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

Published

October 7, 2021

Author(s)

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

Abstract

The anomalous Hall, Nernst and thermal Hall coefficients of the itinerant ferromagnet Fe_3−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 Fe_3−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 µ}d0^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.

Citation

Applied Physics Reviews

Volume

8

Issue

4

Pub Type

Journals

Download Paper

https://doi.org/10.1063/5.0052952

Local Download

Keywords

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

Citation

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_3−xGeTe₂, Applied Physics Reviews, [online], https://doi.org/10.1063/5.0052952, https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=932880 (Accessed November 21, 2024)