Critical Behavior of Cobalt-doped van der Waals Ferromagnet (Fe0.74Co0.26)3GeTe2

Abstract

Two-dimensional (2D) van der Waals (vdW) ferromagnet Fe₃GeTe₂ (FGT) demonstrates considerable potential for applications in spintronics due to its relatively high Curie temperature (T_C) and strong perpendicular magnetic anisotropy. Moreover, these demanding magnetic properties are sensitive to the Fe contents and can be effectively tuned by substituting Fe with other elements, especially the cobalt (Co) doping. Here, we delve into the magnetic critical behavior of the Co-doped vdW ferromagnet (Fe_0.74Co_0.26)₃GeTe₂ (FCGT). Utilizing a range of techniques including modified Arrott plots, Widom scaling method, the Kouvel-Fisher approach, and critical isotherm analysis, we derived reliable and self-consistent critical exponents: β = 0.360, γ = 1.043, δ = 3.87, with a T_C of 134.3 K. These critical exponents of FCGT do not conform to a single theoretical model but instead lie between the Mean-field model and the three-dimensional Heisenberg one. Despite the distinct critical exponents, Co doping does not alter the critical behavior intrinsic to the FGT. Further investigation implies the FCGT sustains long-range magnetic interactions, as evidenced by the magnetic exchange distance decay of J(r) ≈ r^-4.566. Our work could offer insights for the understanding of the macroscopic magnetic behavior of vdW ferromagnets doped with other transition metals.