Two-Dimensional Itinerant Ising Ferromagnetism in Atomically thin Fe3GeTe2

TL;DR

This paper reports the discovery of monolayer Fe3GeTe2 as a robust 2D itinerant ferromagnet with strong out-of-plane anisotropy, demonstrating a crossover from 3D to 2D Ising ferromagnetism and revealing unique magnetic behaviors at different thicknesses.

Contribution

It introduces monolayer Fe3GeTe2 as a new 2D itinerant ferromagnetic metal with strong perpendicular anisotropy, filling a gap in 2D magnetic materials.

Findings

Monolayer Fe3GeTe2 exhibits 2D Ising ferromagnetism with a Curie temperature of 130 K.

A crossover from 3D to 2D ferromagnetism occurs below 4 nm thickness.

Labyrinthine domain patterns form in flakes thicker than ~15 nm.

Abstract

Recent discoveries of intrinsic two-dimensional (2D) ferromagnetism in insulating/semiconducting van der Waals (vdW) crystals open up new possibilities for studying fundamental 2D magnetism and devices employing localized spins. However, a vdW material that exhibits 2D itinerant magnetism remains elusive. In fact, the synthesis of such single-crystal ferromagnetic metals with strong perpendicular anisotropy at the atomically thin limit has been a long-standing challenge. Here, we demonstrate that monolayer Fe3GeTe2 is a robust 2D itinerant ferromagnet with strong out-of-plane anisotropy. Layer-dependent studies reveal a crossover from 3D to 2D Ising ferromagnetism for thicknesses less than 4 nm (five layers), accompanying a fast drop of the Curie temperature from 207 K down to 130 K in the monolayer. For Fe3GeTe2 flakes thicker than ~15 nm, a peculiar magnetic behavior emerges within an intermediate temperature range, which we show is due to the formation of labyrinthine domain patterns. Our work introduces a novel atomically thin ferromagnetic metal that could be useful for the study of controllable 2D itinerant Ising ferromagnetism and for engineering spintronic vdW heterostructures.