  We report on neutron diffraction, thermal expansion, magnetostriction,
dielectric, and specific heat measurements on polycrystalline FeCr2S4 in
external magnetic fields. The ferrimagnetic ordering temperatures
$T_{\mathrm{C}}\approx 170$ K and the transition at $T_{\mathrm{OO}}\approx 10$
K, which has been associated with orbital ordering, are only weakly shifted in
magnetic fields up to 9 T. The cubic lattice parameter is found to decrease
when entering the state below $T_{\mathrm{OO}}$. The magnetic moments of the
Cr- and Fe-ions are reduced from the spin-only values throughout the
magnetically ordered regime, but approach the spin-only values for fields
$>$5.5 T. Thermal expansion in magnetic fields and magnetostriction experiments
indicate a contraction of the sample below about 60 K. Below $T_{\mathrm{OO}}$
this contraction is followed by a moderate expansion of the sample for fields
larger than $\sim$4.5 T. The transition at $T_{\mathrm{OO}}$ is accompanied by
an anomaly in the dielectric constant. The dielectric constant depends on both
the strength and orientation of the external magnetic field with respect to the
applied electric field for $T<T_{\mathrm{OO}}$. A linear correlation of the
magnetic-field-induced change of the dielectric constant and the magnetic-field
dependent magnetization is observed. This behaviour is consistent with the
existence of a ferroelectric polarization and a multiferroic ground state below
10 K.

Strongly Correlated Electrons