis is increased, magnetization and neutron scattering indicate just the progressive canting of the magnetic moments towards the planes followed by their saturation. These anomalous planar quantities are found to not scale with the component of the planar magnetization (Mk), showing instead a sharp decrease beyond ∼ µ0H// = 4 T which is the field required to align the magnetic moments along µd0^H//. We argue that locally chiral spin structures, such as skyrmions, and particularly spin spirals under planar fields, lead to a field dependent spin-chirality. In turn, this generates a novel type of topological transport in the absence of interaction between the magnetic field and electrical or thermal currents. Locally chiral spin-structures are captured by our Monte-Carlo simulations incorporating small Dzyaloshinskii-Moriya and biquadratic exchange interactions. These observations reveal not only a new way to detect and expose topological excitations, but also a new configuration for heat conversion that expands the current technological horizon for thermoelectric energy applications.
Applied Physics Reviews


magnetism, topology, 2D materials, skyrmions, neutron diffraction, anomalous Hall effect


Macy, J. , Ratkovski, D. , Balakrishnan, P. , Strungaru, M. , Chiu, Y. , Flessa, A. , Moon, A. , Zheng, W. , Weiland, A. , McCandless, G. , Chan, J. , Kumar, G. , Shatruk, M. , Grutter, A. , Borchers, J. , Ratcliff, W. , Choi, E. , Santos, E. and Balicas, L. (2021), Magnetic Field-Induced Non-Trivial Electronic Topology in Fe<sub>3&#8722;x</sub>GeTe<sub>2</sub>, Applied Physics Reviews, [online],, (Accessed December 8, 2021)
Created October 7, 2021