Ferromagnetic Nanocrystals of Antiferromagnetic FeGe

Epitaxial nanocrystals of FeGe have been stabilized on Ge(111). The nanocrystals assume a quasi one-dimensional shape as they grow exclusively along the $<$1$\mathop 1\limits^- $0$>$ direction of the Ge(111) substrate, culminating in the monoclinic modification of FeGe. The uni-directional growth results from a close match between the Ge-atom spacing along $<$1\={ }10$>$Ge and monoclinic b-axis of FeGe. Whereas monoclinic FeGe is antiferromagnetic in the bulk, the nanocrystals are surpisingly strong ferromagnets below $\sim $200 K with an average magnetic moment of 0.8 $\mu _{B}$ per Fe atom. Density functional calculations demonstrate that volume ferromagnetism is stabilized predominantly by compressive strain normal to the growth direction of the nanocrystals.