Observation of a dimerized state in the S=1/2 quasi-one-dimensional antiferromagnet ${\mathrm{Sr}}_{14}$${\mathrm{Cu}}_{24}$${\mathrm{O}}_{41}$

We have performed magnetic susceptibility and electron spin resonance measurements on the quasi-one-dimensional magnet ${\mathrm{Sr}}_{14}$ ${\mathrm{Cu}}_{24}$ ${\mathrm{O}}_{41}$, which has simple chains and two-leg ladder chains of copper ions. The magnetic signals which we observed below room temperature mainly come from the simple chains. The experimental results show that the simple chain unexpectedly has a spin gap in the excitation spectrum, which originates from a dimerized state. © 1996 The American Physical Society.