A complex study of magnetic properties including dc magnetization, ${}^1\mathrm{H}$ NMR, and magnetic torque measurements has been performed for the organic conductor $\kappa$-(BETS)${}_2$Mn[N(CN)${}_2$]${}_3$ which undergoes a metal-insulator transition at $T_{\mathrm{MI}}\approx 25$K. NMR and the magnetization data indicate a transition in the manganese subsystem from paramagnetic to a frozen state at $T_{\mathrm{MI}}$, which is, however, not a simple Néel type order. Further, a magnetic field induced transition resembling a spin flop has been detected in the torque measurements at temperatures below $T_{\mathrm{MI}}$. This transition is most likely related to the spins of $\pi$ electrons localized on the organic molecules BETS and coupled with the manganese $3d$ spins via exchange interaction.

• Received 25 November 2010

DOI:https://doi.org/10.1103/PhysRevB.83.094425