Pervasive beyond Room-Temperature Ferromagnetism in a Doped van der Waals Magnet

Abstract

Two-dimensional (2D) magnetic van der Waals materials provide a powerful platform for studying fundamental physics of low-dimensional magnetism, engineering novel magnetic phases, and enabling ultrathin 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 Fe5GeTe2 (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. This corresponds to one of the thinnest room-temperature 2D magnet flakes exfoliated from robust single crystals, reaching a thickness relevant to practical spintronic applications.The Curie temperature Tc 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 Tc ~270 K in CFGT monolayers. Pathways towards further enhancing monolayer Tc are discussed. These results support CFGT as a promising platform to realize high-quality room-temperature 2D magnet devices. IntroductionReceived: ((will be filled in by the editorial staff))Revised: ((will be filled in by the editorial staff))

Layer-Number-Dependent Magnetism and Anomalous Hall Effect in van der Waals Ferromagnet Fe5GeTe2

“…Bulk Fe 5 GeTe 2 crystals exhibit multiple-step magnetic transitions with decreasing temperature ( T ). − , Determined from the sudden increase in the T -dependent magnetization ( M ) measured under a small magnetic field ( H ) of 50 Oe, the T c in our samples is 313 ± 5 K (Figure c). Recent work shows that the T c can be significantly enhanced via partial replacement of Fe by Ni . At around 120 K, another feature appears on M as manifested by a prominent slope change for H || ab (Figure c); correspondingly, the resistivity curve (Figure b) shows a remarkable decrease at the same temperature.…”

“…Recent work shows that the T c can be significantly enhanced via partial replacement of Fe by Ni. 16 At around 120 K, another feature appears on M as manifested by a prominent slope change for H || ab (Figure 1c); correspondingly, the resistivity curve (Figure 1b) shows a remarkable decrease at the same temperature. These observations suggest a second magnetic transition taking place at T* ∼ 120 K, which has been identified as the ordering temperature of the Fe1 sublattice (whereas Fe2 and Fe3 moments order at T c ≈ 313 K); 14,17 this transition at T* is also revealed to be strongly coupled to the lattice 14,17 and coincides with a Lifshitz transition in the electronic structure 18 and thus has a significant impact on the charge transport.…”

Controllable Topological Magnetic Transformations in the Thickness-Tunable van der Waals Ferromagnet Fe5GeTe2

“…The properties of 2D magnets, such as the Fe n GeTe 2 ( n = 3, 4, 5) family, − CrI 3 , − and Cr 2 Ge 2 Te 6 , , persist even down to thicknesses of one or several monolayers, , which could push magnetic memory information storage to the atomically thin limit. Among these vdW ferromagnets, Fe 5 GeTe 2 (FGT) was reported to possess a relatively high Curie temperature (270–310 K) − and large saturation magnetization (∼700 kA/m), exhibiting prospects as a candidate for room-temperature 2D vdW devices.…”

Magnetic Skyrmions with Unconventional Helicity Polarization in a Van Der Waals Ferromagnet

“…Another recent study reported a record high T c of 478 K in Ni‐doped Fe 5 GeTe 2 . [ 85 ] All the results reveal that Fe 5 GeTe 2 is an ideal platform to realize high‐temperature skyrmions with tunable spin topology.…”