Magnetism in Co${}_{1-\mathrm{x}}$Fe${}_{\mathrm{x}}$Sb${}_3$ skutterudites from density functional theory

We have investigated the electronic and magnetic properties of Co${1-{\rm x}}$Fe${\rm x}$Sb${3}$ skutterudites from density functional theory and Monte Carlo simulations. We find that above a certain threshold in the Fe concentration, somewhere between x=0.125 and x=0.25, Co${}_{1-\mathrm{x}}$Fe${\rm x}$Sb$_{3}$ is ferromagnetic with an atomic moment which increases asymptotically towards about 1 ${\mu }_B$/Fe and a non-zero Curie temperature which reaches 70 K for FeSb${}_3$. Ferromagnetism is favored due to a Stoner instability in the electronic structure, where a large density of states at the Fermi-level makes it favorable to form the ferromagnetic ground state.