Transitions from a Kondo-like diamagnetic insulator into a modulated ferromagnetic metal in FeGaGe.

One initial and essential question of magnetism is whether the magnetic properties of a material are governed by localized moments or itinerant electrons. Here, we expose the case for the weakly ferromagnetic system FeGa Ge , wherein these two opposite models are reconciled, such that the magnetic susceptibility is quantitatively explained by taking into account the effects of spin-spin correlation. With the electron doping introduced by Ge substitution, the diamagnetic insulating parent compound FeGa becomes a paramagnetic metal as early as at y=0.01, and turns into a weakly ferromagnetic metal around the quantum critical point =0.15. Within the ferromagnetic regime of FeGa Ge , the magnetic properties are of a weakly itinerant ferromagnetic nature, located in the intermediate regime between the localized and the itinerant dominance. Our analysis implies a potential universality for all itinerant-electron ferromagnets.