Title: Spin dynamics of FeGa$_{3-x}$Ge$_x$ studied by Electron Spin Resonance,
Abstract: The intermetallic semiconductor FeGa$_{3}$ acquires itinerant ferromagnetism
upon electron doping by a partial replacement of Ga with Ge. We studied the
electron spin resonance (ESR) of high-quality single crystals of
FeGa$_{3-x}$Ge$_x$ for $x$ from 0 up to 0.162 where ferromagnetic order is
observed. For $x = 0$ we observed a well-defined ESR signal, indicating the
presence of pre-formed magnetic moments in the semiconducting phase. Upon Ge
doping the occurrence of itinerant magnetism clearly affects the ESR properties
below $\approx 40$~K whereas at higher temperatures an ESR signal as seen in
FeGa$_{3}$ prevails independent on the Ge-content. The present results show
that the ESR of FeGa$_{3-x}$Ge$_x$ is an appropriate and direct tool to
investigate the evolution of 3d-based itinerant magnetism.