Dresden 2014 – wissenschaftliches Programm

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MA: Fachverband Magnetismus

MA 51: Electron Theory of Magnetism

MA 51.2: Vortrag

Freitag, 4. April 2014, 09:45–10:00, HSZ 401

Exchange interactions and Curie temperature of MnSi: A density functional study — •Giovanna Lani, Phivos Mavropoulos, Gustav Bihlmayer, and Stefan Blügel — Peter Grünberg Institut and Institute for Advanced Simulation, Forschungszentrum Jülich and JARA, D-52425 Jülich, Germany

We present a theoretical investigation of zero and finite temperature properties of bulk MnSi in the B20 structure. MnSi is known to pose a theoretical challenge, as its magnetic moment is overestimated by a factor two within the LDA and GGA approximations to DFT. Therefore, employing two different all-electron approaches, namely the FLAPW and KKR methods, we investigate how constraining the magnetic moment to the experimental value affects the electronic structure of MnSi. By mapping the results of DFT calculations onto a Heisenberg Hamiltonian, we extract the exchange parameters. We find that they exhibit long-range oscillations and we argue that while some of their features are independent of the value of the magnetic moment, others are not and this can be attributed to changes in the Fermi surface topology as a function of the moment. The Curie temperature, estimated via a Monte Carlo method, agrees with the available measurements only when the moment is constrained to the experimental value. This finding is further validated by including longitudinal moment fluctuations within a static mean field theory with a KKR-CPA disordered local moment calculation in the spirit of the Hubbard III approximation.