Magnetic Properties of Spinel FeCr${}_2$S${}_4$ in High Magnetic Field

We studied temperature and magnetic field dependence of magnetization, $M(T)$ and $M(B)$, on thiospinel FeCr${}_2$S${}_4$. We observed a step-like anomaly at $T_{OO}\sim$ 9 K for $M$($T$) attributed to an orbital order transition in magnetic field 0 $<B\le$ 7 T. Furthermore, also for $M$($B$), an step-like anomaly appears at $B_c\sim$ 5.5 T below $T_{OO}$. This suggests an existence of a magnetic phase boundary at $B_c$ in $T<T_{OO}$. Because the anomaly at $B_c$ of $M(B)$ exists in the orbital ordered phase, the spin structure of FeCr${}_2$S${}_4$ in $T<T_{OO}$ is strongly coupled with the lattice of the system.