Investigation of Fe antisite disorder in FexGa3−x under high pressure.*

FeGa3 is a strongly correlated narrow-gap semiconductor candidate and has been widely studied because of its unconventional magnetic and electronic properties and as promising thermoelectric material. The crystal structure of FeGa3 is tetragonal P42/mnm, where Ga atoms surround Fe atoms in a manner that it resembles other semiconductors with a type-cage structure. An intrinsic small energy gap ? opens at the Fermi energy level (Ef ) (? ≈ 0.4 eV), suggesting that strong electronic correlations disturb the Fe-3d-Ga-4p hybridization, Coulomb repulsion, and Ef . The competition between these low-lying energy scales sets the ground state of FeGa3 as a Kondo-insulator-like semiconductor with a diamagnetic ground state. The substitution of Ge in a solid solution FeGa3−yGey shows that FeGa3 can be tuned to a putative ferromagnetic quantum critical point (FM-QCP) around y = 0.15. However, the coexistence between long- and short-range magnetic order above xc suggests that disorder induced by random Ge substitution plays an important role in the zero temperature phase transition. It is noteworthy that deviations from the electronic and magnetic ground states expected in pristine semiconductor FeGa3 can be tuned by controlled disorder which can induce the formation of a complex structure of metallic in-gap states responsible for forming magnetic moments in the ground state.

To investigate the intertwining between disorder and electronic correlations, we have recently synthesized FeGa3 with the inclusion of controlled antisite Fe disorder as a compound named Fe1+δGa3 (δ = 0.16). The antisite Fe disorder is quantified by deviations in the occupancy number of Fe and Ga sites which changes the in-gap semiconducting and magnetic states of the pristine compound.

We have also investigated FeGa3 under the efect of compression and hydrostatic pressure. Our results show that pressure reduces the in-gap activation energy (Eg) of the impurity states while enhancing the magnetic ordering temperature (Tm). In addition, pressure increases sizeable the Sommerfeld coefficient γ. Because γ is a signature of the electronic density of the states population, our results might indicate that pressure acts as a control parameter to strengthen the electronic hybridization and to narrow the electronic bandwidth of the in-gap states.