Layer-dependent magnetic phase diagram in FenGeTe2 (3 ≤ n ≤ 7) ultrathin films

Abstract

Two-dimensional (2D) ferromagnets with high Curie temperature TC are desirable for spintronics applications. However, they are rarely obtained in experiments mainly due to the challenge of synthesizing high-quality 2D crystals, and their TC values are below room temperature. Using first-principles calculations, we design a family of stable 2D FenGeTe2 (4 ≤ n ≤ 7) ultrathin films with coexisting itinerant and localized magnetism. Among them, 2D Fe3GeTe2 and Fe4GeTe2 are ferromagnetic metals with TC = 138 and 68 K; 2D Fe5GeTe2, Fe6GeTe2, and Fe7GeTe2 are Néel’s P-, R-, and R-type ferrimagnetic metals with TC = 320, 450, and 570 K. A thickness-induced magnetic phase transition originates from competition between itinerant and localized states, and also correlates with Fe3+ and Fe2+ content. A valence/orbital-dependent magnetic exchange model is proposed for these effects. Our results reveal a universal mechanism for magnetic coupling in complex magnetic systems.

Interfacial engineering of ferromagnetism in wafer-scale van der Waals Fe4GeTe2 far above room temperature

“…Recently, the emergence of Fe-rich vdW ferromagnets Fe n GeTe 2 received intense research interest due to their large magnetization near room temperature (for 3 ≤ n ≤ 5, T c = 220–310 K) 8 – 15 . In the family of Fe n GeTe 2 , Fe 4 GeTe 2 has been highlighted as a very promising candidate material for spintronics applications because of its relatively high T c (270 K) and flexible magnetic anisotropy 10 , 16 – 18 . In traditional vdW ferromagnetic materials (for instance, CrI 3 or Cr 2 Ge 2 Te 6 ), the magnetic atoms are encapsulated by nonmagnetic atoms and form a 2D magnetic system 19 , 20 .…”

Modulation of skyrmionic magnetic textures in two-dimensional vdW materials and their heterostructures

“… 73 In addition, the various stoichiometric ratios induce different crystal structures with different magnetic sublattices for 2D Fe n GeTe 2 , which influence magnetism. 74 , 75 The skyrmion bubbles have been observed in Fe 3 GeTe 2 and Fe 5 GeTe 2 . 17 , 76 It is highly anticipated that more effective modulations could be achieved to control SMTs.…”

“…For example, the formation of skyrmions was proposed in the CrI 3 monolayer by substituting I atoms with Cl atoms to break the inversion symmetry 73 . In addition, the various stoichiometric ratios induce different crystal structures with different magnetic sublattices for 2D Fe n GeTe 2 , which influence magnetism 74,75 . The skyrmion bubbles have been observed in Fe 3 GeTe 2 and Fe 5 GeTe 2 17,76…”

Recent Advances in 2D Material Theory, Synthesis, Properties, and Applications

“…Indeed, from Fe 3 GeTe 2 to Fe 5 GeTe 2 with thicknesses around 10 nm or thicker, T C was found to generally increase from about 220 K to about 300 K. These promising T C values are expected to further increase with increasing Fe content to values up to and even beyond 500 K . Recent theoretical studies also predicted that Fe 6 GeTe 2 and Fe 7 GeTe 2 are stable 2D phases . However, experimental validation is lacking.…”