Magnetic properties of Na-K clusters in low-silica X zeolite doped by pressure loading

Low-silica X (LSX) zeolite has the FAU-type framework structure constructed of supercages and β-cages with effective inside diameters of 13 and 7 Å, respectively. Respective cages are arrayed in a diamond structure. Na-K clusters are formed by the loading of guest potassium atoms nK into LSX, where the unloaded LSX has 4Na and 8K zeolite-cations per supercage (or β-cage) as given by Na₄K₈Al₁₂Si₁₂O ₄₈. N-type ferrimagnetism has been observed at ambient loading densities of K atoms, 6.5 < n < 8.5. Ferrimagnetism was not observed at the maximum loading density at ambient pressure, n ≈ 9. In the present study, we extended the loading density for 9 < n by the pressure-loading technique. Spontaneous magnetization is observed again below 10.5 and 9.1 K at the loading pressures ≈ 400 and ≈ 520 MPa, respectively. Respective Weiss temperatures are -23 and -32 K. These results indicate that the ferrimagnetism appears again at higher loading densities.