Observation of the spin-Peierls transition in linear ${\mathrm{Cu}}^{2+}$ (spin-1/2) chains in an inorganic compound ${\mathrm{CuGeO}}_3$

The magnetic susceptibility of single-crystal ${\mathrm{CuGeO}}_3$, a linear ${\mathrm{Cu}}^{2+}$ (spin-1/2) chain compound, was measured. The susceptibilities in all the directions rapidly drop to small constant values with decreasing temperature below a phase transition temperature near 14 K. The magnetic-field dependence of the transition temperature quantitatively agrees with both theoretical predictions and experimental results for organic spin-Peierls systems. This Letter is the first report of an unambiguous determination of the existence of the spin-Peierls transition in an inorganic compound.