Fig. 1: High-T_N antiferromagnetism of (Fe_0.54Co_0.46)₅GeTe₂ (FCGT).

a Crystallographic structure of FCGT viewed along the [110] direction. The red, green, and light purple spheres indicate Fe/Co, Ge, and Te atoms, respectively. Fe/Co 1 sites are half-filled, whereas Fe/Co 2 and 3 sites are fully occupied. The gray rectangle designates a unit cell. The schematic depicts the formation of a multilayered magnetic structure, i.e., A-type antiferromagnetic order. b Magnetic susceptibility, χ = M/H, measured upon warming under H = 0.05 T after zero-field cooling for H//c and H⊥c. The vertical dashed gray line specifies the Néel temperature, T_N = 350 K. c Isothermal magnetization measured for H//c (M_c) at T = 2 and 300 K. The red and orange inverted triangles denote the occurrence of spin-flop transitions, H_flop = 2.8 and 0.8 T for T = 2 and 300 K, respectively. d Calculated M_c for T = 2 and 300 K, estimated from a uniaxial anisotropic spin model. The schematics illustrate the angles of the magnetic moments (blue arrows) for the AFM, spin-flop, and spin-flip states at T = 2 K. The red arrows correspond to the strength of H_c. e Isothermal magnetization measured for H⊥c (M_ab) at T = 2 and 300 K. f Calculated M_ab for T = 2 and 300 K.