Bulk electronic properties of $\mathrm{Fe}{\mathrm{Si}}_{1-x}{\mathrm{Ge}}_x$ investigated by high-resolution x-ray spectroscopies

We report an investigation of the bulk electronic properties of Fe in $\mathrm{Fe}{\mathrm{Si}}_{1-x}{\mathrm{Ge}}_x$ ($x=0$, 0.11, 0.19, and 0.44) measured by high-resolution x-ray absorption spectroscopy at the $\mathrm{Fe}K$ edge, $\mathrm{Fe}K\beta$ x-ray emission, and $1s3p$ resonant x-ray emission spectroscopies. The emission data clearly show an increase in the magnetic moment when $x$ increases from 0 to 0.44. This doping-induced spin transition is accompanied by the onset of the magnetic order at $x⩾0.2$. The $1s3p$ resonant x-ray emission data reveal that the $\mathrm{Fe}3d$ states exhibit a delocalized character, while no intermediate valence admixture takes place. This is at odd with the intermediate valence Kondo insulator model and rather supports the local density approximation band theory.

Figure 1

(Color online) Magnetic susceptibility $M∕H$ as a function of temperature for $\mathrm{Fe}{\mathrm{Si}}_{1-x}{\mathrm{Ge}}_x$ ($x=0$, 0.11, 0.19, and 0.44).

Figure 2

(Color online) Bottom: $\mathrm{Fe}K$ PFY-XAS spectra for $x=0$ $\left(16\mathrm{K}\right)$, 0.19 (50 and $300\mathrm{K}$), and 0.44 (50 and $300\mathrm{K}$) samples and Fe metal $\left(300\mathrm{K}\right)$. The intensity is normalized to the maximum. Top: Intensity difference with the $x=0$ spectrum.

Figure 3

(Color online) (a) Bottom: $\mathrm{Fe}K\beta$ emission spectra as a function of $x$ at $300\mathrm{K}$. Top: Intensity difference with the $x=0$ spectrum. (b) Same data as (a) with the $K\beta$ peaks adjusted in energy to that of $x=0$ and with the Fe metal spectrum. (c) $\mathrm{Fe}K\beta$ emission spectra at $17\mathrm{K}$. The peak positions of $\mathrm{Fe}K\beta$ are adjusted.

Figure 4

(Color online) Bottom: $\mathrm{Fe}K\beta$ emission spectra obtained at several temperatures between 17 and $300\mathrm{K}$ for (a) $x=0.19$ and (b) $x=0.44$. The peak positions are not adjusted. Top: Intensity difference between the low temperature spectra and the $300\mathrm{K}$ spectrum.

Figure 5

(Color online) (a) Center of mass (c.m.) and integrals of the absolute values of the difference (IAD) as a function of $x$. (b) Intensity ratio of $K{\beta }^{\prime }$ to $K{\beta }_{1,3}$ and $K{\beta }_{1,3}$ peak energy shift as a function of $x$ relative to $x=0$ at 17 and $300\mathrm{K}$.

Figure 6

(Color online) Resonant inelastic x-ray scattering of FeSi $(x=0)$ for $K\beta$ at $\mathrm{Fe}K$ absorption edge with the PFY spectrum at $16\mathrm{K}$.

Figure 7

(Color online) (a) Example of the curve fit for $K\beta$ emission of FeSi $(x=0)$ at the incident photon energy of $7112\mathrm{eV}$. (b) The intensities of fluorescence and Raman parts as a function of the incident photon energies at $16\mathrm{K}$ for the data in Fig. 6.