Two-dimensional itinerant ferromagnetism in atomically thin Fe3GeTe2

Abstract

Discoveries of intrinsic two-dimensional (2D) ferromagnetism in van der Waals (vdW) crystals provide an interesting arena for studying fundamental 2D magnetism and devices that employ localized spins. However, an exfoliable vdW material that exhibits intrinsic 2D itinerant magnetism remains elusive. Here we demonstrate that FeGeTe (FGT), an exfoliable vdW magnet, exhibits robust 2D ferromagnetism with strong perpendicular anisotropy when thinned down to a monolayer. Layer-number-dependent studies reveal a crossover from 3D to 2D Ising ferromagnetism for thicknesses less than 4 nm (five layers), accompanied by a fast drop of the Curie temperature (T) from 207 K to 130 K in the monolayer. For FGT flakes thicker than ~15 nm, a distinct magnetic behaviour emerges in an intermediate temperature range, which we show is due to the formation of labyrinthine domain patterns. Our work introduces an atomically thin ferromagnetic metal that could be useful for the study of controllable 2D itinerant ferromagnetism and for engineering spintronic vdW heterostructures.

Fe5−xGe2Te2—a New Exfoliable Itinerant Ferromagnet with High Curie Temperature and Large Perpendicular Magnetic Anisotropy

“…The FG2T resistivity corresponds to metallic behavior, as predicted earlier by DFT. Similar resistivity values at 300 K have been reported for FGT (648 and 440 μΩ cm[9b]) and Fe 5− x GeTe 2 (300 μΩ cm[14b]). FG2T is therefore a FM metal, as predicted by DFT.…”

Van der Waals magnets: Wonder building blocks for two‐dimensional spintronics?

“…A, Crystal structure of Fe 3 GeTe 2 (FGT) . B, Polar RMCD signal for a monolayer FGT at several fixed temperatures . C, Thickness‐temperature phase diagram for three distinct magnetic states: paramagnetic (PM), single domain ferromagnetic (FM1) and labyrinthine domain ferromagnet (FM2) .…”

“…The group of Xu et al has reported intrinsic itinerant magnetism in exfoliated 2D-FGT, by means of low-temperature electrical transport and RMCD measurements. 81 Figure 4B shows the polar RMCD signal as a function of magnetic field for monolayer FGT at several temperatures. With increasing temperature, the hysteresis shrinks accordingly and disappears at 130 K, indicating the Curie temperature for monolayer FGT.…”

“…80 B, Polar RMCD signal for a monolayer FGT at several fixed temperatures. 81 C, Thickness-temperature phase diagram for three distinct magnetic states: paramagnetic (PM), single domain ferromagnetic (FM1) and labyrinthine domain ferromagnet (FM2). 81 D, Magnetic domain images for unpatterned, micro-sized diamond-shaped and rectangular patterned structures at 300 K. 80 E, Schematic of the FGT device structure and measurement set up (left panel).…”

“…81 C, Thickness-temperature phase diagram for three distinct magnetic states: paramagnetic (PM), single domain ferromagnetic (FM1) and labyrinthine domain ferromagnet (FM2). 81 D, Magnetic domain images for unpatterned, micro-sized diamond-shaped and rectangular patterned structures at 300 K. 80 E, Schematic of the FGT device structure and measurement set up (left panel). 82 F, Phase diagram of the trilayer FGT samples as a function of magnetic field and temperature at a gate voltage of 2.1 V (right panel).…”