Site Selective Substitution and Charge Differentiation Around Ge Atom in FeGa3−xGex Proved by Ga-NQR with Super-cell Calculation

In order to obtain the local charge disturbance around substituted Ge atom in a prototype system of ferromagnetic quantum criticality, FeGa3−xGex, we have measured 69,71Ga Nuclear Quadrupole Resonance (NQR) spectra for single crystals. We have observed the characteristic NQR spectra in the x = 0.13 crystal, reflecting the locally differentiated electronic environments due to the Ge substitution. The observed spectra are compared with the simulated spectra based on the density functional theory-based supercell calculation of the NQR frequencies for individual Ga sites around the substituted Ge atom. From this we have argued that 1) the doped electrons by the Ge substitution are not distributed uniformly but confined within 3–4 Å range from the Ge atom, and the electron density is differentiated among Ga sites near the Ge atom, and 2) the Ge atom is preferentially substituted for Ga1 sites.