Patterning-Induced Ferromagnetism of Fe₃GeTe₂ van der Waals Materials beyond Room Temperature

Abstract

Magnetic van der Waals (vdW) materials have emerged as promising candidates for spintronics applications, especially after the recent discovery of intrinsic ferromagnetism in monolayer vdW materials. There has been a critical need for tunable ferromagnetic vdW materials beyond room temperature. Here, we report a real-space imaging study of itinerant ferromagnet FeGeTe and the enhancement of its Curie temperature well above ambient temperature. We find that the magnetic long-range order in FeGeTe is characterized by an unconventional out-of-plane stripe-domain phase. In FeGeTe microstructures patterned by a focused ion beam, the out-of-plane stripe domain phase undergoes a surprising transition at 230 K to an in-plane vortex phase that persists beyond room temperature. The discovery of tunable ferromagnetism in FeGeTe materials opens up vast opportunities for utilizing vdW magnets in room-temperature spintronics devices.

The van der Waals Ferromagnets Fe5–δGeTe2 and Fe5–δ–xNixGeTe2 – Crystal Structure, Stacking Faults, and Magnetic Properties

“…Nevertheless, thin films of Cr 2 Ge 2 Te 6 , Fe 3 GeTe 2 , and FePS 3 for example show intrinsic ferromagnetism or antiferromagnetism, which leads to good prospects in spintronic device applications. [2a], The high Curie temperature of 220 K and strong anisotropy of the magnetic state favors Fe 3 GeTe 2 over other ferromagnetic van der Waals materials . The hexagonal structure of Fe 3 GeTe 2 contains metal atom substructures sandwiched by tellurium layers building the van der Waals gap …”

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 .…”

“…The typical Curie temperatures of 2D‐vdW magnets are much lower than room temperature, and this figure of merit is largely limited by exchange interaction and magnetic anisotropy, according to the Mermin‐Wagner theorem. The group of Qiu et al has demonstrated an increase in the Curie temperature associated with FGT flakes by magnetic domain engineering . Figure D displays the magnetic domain images for unpatterned, micro‐sized diamond‐shaped and rectangular patterned structures at 300 K. Unlike the unpatterned FGT flakes with a single domain configuration, the in‐plane magnetization component within the patterned FGT microstructures not only remains but also develops into a magnetic vortex state in the diamond‐shaped microstructures and a magnetic domain state in the rectangular structure, respectively.…”

“…F I G U R E 4 A, Crystal structure of Fe 3 GeTe 2 (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 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).…”