Double perovskites with high spin polarization
Final Report Abstract
This project investigated the synthesis of new materials with high spin polarization and high Curie temperature of polycrystalline bulk double perovskites that were predicted to be half-metallic with composition Sr2MM’O6 (M = Fe, Cr, Ga and M’ = Mo, Re). In addition to the substituted solid solutions, we also studied some of the end members such as Sr2GaReO6, Sr2InReO6, Sr4Fe3ReO12, Sr4Fe2ReGaO12. In the framework of the tight-binding approach, hole- or electron-doping of Sr2MM’O6 were performed at the M or M’ positions either by transition or main group metals. Hole-doping, rather than electron doping, has a favorable effect to improve the half-metallicity (Curie temperature and saturation magnetization) of the parent compound. When M is substituted by another metal, the original M’ metal will serve as a redox buffer (and vice versa). Substituting M by another metal with a size similar to that of the metal at M´ position causes disorder, which has high impact on the properties of the starting compound. Main group metals block the super-exchange pathways that underlie the half-metallic properties in Sr2FeReO6. Thus, a Mott-insulating and spin-frustrated state is produced in an ordered phase due to the geometrical arrangement, e.g. in Sr2InReO6. However, M/M’ disorder is significant in the main group elements containing double perovskites, this triggers electronic conductivity arising from electron hopping from Re to adjacent Re ions as observed in Sr2GaReO6. Some Re-containing double perovskites (e.g. Sr2InReO6, Sr2GaReO6, Sr4Fe3ReO12 etc.) are easily predicted to be a “half-metal”, even in some case that electron correlation is taken into account. Therefore special treatments (e.g. Spin-orbit plus Hubbard U, ect.) need to be undertaken to avoid such a trap. Following this clue, we extended this study to other 4d, 5d, 4f transition elements containing double perovskites with a closed shelled element sitting on their adjacent M/M’ positions. We found that these compounds are mostly “pseudo halfmetallic” by either GGA or GGA + Hubbard U. Cooperative effect of spin-orbit coupling and Hubbard U was found to be a good approach to reproduce their real semiconducting nature.
Publications
- (2005): Structural and magnetic properties of the solid solution series Sr2Fe1–xMxReO6(M = Cr, Zn). In: J. Mater. Chem. 15 (17), S. 1760
A. Jung, I. Bonn, V. Ksenofontov, G. Melnyk, J. Ensling, C. Felser, W. Tremel
(See online at https://doi.org/10.1039/B414182B) - (2006): Magnetic transitions in double perovskite Sr2FeRe1−xSbxO6(0⩽x⩽0.9). In: Phys. Rev. B 73 (14), S. 144414
A. Jung, V. Ksenofontov, S. Reiman, C. Felser, W. Tremel
(See online at https://doi.org/10.1103/PhysRevB.73.144414) - (2007): Effect of cation disorder on the magnetic properties of Sr2Fe1−xGaxReO6(0
A. Jung, I. Bonn, V. Ksenofontov, M. Panthöfer, S. Reiman, C. Felser, W. Tremel
(See online at https://doi.org/10.1103/PhysRevB.75.184409)
