| Popis: |
The magnetic susceptibility of three different as-grown NaCl:${\mathrm{Mn}}^{2+}$ crystals containing about 17 000, 900, and 200 ppm of ${\mathrm{Mn}}^{2+}$ has been studied in the 0.07--4.2-K temperature range in order to investigate the magnetic properties of the Suzuki-phase microcrystals. The present data demonstrate that the Suzuki-phase precipitates ${\mathrm{Na}}_{6}$${\mathrm{MnCl}}_{8}$ formed inside the host lattice undergo an antiferromagnetic phase transition at ${T}_{N}$=0.3 K. Within the experimental uncertainty, the three samples have the same value of the paramagnetic Curie temperature ${\mathrm{FTHETA}}_{S}$=1.5\ifmmode\pm\else\textpm\fi{}0.2 K. On the other hand, the results for T\ensuremath{\le}0.2 K point out the existence of loose spins, corresponding to ${\mathrm{Mn}}^{2+}$ ions in which the internal field is smaller than that for normal ${\mathrm{Mn}}^{2+}$ ions in the bulk Suzuki phase. The ratio between the concentration of loose spins and that of normal ${\mathrm{Mn}}^{2+}$ ions in the bulk Suzuki phase increases when dopant concentration decreases, while the average internal field acting on the loose spins increases upon increasing dopant concentration. This phenomenon is tentatively associated with size effects, the loose spins corresponding to ${\mathrm{Mn}}^{2+}$ ions lying on (or near to) the surface of the precipitate. Finally, for the less doped sample it is shown that 20% of ${\mathrm{Mn}}^{2+}$ ions are dissolved in the NaCl host lattice while the remainder form the Suzuki phase. |
