Hysteresis in the Incommensurate Phase of the Spin-Peierls Compound CuGeO3: Electron Spin Resonance in High Field

The far-infrared electron spin resonance (ESR) technique is used to probe the incommensurate $I$ phase of the spin-Peierls compound CuGe${\mathrm{O}}_3$. At sufficiently low temperature, the ESR signal is seen to display hysteresis effects. Depending on the sweeping field direction, drastic changes are observed on both the linewidth and the resonance field $H_r$. From accurate determinations of $H_r$, the observed hysteresis is defined quantitatively. Observed on a large field range, this hysteretic behavior appears to be a new and basic property of the incommensurate $I$ phase.