Magnetically linear and quadratic hexanitrocuprates

Blöte, Henk W. J.

doi:10.1063/1.327183

Cited by 9 publications

(2 citation statements)

References 16 publications

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“…4 that copper usually suffers a Jahn-Teller distortion. Similarly, K2Pb[Cu(NO 2)6] is face-centered cubic at room temperature, which implies threedimensional magnetism, but it undergoes several structural phase transitions as it is cooled and it too acts as an antiferromagnetic linear chain [70]. This is because the distortions can become cooperative [68].…”

Section: Some Other Aspectsmentioning

confidence: 99%

Lower Dimensional Magnetism

Carlin¹

1986

Magnetochemistry

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Much of what has gone heretofore could come under the classification of short-range order. Certainly the intracluster magnetic exchange in Chap. 5 falls within this heading, and a significant part of the discussion of Chap. 6 also dealt with this subject. By "shortrange order," we shall mean the accumulation of entropy in a magnetic system above the long-range ordering temperature. Though this occurs with all magnetic systems, the physical meaning implied by the chapter title is that magnetic ions are assumed here to interact only with their nearest neighbors in a particular spatial sense. For operational purposes, the term will be restricted to magnetic interactions in one and two (lattice) dimensions. In that regard, it is interesting to note that the discussion is thereby restricted to the paramagnetic region. Let it be clear right at the beginning that this magnetic behavior follows directly from the structure of the various compounds.The study of magnetic systems which display large amounts of order in but one or two dimensions has been one of the most active areas recently in solid state physics and chemistry [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20]. The reason for this seems to be that, though Ising investigated the theory of ordering in a one-dimensional ferromagnet as long ago as 1925 [21], it was not until recently that it was realized that compounds existed that really displayed this short-ranged order. The first substance recognized as behaving as a linear chain or onedimensional magnet is apparently CU(NH3)4S0 4' H 20 (CTS). Broad maxima at low temperatures were discovered in measurements of both the susceptibilities and the specific heat [22]. Griffith [23] provided the first quantitative fit of the data, using the calculations for a linear chain of Bonner and Fisher [24]. Fortunately, the theoreticians had been busy already for some time [4] in investigating the properties of onedimensional systems, so that the field has grown explosively once it was recognized that experimental realizations could be found. One-Dimensional or Linear Chain SystemsThere are very good theories available which describe the thermodynamic properties of one-dimensional (lD) magnetic systems, at least for 9'=t; what may be more surprising is that there are extensive experimental data as well of metal ions linked into uniform chains.The first point ofinterest, discovered long ago by Ising [21], is that an infinitely long ID system undergoes long-range order only at the temperature of absolute zero.R. L. Carlin, Magnetochemistry

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Section: Some Other Aspectsmentioning

confidence: 99%

Lower Dimensional Magnetism

Carlin¹

1986

Magnetochemistry

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“…Previous C(T, H = 0) measurements on K 2 PbCu(NO 2 ) 6 show a single broad λ peak, signalling a transition to 3D order around T N ~ 0.50 K (ref. 10 ). Our elastic neutron scattering measurements down to T = 0.3 K at H = 0 (Fig.…”

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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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