Above-Room-Temperature Ferromagnetism in Thin van der Waals Flakes of Cobalt-Substituted Fe₅GeTe₂

Abstract

Two-dimensional (2D) magnetic van der Waals materials provide a powerful platform for studying the fundamental physics of low-dimensional magnetism, engineering novel magnetic phases, and enabling thin and highly tunable spintronic devices. To realize high-quality and practical devices for such applications, there is a critical need for robust 2D magnets with ordering temperatures above room temperature that can be created via exfoliation. Here, the study of exfoliated flakes of cobalt-substituted Fe 5 GeTe 2 (CFGT) exhibiting magnetism above room temperature is reported. Via quantum magnetic imaging with nitrogen-vacancy centers in diamond, ferromagnetism at room temperature was observed in CFGT flakes as thin as 16 nm corresponding to 16 layers. This result expands the portfolio of thin roomtemperature 2D magnet flakes exfoliated from robust single crystals that reach a thickness regime relevant to practical spintronic applications. The Curie temperature T c of CFGT ranges from 310 K in the thinnest flake studied to 328 K in the bulk. To investigate the prospect of high-temperature monolayer ferromagnetism, Monte Carlo calculations were performed, which predicted a high value of T c of ∼270 K in CFGT monolayers. Pathways toward further enhancing monolayer T c are discussed. These results support CFGT as a promising platform for realizing high-quality room-temperature 2D magnet devices.

Near-room temperature ferromagnetism and a tunable anomalous Hall effect in atomically thin Fe4CoGeTe2

“…These are consistent with previous theoretical results. 32,34 For BL F4CGT, we found that the favorable substitution site is the same as the ML case, namely the Fe(1) site. Here the interlayer stacking of BL F4CGT could be AA-or AB-stacking.…”

“…26 More importantly, very recently the quantum magnetic imaging technique reveals that Co doped F5GT thin flakes with a thickness t of about 16 nm exhibit intrinsic ferromagnetism above room temperature (T C ∼ 310 K) at ambient pressure without ionic gating. 34 Moreover, Monte Carlo simulations predict that the monolayer (ML) of this material still has a near-room temperature T C (∼270 K). 34 In this work, we study the ferromagnetism of mechanically exfoliated Fe 4 CoGeTe 2 (F4CGT) thin flakes.…”

“…34 Moreover, Monte Carlo simulations predict that the monolayer (ML) of this material still has a near-room temperature T C (∼270 K). 34 In this work, we study the ferromagnetism of mechanically exfoliated Fe 4 CoGeTe 2 (F4CGT) thin flakes. From the measurements of the anomalous Hall resistivity, it is found that the T C of bulk materials (∼320 K) is almost intact when the thickness t > 12 nm and then decreases gradually for thinner samples, but the T C above 280 K can still be retained in the bilayer (BL) F4CGT (t ∼ 2 nm).…”

Cleavable crystals, crystal structure, and magnetic properties of the NbFe1+xTe3 layered van der Waals telluride

“…Layered vdW tellurides including CrSiTe 3 and CrGeTe 3 , 16–19 Fe 3 AsTe 2 , 20 Fe 3 GeTe 2 , 21,22 Fe 5 AsTe 2 , 23,24 Fe 5 GeTe 2 , 5,15,25–27 and TaFe 1+ x Te 3 28,29 are promising for the design of novel spintronic devices with tailored functionalities. The latter compound is distinguished by the peculiar crystal structure and interesting physical properties.…”

“…11 At the same time, Fe 5 GeTe 2 , which is ferromagnetic below 310 K, 5,[12][13][14] shows the efficient spin filtering within the Fe 5 GeTe 2 /graphene heterostructure already at room temperature. 15 Layered vdW tellurides including CrSiTe 3 and CrGeTe 3 , [16][17][18][19] Fe 3 AsTe 2 , 20 Fe 3 GeTe 2 , 21,22 Fe 5 AsTe 2 , 23,24 Fe 5 GeTe 2 , 5,15,[25][26][27] and TaFe 1+x Te 3 28,29 are promising for the design of novel spintronic devices with tailored functionalities. The latter compound is distinguished by the peculiar crystal structure and interesting physical properties.…”