  A detailed study of the electronic transport and magnetic properties of
Fe$_{1-x}$Cu$_x$Cr$_2$S$_4$ ($x \leq 0.5$) on single crystals is presented. The
resistivity is investigated for $2 \leq T \leq 300$ K in magnetic fields up to
14 Tesla and under hydrostatic pressure up to 16 kbar. In addition
magnetization and ferromagnetic resonance (FMR) measurements were performed.
FMR and magnetization data reveal a pronounced magnetic anisotropy, which
develops below the Curie temperature, $T_{\mathrm{C}}$, and increases strongly
towards lower temperatures. Increasing the Cu concentration reduces this
effect. At temperatures below 35 K the magnetoresistance, $MR = \frac{\rho(0) -
\rho(H)}{\rho(0)}$, exhibits a strong dependence on the direction of the
magnetic field, probably due to an enhanced anisotropy. Applying the field
along the hard axis leads to a change of sign and a strong increase of the
absolute value of the magnetoresistance. On the other hand the
magnetoresistance remains positive down to lower temperatures, exhibiting a
smeared out maximum with the magnetic field applied along the easy axis. The
results are discussed in the ionic picture using a triple-exchange model for
electron hopping as well as a half-metal utilizing a band picture.
