Unusual magnetotransport and anomalous Hall effect in quasi-two-dimensional van der Waals ferromagnet Fe$_4$GeTe$_2$

Riju Pal; Buddhadeb Pal; Suchanda Mondal; Prabhat Mandal; Atindra Nath Pal

doi:10.1038/s41699-024-00463-y

paper

Unusual magnetotransport and anomalous Hall effect in quasi-two-dimensional van der Waals ferromagnet Fe $_{4}$ GeTe $_{2}$

arXiv:2303.07440 · doi:10.1038/s41699-024-00463-y

Abstract

Fe $_{4}$ GeTe $_{2}$ , an itinerant vdW ferromagnet (FM) having Curie temperature (T $_{C}$ ) close to room temperature ( $\sim 270$ K), exhibits another transition (T $_{S R}$ $\sim$ 120 K) where the easy axis of magnetization changes from in-plane to the out-of-plane direction in addition to T $_{C}$ . Here, we have studied the magnetotransport in a multilayer Hall bar device fabricated on 300 nm Si/SiO $_{2}$ substrate. Interestingly, the zero field resistivity shows a negligible change in resistivity near T $_{C}$ unlike the typical metallic FM, whereas, it exhibits a dramatic fall below T $_{S R}$ . Also, the resistivity shows a weak anomaly at T $\sim$ 38 K (T $_{Q}$ ), below which the resistivity shows a quadratic temperature dependence according to the Fermi liquid behavior. Temperature-dependent Hall data exhibits important consequences. The ordinary Hall coefficient changes sign near T $_{S R}$ indicating the change in majority carriers. In a similar manner, the magnetoresistance (MR) data shows significantly large negative MR near T $_{S R}$ and becomes positive below T $_{Q}$ . The observations of anomaly in the resistivity, sign-change of the ordinary Hall coefficient and maximum negative MR near T $_{S R}$ , together suggest a possible Fermi surface reconstruction associated with the spin reorientation transition. Furthermore, analysis of the Hall data reveals a significant anomalous Hall conductivity (AHC) from $\sim 123 Ω^{- 1}$ cm $^{- 1}$ (at T $\approx$ 5 K) to the maximum value of $\sim 366 Ω^{- 1}$ cm $^{- 1}$ near T $_{S R}$ . While the low-temperature part may originate due to the intrinsic KL mechanism, our analysis indicates that the temperature-dependent AHC is primarily appearing due to the side-jump mechanism as a result of the spin-flip electron-magnon scattering. Our study demonstrates an interplay between magnetism and band topology and its consequence on electron transport in Fe $_{4}$ GeTe $_{2}$ .

Main Text: 10 pages, 5 figures ; Supplementary Material: 9 pages, 8 figures

Unusual magnetotransport and anomalous Hall effect in quasi-two-dimensional van der Waals ferromagnet Fe $_{4}$ GeTe $_{2}$

Abstract

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Unusual magnetotransport and anomalous Hall effect in quasi-two-dimensional van der Waals ferromagnet Fe4​GeTe2​

Abstract

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Unusual magnetotransport and anomalous Hall effect in quasi-two-dimensional van der Waals ferromagnet Fe $_{4}$ GeTe $_{2}$