New scenario for the decay of spin-Peierls state in CuGeO$_3$: Fe. Onset of a quantum critical point

It is found experimentally that the introduction of $1\%$ Fe in the CuGeO$_3$ matrix gives rise to a strong disorder in the magnetic subsystem and leads to an appearance of the $\chi \sim 1/T^\alpha $, ($\alpha \approx0.36$) low-temperature asymptotic form for magnetic susceptibility over a wide temperature range $1.7\leq T\leq30$ K. A model attributing this anomaly to the suppression of spin-Peierls state as a result of the formation of the quantum critical point is proposed.