Magnetism of Al${}_x$Fe${}_{2-x}$GeO${}_5$ with Andalusite Structure

The magnetism of Al${}_x$Fe${}_{2-x}$GeO${}_5$ from $x$ = 0.09 to $x$ = 0.91 with andalusite structure was examined. The magnetic properties of Al${}_x$Fe${}_{2-x}$GeO${}_5$ at low temperatures were found to be weak ferromagnetic-like state for $x$ $<$ 0.3 and spin-glass state for $x$ $>$ 0.3. The small spontaneous magnetization that appears in the weak ferromagnetic-like phase would be due to the presence of Dzyaloshinsky-Moriya interaction or to the difference in the magnitude of the magnetic moment of Fe${}^{3+}$ in the octahedral and trigonal bipyramidal sites. The appearance of the spin-glass phase indicates that the dilution of Fe ions by Al ions in Al${}_x$Fe${}_{2-x}$GeO${}_5$ causes the competition between ferromagnetic and antiferromagnetic interactions. The $x$ dependence of the site occupancy of Fe ions suggests that Fe${}_2$GeO${}_5$ with andalusite structure cannot be synthesized.