  We present the theoretical design of quantum dot (QD) artificial
ferromagnetic crystals. The electronic structure calculations based on local
spin density approximation (LSDA) show that our designed QD artificial crystal
from a structure comprising the crossing 0.104-micrometer-wide InAs quantum
wires (an effective Kagome lattice) has flat band characteristics. Our examined
QD artificial crystal has the ferromagnetic ground state when the flat band is
half-filled, even though it contains no magnetic elements. The ferromagnetic
and the paramagnetic state can be freely switched by changing the electron
filling via a gate voltage.
