Frustration-induced two-dimensional quantum disordered phase in piperazinium hexachlorodicuprate

Abstract

Piperazinium hexachlorodicuprate is shown to be a frustrated quasi-two-dimensional quantum Heisenberg antiferromagnet with a gapped spectrum. Zero-field inelastic neutron scattering and susceptibility and specificheat measurements as a function of applied magnetic field are presented. At Tϭ1.5 K, the magnetic excitation spectrum is dominated by a single propagating mode with a gap, ⌬ϭ1 meV, and bandwidth of Ϸ1.8 meV in the (h0l) plane. The mode has no dispersion along the b* direction indicating that neighboring a-c planes of the triclinic structure are magnetically decoupled. The heat capacity shows a reduction of the gap as a function of applied magnetic field in agreement with a singlet-triplet excitation spectrum. A field-induced ordered phase is observed in heat capacity and magnetic susceptibility measurements for magnetic fields greater than H c1 Ϸ7.5 T. Analysis of the neutron-scattering data reveals the important exchange interactions and indicates that some of these are highly frustrated.

Spin dynamics in pressure-induced magnetically ordered phases in(C4H12N2)Cu2Cl<

“…Our analysis closely follows that used by Stone et al in Ref. 10. To within experimental resolution, the scattering can in all cases be attributed to a single sharp magnon branch.…”

“…Overall, our results at ambient pressure are in good agreement with the values obtained previously without the complication of performing an experiment inside of a pressure cell. 10 Our main result is that at 9 kbar, the gap ∆ = 0.0(1) meV, i.e. the spectrum is gapless.…”

“…In our case, the sum included all those bonds as in the approach of Ref. 10. The corresponding labeling scheme is shown in Fig.…”

“…3 and in Ref. 10, happens to have the largest bond energy at ambient pressure. Furthermore, we note that we have not been able to observe a magnetic Bragg peak in the magnetically ordered phases which would be consistent with a small ordered moment size.…”

Crystals for neutron scattering studies of quantum magnetism

“…Recent breakthroughs were therefore achieved in studies of organic quantum magnets, particularly in transition metal complexes. Among these compounds, for neutron experiments, one finds excellent one-dimensional [10][11][12][13][14] and two-dimensional [15][16][17] spin networks with varying degrees of geometric frustration [15,18] and typical magnetic energy scales of 1 meV. These energies correspond to temperatures [19][20][21][22] and magnetic fields [23][24][25][26][27] that can be realized in neutron experiments.…”