Evolution of magnetic interactions in a pressure-induced Jahn-Teller driven magnetic dimensionality switch

Ghannadzadeh, Saman; Möller, J. S.; Goddard, Paul; Lancaster, Tom; Fan, Xing; Blundell, Stephen J.; Maisuradze, A.; Khasanov, R.; Manson, Jamie L.; Tozer, S. W.; Graf, David; Schlueter, John A.

doi:10.1103/physrevb.87.241102

Cited by 36 publications

(49 citation statements)

References 21 publications

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“…In addition, the method can be applied in bulky sample environments such as pressure cells [24,25]. In our experiments, we used powdered solution-grown PHCC polycrystalline samples of typical mass 800 mg.…”

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confidence: 99%

Pressure-Induced Quantum Critical and Multicritical Points in a Frustrated Spin Liquid

et al. 2014

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The quantum spin-liquid compound (C4H12N2)Cu2Cl6 is studied by µSR under hydrostatic pressures up to 23.6 kbar. At low temperatures, pressure-induced incommensurate magnetic order is detected beyond a quantum critical point at Pc ∼ 4.3 kbar. An additional phase transition to a different ordered phase is observed at P1 ∼ 13.4 kbar. The data indicate that the high-pressure phase may be a commensurate one. The established (P −T ) phase diagram reveals the corresponding pressure-induced multicritical point at P1, T1 = 2.0 K.Traditionally, magnetic insulators have been the most important prototype systems for testing concepts and theories of phase transitions, universality and scaling [1,2]. They owe this to their well-defined short-range interactions, a broad range of interaction topologies and dimensionalities, and their amenability to numerical modeling. With a more recent interest in quantum phase transitions [3,4], magnetic insulators have become the prototypes of choice to study quantum critical points (QCPs). Realizations of such important QCPs as BoseEinstein condensation (BEC) [5], deconfinement in one dimension [6,7], and the Ising model in a transverse field [8] have been found in quantum magnets in applied magnetic fields. Magnetic BEC, for example, occurs in gapped quantum antiferromagnets (AFMs) with a spin singlet ground state, when an external field drives the energy gap to zero by virtue of Zeeman effect. The result in spontaneous long-range magnetic order in the perpendicular direction, and thus a breaking of SO(2) symmetry [5]. At the QCP, the soft mode has a parabolic dispersion, so that the dynamical critical exponent is z = 2. By now, this transition has been extensively studied experimentally and theoretically [5].A qualitatively different type of soft mode transition in gapped quantum AFMs may occur if the spin gap is driven to zero by varying the ratio of exchange constants. The resulting spontaneous long-range magnetic order breaks SO(3) symmetry, and the spectrum is expected to be linear at the QCP (z = 1). In practice, the only way to continuously tweak the exchange interactions is by applying external pressure. Closing the spin gap with pressure in quantum Heisenberg AFMs has been attempted in experiments [9][10][11]. However, only one good realization of pressure-induced ordering in such systems has been found to date, namely, that in TlCuCl 3 [12][13][14]. Further studies of this QCP brought fascinating new insights [15], particularly the observation of a longitudinal mode, which is a magnetic analog of the celebrated Higgs boson [4]. In the present work, we report the observation of pressure-induced ordering in the S = 1/2 frustrated gapped quantum AFM (C 4 H 12 N 2 )Cu 2 Cl 6 (abbreviated PHCC), and use muon spin rotation (µSR) experiments to map out the P − T phase diagram. We show that the pressure-driven transition leads to an incommensurate magnetic order. At still higher pressures, we detect an additional transition and multicritical point. The indication is that these are an inc...

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Pressure-Induced Quantum Critical and Multicritical Points in a Frustrated Spin Liquid

et al. 2014

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“…8 Quantum magnets built from organic molecules can be very susceptible to perturbation by external pressure due to their 'soft' molecular frameworks. 9 This paper is concerned with the S = 1/2 quasi-two-dimensional gapped quantum antiferromagnet piperazinium hexachlorodicuprate [(C 4 H 12 N 2 )Cu 2 Cl 6 , hereafter PHCC]. PHCC crystallizes in the triclinic space group P1 with lattice parameters 10 a = 7.984(4)Å, b = 7.054(4)Å, c = 6.104(3)Å, α = 111.23 (8) • , β = 99.95 (9) • , γ = 81.26 (7) • .…”

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confidence: 99%

“…9 This paper is concerned with the S = 1/2 quasi-two-dimensional gapped quantum antiferromagnet piperazinium hexachlorodicuprate [(C 4 H 12 N 2 )Cu 2 Cl 6 , hereafter PHCC]. PHCC crystallizes in the triclinic space group P1 with lattice parameters 10 a = 7.984(4)Å, b = 7.054(4)Å, c = 6.104(3)Å, α = 111.23 (8) • , β = 99.95 (9) • , γ = 81.26 (7) • . The spin-1/2 Cu 2+ ions are connected by a complex layered network (see Fig.…”

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confidence: 99%

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

et al. 2015

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We present inelastic neutron scattering experiments on the S = 1/2 frustrated gapped quantum magnet piperazinium hexachlorodicuprate (PHCC) under applied hydrostatic pressure. These results show that at 9 kbar the magnetic triplet excitations in the system are gapless, contrary to what was previously reported. Our results are in agreement with recent muon-spin relaxation experiments which found magnetic order above a quantum-critical point at 4.3 kbar. We show that the changes in the excitation spectrum can be primarily attributed to the change in a single exchange pathway.

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“…An added advantage of molecular systems is the ability to make controlled adjustments to the crystal structure, thereby tuning interaction strengths and better testing the predictions of the SLHAFM and associated models. To this end, we and others have previously shown that it is possible to gain a degree of control over the primary exchange energy in low-dimensional molecular antiferromagnets via constitutional changes that include deuteration 18 , anion substitution 11,19 , exchange of halide ligands 20,21 , and the application of high pressures 22,23 .…”

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confidence: 99%

Control of the third dimension in copper-based square-lattice antiferromagnets

et al. 2016

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Using a mixed-ligand synthetic scheme, we create a family of quasi-two-dimensional antiferromagnets, namely, [Cu(HF2)(pyz)2]ClO4 [pyz = pyrazine], [CuL2(pyz)2](ClO4)2 [L = pyO = pyridine-N-oxide and 4-phpyO = 4-phenylpyridine-N-oxide. These materials are shown to possess equivalent two-dimensional [Cu(pyz)2] 2+ nearly square layers, but exhibit interlayer spacings that vary from 6.5713Å to 16.777Å, as dictated by the axial ligands. We present the structural and magnetic properties of this family as determined via x-ray diffraction, electron-spin resonance, pulsed-and quasistatic-field magnetometry and muon-spin rotation, and compare them to those of the prototypical two-dimensional magnetic polymer Cu(pyz)2(ClO4)2. We find that, within the limits of the experimental error, the two-dimensional, intralayer exchange coupling in our family of materials remains largely unaffected by the axial ligand substitution, while the observed magnetic ordering temperature (1.91 K for the material with the HF2 axial ligand, 1.70 K for the pyO and 1.63 K for the 4-phpyO) decreases slowly with increasing layer separation. Despite the structural motifs common to this family and Cu(pyz)2(ClO4)2, the latter has significantly stronger two-dimensional exchange interactions and hence a higher ordering temperature. We discuss these results, as well as the mechanisms that might drive the long-range order in these materials, in terms of departures from the ideal S = 1/2 two-dimensional square-lattice Heisenberg antiferromagnet. In particular, we find that both spin exchange anisotropy in the intralayer interaction and interlayer couplings (exchange, dipolar, or both) are needed to account for the observed ordering temperatures, with the intralayer anisotropy becoming more important as the layers are pulled further apart.

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Evolution of magnetic interactions in a pressure-induced Jahn-Teller driven magnetic dimensionality switch

Cited by 36 publications

References 21 publications

Pressure-Induced Quantum Critical and Multicritical Points in a Frustrated Spin Liquid

Pressure-Induced Quantum Critical and Multicritical Points in a Frustrated Spin Liquid

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

Control of the third dimension in copper-based square-lattice antiferromagnets

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