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

Abstract Two-dimensional (2D) ferromagnets with high Curie temperature T C 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 T C values are below room temperature. Using first-principles calculations, we design a family of stable 2D Fe n GeTe 2 (4 ≤ n ≤ 7) ultrathin films with coexisting itinerant and localized magnetism. Among them, 2D Fe 3 GeTe 2 and Fe 4 GeTe 2 are ferromagnetic metals with T C = 138 and 68 K; 2D Fe 5 GeTe 2 , Fe 6 GeTe 2 , and Fe 7 GeTe 2 are Néel’s P-, R-, and R-type ferrimagnetic metals with T C = 320, 450, and 570 K. A thickness-induced magnetic phase transition originates from competition between itinerant and localized states, and also correlates with Fe 3+ and Fe 2+ 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.