Properties of the spin systems of the localized 3d Mn²⁺ ions and the conduction π electrons in quasi-two-dimensional organic conductor κ-(BETS)₂Mn[N(CN)₂]₃ were accessed using ¹H and ¹³C NMR in order to find their relation to the metal-insulator transition which occurs at ∼23 K. The transition of the system into the insulating state is shown to be followed by localization of the π spins into a long-range ordered staggered structure of AF type. In contrast, the 3d Mn²⁺ electron spin moments form a disordered tilted structure, which may signify their trend to AF order, frustrated geometrically by the triangular arrangement of Mn in the anion layer. This result suggests that the MI transition in κ-(BETS)₂Mn[N(CN)₂]₃ is not the consequence of the interactions within the Mn²⁺ spins but due to the interactions within the π-electron system itself. Vice versa, it is more likelythat the disordered tilted structure of the Mn²⁺ spins is induced by the ordered π-spins via the π-d interaction.

The magnetic properties of the conduction π-electron system of κ-(BETS)₂Mn[N(CN)₂]₃ have been probed using ¹³C NMR. At ambient pressure, the metal-insulator transition observed in the resistivity measurements below T ≃ 23 K is shown to be accompanied by ordering of the π-spins in a long-range staggered structure. As the metal-insulator transition is suppressed by applying a small pressure of ∼0.5 kbar, the π-spin system maintains the properties of the metallic state down to 5 K.

In the organic charge transfer salt $\kappa$-(BETS)${}_2\mathrm{Mn}{\left[\mathrm{N}{\left(\mathrm{CN}\right)}_2\right]}_3$ the metallic conductivity is provided by itinerant $\pi$ electrons in the layers of BETS molecules, whereas magnetization is largely dominated by the localized $d$ electrons of the ${\mathrm{Mn}}^{2+}$ ions in the insulating anionic layers. We study magnetic properties of the compound in its low-temperature, Mott-insulating state by means of magnetic torque technique. The complex behavior of the torque can be consistently explained by the coexistence of two weakly interacting magnetic subsystems associated with paramagnetic $d$-electron spins and antiferromagnetically ordered $\pi$-electron spins, respectively. Based on the experimental data, we determine the principal axes of magnetization of the ${\mathrm{Mn}}^{2+}$ sublattice and propose a qualitative model for the $\pi$-electron spin arrangement, implying an important role of the Dzyaloshinskii-Moriya interaction.

Magnetic properties of the organic conductor κ-(BETS)₂Mn[N(CN)₂]₃ above and below the temperature of the metal-insulator transition that occurs at T _MI ≈ 25 K are studied by ¹H NMR. The proton spectrum is shown to be determined by the static dipolar fields from Mn²⁺ localized moments, while the ¹H spin-lattice relaxation is dominated by fluctuating fields from Mn²⁺ electrons. The NMR data, both static (the spectra) and dynamic (the spin-lattice relaxation), indicate the freezing of Mn²⁺ moments into a short-range or an incommensurate long-range antiferromagnetic order below T _MI.

Studies of dodecaboride LuB₁₂ in the temperature range of 10–300 K show that the ¹⁷⁵Lu spectrum is broadened due to the scatter of quadrupole frequency shifts caused by the defects in the Lu sublattice. To explain the discovered hysteresis in the temperature dependence of the ¹⁷⁵Lu linewidth, a scenario of “crystallization of structural defects” is proposed, in which the defects of the Lu sublattice, disordered at room temperature, are transformed into a more symmetrical and stable configuration with decreasing temperature, apparently due to static distortions of the boron frame caused by the cooperative Jahn–Teller effect.