Electronic structure, optical, and magneto-optical properties of Gd5(Si2Ge2) compound

The electronic structure, optical, and magneto-optical spectra of the strongly magnetocaloric Gd5(Si2Ge2) compound are investigated theoretically from first principles, using the fully relativistic Dirac linear muffin tin orbital band structure method. The electronic structure is obtained with the local spin-density approximation (LSDA), as well as with the so-called LSDA+U approach. The Coulomb repulsion Ueff strongly influences the electronic structure of Gd5(Si2Ge2) and for the Gd3+ ions seven spin up 4f bands are fully occupied and situated at the bottom of Si and Ge s states, while the 4f hole levels are completely unoccupied and well above the Fermi level hybridized with Gd 5d states. LSDA+U theory predicts that the magneto-optical spectra are much more sensitive to the α→β phase transition in comparison with the regular nonmagnetic optical properties.