Pressure-induced metal-insulator transition and absence of magnetic order in FeGa${}_3$ from a first-principles study

The intermetallic compound FeGa${}_3$ is a narrow-gap semiconductor with a measured gap between 0.2 and 0.6 eV. The presence of iron $d$ states on the top of the valence band and on the bottom of the conduction band, together with its moderate electronic correlation ($U/W\sim 0.6$), have led to the question of whether there is magnetic order in this compound. We have examined the possible presence of magnetism in FeGa${}_3$ as well as its electronic structure at high pressures, using the density functional theory (DFT) $+$ $U$ method with the intermediated double-counting scheme. We have found that for an optimized value of the Yukawa screening length $\lambda$, there is no magnetic moment on the iron ions ($\mu =0$), implying that FeGa${}_3$ is nonmagnetic. We have also found that around a pressure of 25 GPa a metal-insulator transition takes place.

Figure 1

(a) Calculated Hubbard parameter $U$ and intra-atomic exchange parameter $J$, (b) band gap $E_g$ and (c) magnetic moment per Fe ion $\mu$ as a function of the Yukawa screening length $\lambda$. The red square is the calculated band gap by means of GGA.

Figure 2

Calculated total energy per unit cell as a function of the magnetic moment per Fe ion. Red squares and blue diamonds are the obtained values for $\lambda =3.0$ and 2.5 a.u.${}^{-1}$, respectively.

Figure 3

Calculated equations of state (a) $E\left(\frac{\Omega }{{\Omega }_0}\right)$ and (b) $P\left(\frac{\Omega }{{\Omega }_0}\right)$, (c) magnetic moment per Fe ion, and (d) interionic distances for the Yukawa screening lengths $\lambda =3,2.5$ and $\lambda \to \infty$ (GGA). ${\Omega }_0$ is the experimental volume (Ref. 14).

Figure 4

Calculated electronic structure with $\lambda \to \infty$ (GGA) for different pressures. For $E\left(\mathbf{k}\right)$ the thick black lines correspond to Fe states, the thick red lines correspond to Ga${}_1$ states, and the thick green lines correspond to Ga${}_2$ states. The total DOS is denoted by a violet line, Fe $d$ states are denoted by a blue line, Ga $s$ states are denoted by an orange line, and Ga $p$ states are denoted by a turquoise line. The energy is shifted to the Fermi level.

Figure 5

Calculated electronic structure with $\lambda =3$ a.u.${}^{-1}$ for different pressures. For $E\left(\mathbf{k}\right)$ the thick black lines correspond to Fe states, the thick red lines correspond to Ga${}_1$ states, and the thick green lines correspond to Ga${}_2$ states. The total DOS is denoted by a violet line, Fe $d$ states are denoted by a blue line, Ga $s$ states are denoted by an orange line, and Ga $p$ states are denoted by a turquoise line. The energy is shifted to the Fermi level.

Figure 6

The calculated band gap as a function of pressure for different values of the Yukawa screening length. The black circles, red squares, and blue diamonds are the calculated band gaps for $\lambda \to \infty$, $\lambda =3$, and $\lambda =$ 2.5, respectively. The black line is a linear fit of the calculated GGA data.