Investigation on the structural, electronic, magnetic, and magnetic anisotropy energies of the CoGe (001) thin films: A Comparative DFT and DFT + U Study

The thickness dependence structural, electrical, and magnetic characteristics of CoGe (001) thin films have been extensively investigated theoretically. The computed negative formation energies per formula unit indicate that CoGe(001) thin films can be synthesised experimentally. The spin-polarized calculation on two to five layers (B to E) have shown that spin magnetic moments are turned on and off. However, inclusion of the on-site Coulomb interaction term U=3 eV (J=1 eV) has revealed that all systems are stable in the ferromagnetic phase with an augmentation of spin magnetic moment per Co atom and unit cell. The conventional Density functional theory (DFT) method predicts that calculated thin films are metallic. In the DFT+U calculation, systems B, C, and E are metallic, while system D has separate spin-down and spin-up bands at Fermi level. Moreover, band inversion in spin-up bands is also observed. The inclusion of spin-orbit coupling (SOC) does not affect to the magnetic moments of Co atom and of unit cell. All the systems have magnetic anisotropy energy (MAE) remains in-plane within DFT but changes out of the plane with DFT+U except system B. These findings may benefit and promise the Ge-based spintronics sector.