Specific heat and susceptibility of the 1-dimensional Heisenberg antiferromagnet Cu(Pyrazine) (NO3)2. evidence for random exchange effects at low temperatures

Mennenga, G.; Jongh, L.J. de; Huiskamp, W.J.; Reedijk, Jan

doi:10.1016/0304-8853(84)90049-0

Cited by 41 publications

(23 citation statements)

References 38 publications

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“…Experimentally, such a linear-in-T term at H = 0 was found in Cu(pyrazine)(NO 3 ) 2 (CuPzN) 24 and copper benzoate 25 . For finite H, the thermodynamic Bethe ansatz was applied and confirmed experimentally in CuPzN (ref.…”

Section: Lettersmentioning

confidence: 84%

Quantum criticality among entangled spin chains

et al. 2017

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An important challenge in magnetism is the unambiguous identification of a quantum spin liquid 1,2 , of potential importance for quantum computing. In such a material, the magnetic spins should be fluctuating in the quantum regime, instead of frozen in a classical long-range-ordered state. While this requirement dictates systems 3,4 wherein classical order is suppressed by a frustrating lattice 5 , an ideal system would allow tuning of quantum fluctuations by an external parameter. Conventional three-dimensional antiferromagnets can be tuned through a quantum critical point-a region of highly fluctuating spins-by an applied magnetic field. Such systems suffer from a weak specific-heat peak at the quantum critical point, with little entropy available for quantum fluctuations 6 . Here we study a different type of antiferromagnet, comprised of weakly coupled antiferromagnetic spin-1/2 chains as realized in the molecular salt K 2 PbCu(NO 2 ) 6 . Across the temperature-magnetic field boundary between three-dimensional order and the paramagnetic phase, the specific heat exhibits a large peak whose magnitude approaches a value suggestive of the spinon Sommerfeld coefficient of isolated quantum spin chains. These results demonstrate an alternative approach for producing quantum matter via a magnetic-field-induced shift of entropy from one-dimensional short-range order to a three-dimensional quantum critical point.Previous work on field-tuning of quantum fluctuations has focused on the transverse-field Ising model where the magnetic field (H) couples to a sector of the Hamiltonian not directly modifying the order parameter. While this paradigm has been explored in the three-dimensional (3D) dipolar ferromagnet LiHoF 4 (refs 7,8 ), and the 1D system CoNb 2 O 6 (ref. ), the need for a unique Ising-axis normal restricts the number of potential quantum-spin-liquid host materials. For the much broader class of 3D antiferromagnets (AFs), H can indeed tune the Néel temperature (T N ) into the quantum regime. Within the ordered state, however, on increasing H from zero one first encounters a spin-flop transition (for finite spin anisotropy), followed by a gradual reorientation of those spins (Fig. 1a). Hence, in destroying Néel order, H decreases the transverse components of the staggered moment to a value that is vanishingly small near the transition to the field-polarized state, leaving little entropy to be lost near T = 0, and thus low spectral weight available for quantum entanglement 6 . Here we demonstrate a different approach to tuning through a quantum critical point (QCP). The quasi-1D spin-1/2 AF K 2 PbCu(NO 2 ) 6 orders classically at 0.68 K (ref. 10; Fig. 1b). At lower temperatures within the Néel state, applied H values less than the intra-chain mean field cause little change in the specific heat C(T, H). At the phase boundary, however, a large amount of entropy is released, leading to a peak in C/T (Fig. 1c), the value of which (~ 2 J mol -1 K -2 at the lowest temperatures studied) is suggestive of the spinon ...

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Section: Lettersmentioning

confidence: 84%

Quantum criticality among entangled spin chains

et al. 2017

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“…Cu(pyz)(NO 3 ) 2 has been chosen because it provides a good experimental realisation of the S = 1/2 1D antiferromagnetic Heisenberg model [14,15]. As a result, its magnetic [11,[14][15][16][17][18], spin-dynamic [19][20][21][22][23][24], thermal [25,26], and vibrational [27,28] properties have been the subject of experimental and theoretical investigation. Cu(pyz)(NO 3 ) 2 in a coordination polymer consisting of a crystalline arrangement of chains of Cu 2+ ions linked by pyrazine (pyz) ligands parallel to the a axis of its unit cell, where each Cu 2+ ion is also bonded to a pair of nitrate ions, illustrated in Fig.…”

Section: Introductionmentioning

confidence: 99%

Exchange constants in molecule-based magnets derived from density functional methods

2017

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Cu(pyz)(NO3)2 is a quasi one-dimensional molecular antiferromagnet that exhibits three dimensional long-range magnetic order below TN = 110 mK due to the presence of weak inter-chain exchange couplings. Here we compare calculations of the three largest exchange coupling constants in this system using two techniques based on plane-wave basis-set density functional theory: (i) a dimer fragment approach and (ii) an approach using periodic boundary conditions. The calculated values of the large intrachain coupling constant are found to be consistent with experiment, showing the expected level of variation between different techniques and implementations. However, the interchain coupling constants are found to be smaller than the current limits on the resolution of the calculations. This is due to the computational limitations on convergence of absolute energy differences with respect to basis set, which are larger than the inter-chain couplings themselves. Our results imply that errors resulting from such limitations are inherent in the evaluation of small exchange constants in systems of this sort, and that many previously reported results should therefore be treated with caution.

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“…Experimental information on s B is, however, missing because most of the known realizations of the Hamiltonian (1) have large values of the intrachain exchange constant J=k B 100-1000 K, that severely limits the region of the phase diagram accessible using standard laboratory equipment. The existing results are limited to studies of the phonon thermal conductivity ph B; T in CuGeO 3 and Yb 4 As 3 [9][10][11][12], and do not address the behavior of s B; T. Copper pyrazine dinitrate CuC 4 H 4 N 2 NO 3 2 (CuPzN) appears to be an ideal compound for the thermal conductivity experiments in magnetic field, as J=k B 10:3 K [13,14] and therefore B c 15:0 T, which is easily accessible experimentally. CuPzN has an orthorhombic structure with lattice constants a 6:712 A, b 5:142 A, and c 11:73…”

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confidence: 99%

Magnetothermal Transport in the Spin-12Chains of Copper Pyrazine Dinitrate

et al. 2007

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We present experiments on the thermal transport in the spin-1/2 chain compound copper pyrazine dinitrate Cu(C4H4N2)(NO3)2. The heat conductivity shows a surprisingly strong dependence on the applied magnetic field B, characterized at low temperatures by two main features. The first one appearing at low B is a characteristic dip located at muBB approximately kBT, that may arise from umklapp scattering. The second one is a plateaulike feature in the quantum critical regime, muB|B - Bc| < kBT, where Bc is the saturation field at T=0. The latter feature clearly points towards a momentum and field-independent mean free path of the spin excitations, contrary to theoretical expectations.

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Specific heat and susceptibility of the 1-dimensional Heisenberg antiferromagnet Cu(Pyrazine) (NO3)2. evidence for random exchange effects at low temperatures

Cited by 41 publications

References 38 publications

Quantum criticality among entangled spin chains

Quantum criticality among entangled spin chains

Exchange constants in molecule-based magnets derived from density functional methods

Magnetothermal Transport in the Spin-12Chains of Copper Pyrazine Dinitrate

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