References of "Ricci, Fabio"
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See detailDoping effects and magnetic instabilities in Full-Heusler Fe2YZ1-xAx
Lemal, Sébastien ULiege; Ricci, Fabio ULiege; Verstraete, Matthieu ULiege et al

Conference (2019, March 08)

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See detailThe second-principles MULTIBINIT software project
Ricci, Fabio ULiege; Martin, Alexandre; Garcia Castro, Andrés Camilo et al

Conference (2019, March 08)

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See detailDensity functional perturbation theory within noncollinear magnetism
Ricci, Fabio ULiege; Prokhorenko, Sergei ULiege; Torrent, Marc et al

in Physical Review. B (2019), 99

We extend the density functional perturbation theory formalism to the case of noncollinear magnetism. The main problem comes with the exchange-correlation (XC) potential derivatives, which are the only ... [more ▼]

We extend the density functional perturbation theory formalism to the case of noncollinear magnetism. The main problem comes with the exchange-correlation (XC) potential derivatives, which are the only ones that are affected by the noncollinearity of the system. Most of the present XC functionals are constructed at the collinear level, such that the off-diagonal (containing magnetization densities along x and y directions) derivatives cannot be calculated simply in the noncollinear framework. To solve this problem, we consider here possibilities to transform the noncollinear XC derivatives to a local collinear basis, where the z axis is aligned with the local magnetization at each point. The two methods we explore are (i) expanding the spin rotation matrix as a Taylor series and (ii) evaluating explicitly the XC for the local density approximation through an analytical expression of the expansion terms. We compare the two methods and describe their practical implementation. We show their application for atomic displacement and electric field perturbations at the second order, within the norm- conserving pseudopotential methods. [less ▲]

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See detailThe second-principles MULTIBINIT software project
Ricci, Fabio ULiege; Martin, Alexandre ULiege; García Castro, Andrès Camilo ULiege et al

Conference (2018, September 20)

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See detailThermoelectric properties of chemically substituted full-Heusler Fe2TiSn1-xSbx (x = 0, 0.1, and 0.2) compounds
Pallecchi, Ilaria; Pani, Marcella; Ricci, Fabio ULiege et al

in Physical Review Materials (2018), 2

According to theoretical predictions [Phys. Rev. Lett. 114, 136601 (2015)], Sb substitution in Fe2TiSn full-Heusler compounds is thought to enhance the n-type thermoelectric power factors. We prepare ... [more ▼]

According to theoretical predictions [Phys. Rev. Lett. 114, 136601 (2015)], Sb substitution in Fe2TiSn full-Heusler compounds is thought to enhance the n-type thermoelectric power factors. We prepare Fe2TiSn samples with 0%, 10%, and 20% Sb substitution on the Sn site and study the effects of the heat treatment protocol and of Sb substitution by structural characterization, electrical, thermoelectrical, and thermal transport measurements from room temperature down to 10 K, and by comparison with ab initio calculations. For the undoped Fe2TiSn phase, we find a bad metallic gapless transport behavior in the as-cast sample and a small gap semiconducting behavior for the annealed samples. These observations, together with the p-type character emerging from the Hall effect and Seebeck effect, are explained by ab initio calculations, provided that antisite disorder and vacancy defects are included. In these undoped Fe2TiSn samples, we find that increasing thermal annealing temperature up to 800 °C slightly decreases the carrier concentration, enhances the Seebeck coefficient in the low-temperature regime (below 100–200 K), induces magnetic ordering at low temperature (<150 K), and improves the thermoelectric figure of merit and power factor in the low-temperature regime (below ∼200 K). As for Sb substitution, we find that 10% substitution increases hole carrier concentration and induces a weakly metallic behavior as compared to the semiconducting behavior of the corresponding undoped annealed samples. On the other hand, 20% substitution lowers the carrier density and increases the resistivity by a factor ∼50, with semiconducting behavior measured in the whole temperature range. We interpret the observed effect of Sb doping as a complement to disorder. Indeed, using first-principles techniques we unearth the experimental signature related to density of states features induced by native impurities in the realized samples. The Seebeck coefficient exhibits a maximum at around 200–250 K for the undoped and 20%-doped samples, as typical of semiconducting compounds, while it increases monotonically with temperature for the metallic 10%-doped sample. The latter behavior, joined with the good electrical properties of the 10% sample, determines the room-temperature power factor of ∼1.3 × 10^−4 W K^−2 m −1 in the 10% Sb-doped sample, more than twice as much as to the value of the undoped sample. [less ▲]

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See detailThermoelectric properties of heavily-doped Fe2YZ full-Heusler compounds
Lemal, Sébastien ULiege; Ricci, Fabio ULiege; Verstraete, Matthieu ULiege et al

Poster (2017, July 31)

Fe2YZ full-Heusler compounds were recently predicted to exhibit very large thermoelectric power factors [Phys. Rev. Lett. 114, 136601 (2015)]. Combining first-principles density functional theory ... [more ▼]

Fe2YZ full-Heusler compounds were recently predicted to exhibit very large thermoelectric power factors [Phys. Rev. Lett. 114, 136601 (2015)]. Combining first-principles density functional theory calculations within a hybrid functional approach and Boltzmann semi-classical transport theory, we investigate the limits of the rigid band doping approximation, and the properties of heavily n-type doped full-Heusler Fe2YZ1-xAx compounds. Using a supercell approach and including explicit dopant impurities, we recover in some cases giant thermoelectric power factors, as previously predicted within the rigid band approximation. In others the effect on the electronic structure is very different from rigid shifts. Interestingly, we find that some systems present a magnetic instability consistent with the Stoner model, and evolve towards a ferromagnetic half-metallic ground state, with a strongly modified power factor. Our results show the promise of the heavily-doped phases of the studied Fe2YZ1-xAx compounds for Seebeck and spin-dependent Seebeck applications. [less ▲]

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See detailUnveiling the Room-Temperature Magnetoelectricity of Troilite FeS
Ricci, Fabio ULiege; Bousquet, Eric ULiege

in Physical Review Letters (2016), 116

We report on a first-principles study of the troilite phase of iron sulfide (FeS). We show that even if, a few decades ago, this material was thought to be ferroelectric, the structural transition from ... [more ▼]

We report on a first-principles study of the troilite phase of iron sulfide (FeS). We show that even if, a few decades ago, this material was thought to be ferroelectric, the structural transition from the high P63/mmc to the low P6¯2c symmetry phase does not involve polar instabilities, though the space inversion center symmetry is broken. Our calculations and symmetry analysis nevertheless reveal that FeS is magnetoelectric at room temperature with a response larger than the prototypical room-temperature magnetoelectric crystal Cr2O3. We also show that the spin channel decomposition of the polarization exhibits nonzero values in the opposite direction in FeS, which is actually a general hint of the presence of a magnetoelectric monopole in diagonal magnetoelectrics. [less ▲]

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