The search for magnetic analogues of superconducting compounds has lead to
the discovery of compounds with giant magnetoresistance. For example, a col
ossal negative magnetoresistance of up to 20 % at 180 K has been measured f
or the chalcospinel Fe0.5Cu0.5Cr2S4. Here spin-polarized ab-initio band str
ucture calculations are performed on the title compound in order to gain an
understanding of its electronic and magnetic behavior, the structural info
rmation for these calculations being obtained from neutron diffraction data
. The valency of iron is also investigated by temperature-dependent Mossbau
er spectroscopy.