Structure-induced ferromagnetic stabilization in free-standing hexagonal Fe(1.3)Ge nanowires.

Single-crystalline free-standing hexagonal Fe(1.3)Ge nanowires (NWs) are synthesized for the first time using a chemical vapor transport process without using any catalyst. Interestingly, Fe(1.3)Ge NWs are found to be ferromagnetic at room temperature, while bulk Fe(1.3)Ge has the lower critical temperature of 200 K. We perform first-principles density functional calculations and suggest that the observed strong ferromagnetism is attributed to the reduced distances between Fe atoms, increased number of Fe-Fe bonds, and the enhanced Fe magnetic moments. Both experimental and theoretical studies show that the magnetic moments are enhanced in the NWs, as compared to bulk Fe(1.3)Ge. We also modulate the composition ratio of as-grown iron germanide NWs by adjusting experimental conditions. It is shown that uniaxial strain on the hexagonal plane also enhances the ferromagnetic stability.