Spin-Peierls and antiferromagnetic phases in Cu1−xZnxGeO

Michael Martin

¹

,

Masashi Hase

²

,

K. Hirota

³

et al.

Abstract

Comprehensive neutron scattering studies were carried out on a series of high-quality single crystals of Cu 1−x Zn x GeO 3 . 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

Dopant-bound spinons in Cu 1 − x Zn x GeO 3

“…We expect that the appearance of antiferromagnetic order, while the dimerization persists (see, e.g., the shoulder close to the laser line for x = 3.3% in Fig. 1), can be understood as an ordering of these S = 1/2 states due to their interaction [7,27]. But this question is far from being settled.…”

“…2% Zn-doping, a coexistence of SP and Néel phase is observed. Recent investigations indicated a coexistence of both phases for a broad interval of dopings [6,7,8].…”

Dynamics of weakly coupled random antiferromagnetic quantum spin chains

“…Thus our results allow for a detailed quantitative comparison with future experiments. A few years earlier, Martin et al studied the excitation spectrum of doped CuGeO 3 using inelastic neutron scattering, 17 and found sharp propagating spin-wave excitations when the system is Néel ordered, despite the fact that the Néel phase is stabilized by disorder. They found the spinwave spectrum to be linear.…”

“…Amazingly, when doping reaches certain levels the spins become Néel ordered at low temperature, which has been observed experimentally in Zn-and Si-doped CuGeO 3 . [11][12][13][14][15][16][17][18][19][20] Since these experimental discoveries a number of theoretical papers have addressed the static Néel ordering in these systems [24][25][26][27][28][29][30][31][32][33][34][35][36] using meanfield theory. On the other hand the collective excitations and dynamical response functions which have been studied experimentally using inelastic neutron scattering, 20 have not been studied theoretically thus far.…”

Unconventional antiferromagnetic correlations of the doped Haldane gapsystem Y 2 BaNi 1 - x Zn x O 5

“…For instance, it is possible to substitute a small fraction of the Cu sites (being a spin-1/2 ion) by Ni (being a spin-1 ion) [10] or Co (being a spin-3/2 ion) [11]. It is possible to substitute Cu by the non magnetic ions Zn [12][13][14] or Mg [15]. It is also possible to substitute some Ge sites (being outside the CuO 2 chains) with Si [16].…”