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conferenceseries
.com
Volume 08
Innovative Energy & Research
ISSN: 2576-1463
Advanced Energy Materials 2019
July 11-12, 2019
July 11-12, 2019 | Zurich, Switzerland
21
st
International Conference on
Advanced Energy Materials and Research
Magnetic instability in heavily n-doped Fe-based full Heusler compounds: Origin and impact on
thermoelectric properties
Fabio Ricci, Sébastien Lemal, Matthieu J Verstraete
and
Philippe Ghosez
University of Liège, Belgium
F
e
2
YZ full Heusler compounds, on which first principles on density functional theory (DFT) simulations predict
very large thermoelectric power factor (PF), are promising candidates for thermoelectric applications. The
building blocks of their interesting thermoelectric properties are the carriers belonging to the Fe-eg orbitals that
can be opportunely engineered to maximize PF. These anti-bonding states are represented by a flat band (mainly
composed of Fe dx
2
-y
2
character) along the ΓX direction of the Brillouin Zone, related to the highly directional Fe-
Fe bond, becoming dispersive along the other directions. This band satisfies the “flat-and-dispersive” requirements
proposed by Mahan and Sofo and leads to one-dimensional transport strongly enhancing the PF. However, due to
its strongly localized nature, explicit n-doping may induce a Stoner instability driving the system to a half-metallic
phase. The present study, performed through DFT using both hybrid functional and GGA+U methods on Fe
2
YZ
1-
x
A
x
(Y = Ti, V, Nb, Ta, Z=Al, Si, Sn, Ga and A=Si, P, Sb, Ge) n-doped systems, shows that the appearance of such a
magnetic phase is strictly linked to the Fe-eg and Y-site eg orbital hybridization and that it possesses a pure electronic
origin, independent on the dopant species. Although the Stoner instability can provide half-metallicity with coupled
thermomagnetic responses, the PF is typically reduced in the half-metallic phase due to a reduction of the number
of carriers available at the Fermi level. In certain cases, however, the values of the PF are still large (for Fe
2
TaGa
1-x
Ge
x
or Fe
2
TiSi
1-x
P
x
PF is between 9 and 15 10
-3
W K
-2
m
-1
at 600 K, for example) which stays promising for thermoelectric
applications. Going further, we elucidate the possibility to exploit the broader nature of 4d and 5d orbitals at the
bottom of the conduction band to overcome the magnetic phase appearance in the doping range of interest.
Biography
Fabio Ricci did his PhD on both simulations and experimental measurements on magnetic properties of materials (diluted magnetic semiconductors and soft
magnetic materials) by means of the magneto-optical Kerr effect. Subsequently, he worked on theoretical simulations on Fe-based superconductors, principally
iron-chalcogenides. He developed and implemented in the ABINIT code the formalism for the non-collinear magnetism in the density functional perturbation
theory and, at the same time, started to work on the theoretical engineering of thermoelectric properties of the Fe-based full-Heusler compounds.
fabio.ricci@uliege.beFabio Ricci et al., Innov Ener Res 2019, Volume 08