Magnetic Circular Dichroism Study of Electronic Transition in Metal Fe₃GeTe₂

Fe₃GeTe₂ (FGT) is one of the most attractive two-dimensional (2D) magnetic metals owing to the long-range ferromagnetic order and high Curie temperature. The electronic transition is of great importance for understanding the magnetic physics and spintronic applications in FGT. Although the ferromagnetic properties of FGT are well known, the band structure and electronic transition in both theory and experiment have been rarely studied. Here, we use density functional theory (DFT) and the magnetic circular dichroism (MCD) technique to study the electronic transition and phase transition of magnetic FGT. The electronic transitions at energy of 1.6 and 2.2 eV were observed through the reflection spectrum, which are further evidenced by first-principles calculations. At the critical temperature (170 K) where the ferromagnetic to paramagnetic phase transition happens, the interband electronic transition at 2.2 eV vanishes due to the disappearance of flat bands between the Γ-M point. Besides, a step appears in the hysteresis loop at the magnetic field of ±0.07 T where both the MCD and reflection spectrum also undergo an obvious change. This work has correlated the phase transition with electronic transition, offering a new degree of freedom to study the magnetic physics of ferromagnetic metals.