Spin-Peierls and Antiferromagnetic Phases in Cu1-xZnxGeO3: A Neutron Scattering Study

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Comprehensive neutron scattering studies were carried out on a series of high-quality single crystals of Cu₁₋ₓZnₓGeO₃. The Zn concentration, x, was determined for each sample using Electron Probe Micro-Analysis. The measured Zn concentrations were found to be 40-80% lower than the nominal values. Nevertheless the measured concentrations cover a wide range which enables a systematic study of the effects due to Zn-doping. We have confirmed the coexistence of spin-Peierls (SP) and antiferromagnetic (AF) orderings at low temperatures and the measured phase diagram is presented. Most surprisingly, long-range AF ordering occurs even in the lowest available Zn concentration, x=0.42%, which places important constraints on theoretical models of the AF-SP coexistence. Magnetic excitations are also examined in detail. The AF excitations are sharp at low energies and show no considerable broadening as x increases indicating that the AF ordering remains long ranged for x up to 4.7%. On the other hand, the SP phase exhibits increasing disorder as x increases, as shown from the broadening of the SP excitations as well as the dimer reflection peaks.