Possible magnetic correlation above the ferromagnetic phase transition temperature in Cr₂Ge₂Te₆

Cr₂Ge₂Te₆ has recently emerged as a new two-dimensional ferromagnetic semiconductor (2DFMS) that is promising for spintronic applications. The origin of the ferromagnetism is a debatable point. In this study, ac/dc susceptibility and electronic spin resonance (ESR) measurements are performed to explore the origin of the ferromagnetism in Cr₂Ge₂Te₆. Through the ac susceptibility scaling, the critical temperature T_C = 62.84 K and δ = 5.24 from the critical isotherm, γ + β = 1.78 from the temperature dependence of the crossover line and γ = 1.43 from the temperature dependence of the susceptibility along the same line. Unlike Cr₂Si₂Te₆ whose magnetism can be well described by the 2D-Ising model, Cr₂Ge₂Te₆ cannot be simply described by a single theory model. Meanwhile, the origin of the abnormal critical behavior has been explored and it may be related to the presence of the possible magnetic correlation around the high temperature T* ∼ 160 K, which is confirmed by different probing measurements. The magnetic correlation at high temperature accompanied by the strong magnetic-crystalline anisotropy at low temperature plays an important role in the origin of the abnormal ferromagnetism in Cr₂Ge₂Te₆. Our results may supply a typical reference to investigate the abnormal ferromagnetism of 2DFMSs.