Gd impurity effect on the magnetic and electronic properties of hexagonal Sr ferrites: A case study by DFT

The electronic and magnetic properties of strontium hexa-ferrite (SrFe₁₂O₁₉) are studied in pure state (SrFe₁₂O₁₉) and with dopant in the positions 2 and 3 of Fe atoms (SrGdFe₁₁O₁₉-I and SrGdFe₁₁O₁₉-II, respectively) by utilizing a variety of the density functional theory (DFT) approaches including the Perdew–Burke–Ernzerhof generalized gradient approximation (PBE-GGA) and GGA plus Hubbard U parameter (GGA+U). The pure SrFe₁₂O₁₉ is a hard magnetic half-metal with an integer magnetic moment of 64.00μ _B, while using the GGA+U functional, the magnetic intensity increases, resulting in a magnetic semiconductor with a high integer magnetic moment of 120μ _B. By doping the Gd atom in the two different positions of Fe, the magnetic moment is increased to 71.68μ _B and 68.00μ _B, respectively. The magnetic moment increases and remains an integer; hence, SrGdFe₁₁O₁₉-II can be very useful for application in magnetic memories. Moreover, applying the Hubbard parameter turns SrGdFe₁₁O₁₉-I and SrGdFe₁₁O₁₉-II to magnetic semiconductors with a magnetic moment of 124μ _B, and the energy gap of both doped structures at spin down is found to be less than the pure case. By studying the electronic density diagram of the atoms of the crystal, it is found that the major effect to create magnetization in the pure case is due to the Fe atom. However, in the doped case, the elements Gd and Fe have the highest moment in the crystal respectively. (paper)