The Effect of Spin-Peierls Instability Suppression in Nanometer-Scale-Sized CuGeO3 Crystals

Charge and Bonding in CuGeO3 Nanorods

“…18,36−40 The recent development of a suite of CuGeO 3 nanorods of different lengths 13 (Figure 1b−d) offers the opportunity to unravel size effects on the dynamic properties and at the same time explore how and why the spin-Peierls transition is suppressed below a critical size (d crit ≈ 450 nm). 13,14 Electron spin resonance reveals no sign of an antiferromagnetic state at small sizes, 14 contrary to expectations based upon chemical substitution with Si, Zn, and Mg. 41−43 Instead, disorder emanating from the small surface layer and local changes in the Cu−O−Cu superexchange pathway that increase interchain interactions may place CuGeO 3 nanorods in the vicinity of a disorder-driven quantum critical point. 14 In this work, we reach beyond temperature, magnetic field, and pressure tuning techniques to explore the vibrational properties of CuGeO 3 nanorods as a function of size.…”

“…13,14 Electron spin resonance reveals no sign of an antiferromagnetic state at small sizes, 14 contrary to expectations based upon chemical substitution with Si, Zn, and Mg. 41−43 Instead, disorder emanating from the small surface layer and local changes in the Cu−O−Cu superexchange pathway that increase interchain interactions may place CuGeO 3 nanorods in the vicinity of a disorder-driven quantum critical point. 14 In this work, we reach beyond temperature, magnetic field, and pressure tuning techniques to explore the vibrational properties of CuGeO 3 nanorods as a function of size. An additional and rather novel aspect of our approach is that while all nanorod diameters are similar, the growth habit is such that length can be controlled to vary confinement in the c direction (Figures 1b−d).…”

“…This indicates a lattice that is stiffer and more difficult to dimerize, consistent with the suppression of the spin-Peierls transition at small sizes. 13,14 Taken together, these findings advance the understanding of size-driven phase transitions in nanoscale transition metal oxides and place these materials on a firm foundation for future work in high magnetic field. Phonon size effects may also be important for catalysis, thermal conductivity, and sensing applications.…”

“…The development of the superparamagnetic state in CoFe 2 O 4 and MgFe 2 O 4 nanoparticles is another illustration of how size allows access to completely different properties and areas of phase space. , Other examples include the spin-flop transition in α-Fe 2 O 3 that is suppressed below approximately 8 nm , and magnetoelectric coupling in Fe 3 O 4 , which is reduced with decreasing size . The discovery of size-induced quenching of the spin-Peierls transition in nanoscale CuGeO 3 , is another case where collective phenomena are suppressed by length scale effects. That the spin-Peierls state can be switched with both temperature and size is intriguing and merits additional mechanistic investigation.…”

“…CuGeO 3 is well-known as the first inorganic spin-Peierls material and, as such, is a superb platform for exploring temperature, − magnetic field, − pressure, − and doping effects. − This system consists of edge-sharing CuO 6 octahedra that form quasi-one-dimensional chains along the crystallographic c -axis (Figure a). , The Cu centers are d 9 and therefore S = 1/2. The Cu atoms dimerize below the T SP = 14 K spin-Peierls transition, and spin gaps open because singlets are formed. , Vibrational spectroscopies reveal the coupled phonons. ,− The recent development of a suite of CuGeO 3 nanorods of different lengths (Figure b–d) offers the opportunity to unravel size effects on the dynamic properties and at the same time explore how and why the spin-Peierls transition is suppressed below a critical size ( d crit ≈ 450 nm). , Electron spin resonance reveals no sign of an antiferromagnetic state at small sizes, contrary to expectations based upon chemical substitution with Si, Zn, and Mg. − Instead, disorder emanating from the small surface layer and local changes in the Cu–O–Cu superexchange pathway that increase interchain interactions may place CuGeO 3 nanorods in the vicinity of a disorder-driven quantum critical point …”