Unusual magnetization and Hall effect in the spinel chalcogenide (Fe$_{0.5}$Cu$_{0.5}$)Cr$_2$S$_4$*

We have measured the magnetization M and Hall resistivity $\rho_{xy}$ in single-crystal (Fe$_{0.5}$Cu$_{0.5}$)Cr$_2$S$_4$, a spinel chalcogenide compound. At the ferromagnetic transition (T$_c$ $\sim$ 280 K), M at weak field (at 100 gauss) displays an unusually abrupt onset vs. temperature T. Below $\sim$120 K, we observe the appearance of a second contribution to the magnetization, which appears as a kink in the field dependence of both $\rho_{xy}$ and M, characterized by a linearly rising segment and a final saturation in high field. We will discuss how these features relate to a possible second ordering arising from the two different sublattices (Fe,Cu) and Cr.