  Nanomagnets with giant magnetic anisotropy energy and long coherence time are
desired for various technological innovations such as quantum information
procession and storage. Based on the first-principles calculations and model
analyses, we demonstrate that a single uranium atom substituting Al on the
Al2O3(0001) surface may have high structural stability and large magnetic
anisotropy energy up to 48 meV per uranium atom. As the magnetization resides
in the localized f-shell and is not much involved in chemical bonding with
neighbors, long coherence time up to ~1.6 mS can be achieved for the quantum
spin states. These results suggest a new strategy for the search of ultrasmall
magnetic units for diverse applications in the quantum information era.
