  In zeolite low-silica X (LSX), beta-cages with the inside diameter of approx
7 AA{} are arrayed in a diamond structure. Among them, supercages with the
inside diameter of approx 13 AA{} are formed and arrayed in a diamond structure
by the sharing of windows with the inside diameter of approx 8 AA{}. The
chemical formula of zeolite LSX used in the present study is given by
Na$_{x}$K$_{12-x}$Al$_{12}$Si$_{12}$O$_{48}$ per supercage (or beta-cage),
where Na$_{x}$K$_{12-x}$ and Al$_{12}$Si$_{12}$O$_{48}$ are the exchangeable
cations of zeolite LSX and the aluminosilicate framework, respectively. Na-K
alloy clusters are incorporated in these cages by the loading of guest K metal
at $n$K atoms per supercage (or beta-cage). A N'eel's N-type ferrimagnetism has
been observed at $n = 7.8$ for $x = 4$. In the present paper, optical, magnetic
and electrical properties are studied in detail mainly for $x = 4$.
Ferrimagnetic properties are observed at $6.5 < n < 8.5$. At the same time, the
Curie constant suddenly increases. An optical reflection band of beta-cage
clusters at 2.8 eV is observed at $n > 6.5$ in accordance with the sudden
increase in the Curie constant. An electrical resistivity indicates metallic
values at $n$ gtrapprox 6, because a metallic state is realized in the energy
band of supercage clusters. The ferrimagnetism is explained by the
antiferromagnetic interaction between the magnetic sublattice of itinerant
electron ferromagnetism at supercage clusters and that of localized moments at
beta-cage clusters. The electrical resistivity in ferrimagnetic samples at $n =
8.2$ for $x = 4$ increases extraordinarily at very low temperatures, such as
approx $10^6$ times larger than the value at higher temperatures. Observed
anomalies in the electrical resistivity resembles the Kondo insulator, but
itinerant electrons of narrow energy band of supercage clusters are
ferromagnetic.
