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MA: Magnetismus

MA 4: Magnetic Materials I

MA 4.2: Vortrag

Montag, 27. März 2006, 10:30–10:45, HSZ 401

Correlation in the transition metal based Heusler compounds Co₂MnSi and Co₂FeSi — •Hem Chandra Kandpal, Gerhard H. Fecher, and Claudia Felser — Johannes Gutenberg - Universität, 55099 Mainz, Germany

Half-metallic ferromagnets like the full Heusler compounds are supposed to show an integer value of the magnetic moment. Calculations reveal for Co₂FeSi a non-integer value, in contrast to experiments. In order to explain deviations of the calculated magnetic moment, the dependency of the electronic structure on the lattice parameter was studied theoretically. In LSDA, the minimum total energy of Co₂FeSi is found for the experimental lattice parameter, but the calculated magnetic moment is about 12% too low. Half-metallic ferromagnetism and a magnetic moment equal to the experimental value of 6µ_B are found, however, only after increasing the lattice parameter by more than 6%.

To overcome this discrepancy, the LDA+U scheme was used to include electron correlation in the calculations. The calculations revealed that an effective Coulomb-exchange interaction U_eff=U−J in the range of about 2eV to 5eV leads to half-metallic ferromagnetism and the measured, integer magnetic moment at the measured lattice parameter. Finally, it is shown in the case of Co₂MnSi that correlation may also serve to destroy the half-metallic behaviour if it becomes too strong (for Co₂MnSi above 2eV and for Co₂FeSi above 5eV). These findings indicate that on-site correlation may play an important role in the description of Heusler compounds with localized moments. (This work is funded by the DFG in FG 559.)