Quantum signatures of a molecular nanomagnet in direct magnetocaloric measurements

Sharples, Joseph W.; Collison, David; McInnes, Eric J. L.; Schnack, Jürgen; Palacios, E.; Evangelisti, Marco

doi:10.1038/ncomms6321

Cited by 121 publications

(95 citation statements)

References 31 publications

(57 reference statements)

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“…Continuous changes of configurations start (and end, in the case of centered rings) at the well-determined critical value of α, independent on system size for centered rings. It should to be stressed that these obtained for the second of models, |α c | 4, are identical as those found in their quantum counterparts [16,19,20]. Basing on numerical results, it can be said that the first critical value for quantum rings with a defect bond tends to calculated here α c 1{pn¡1q (see Fig.…”

Section: Discussionmentioning

confidence: 53%

“…In this paper two such systems are presented: antiferromagnetic odd-numbered rings and rings with an even number of spins uniformly coupled to an extra one. The first case is related to the Cr 9 molecule [10], whereas the other is a model of Fe 7 or Gd 7 molecule [19,20]. In these cases there is a welldetermined domain with the collinear LEC despite the presence of frustration and this configuration is the same as in the absence of frustration.…”

Section: Introductionmentioning

confidence: 99%

“…The corresponding energies are ¡npα 2 {8 1q and ¡np|α|¡1q|, for |α| ¤ 4 and |α| ¥ 4, respectively. [16,19,20].…”

Section: Centered Ringsmentioning

confidence: 99%

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Collinear and Non-Collinear Configurations in Classical Geometrically Frustrated Ring-Shaped Systems

et al. 2018

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Geometrically frustrated quantum spin systems, with competing antiferromagnetic couplings, show the Kahn degenerate frustration for some specific values of Heisenberg Hamiltonian parameters. It has been recently shown for rings with a defect bond and centered rings. In the case of classical counterparts of these systems, degenerated configurations with the lowest energy are present for the energy function parameter greater than a certain threshold. In these domains such configurations are planar but non-collinear with continuous changes of the net magnetic moment with respect to the Hamiltonian parameter. Outside these domains there is unique collinear ground state configuration (neglecting choice of the net magnetic moment direction). However, these collinear configurations are the same in both non-frustrated and geometrically frustrated domains. Numerically exact calculations for quantum systems strongly confirm that determined properties of their classical counterparts realize the classical limit s Ñ 8.

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Section: Discussionmentioning

confidence: 53%

Section: Introductionmentioning

confidence: 99%

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Collinear and Non-Collinear Configurations in Classical Geometrically Frustrated Ring-Shaped Systems

et al. 2018

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“…As one can see, the entropy changes for ΔB = 7 T are very similar for the actual α = 0.65 of 1 (red) and the critical value of α c = 0.7 (dashed red). The very steep rise at the lowest temperatures signals that this compound should be a powerful cooler at liquid helium temperatures [40][41][42] with impressive MCE figures for a single molecule unit [ΔS = S(7 T)-S(0 T) > 20 R at T≈3 K]. This behaviour is compared in Fig.…”

Section: -37mentioning

confidence: 93%

High spin cycles: topping the spin record for a single molecule verging on quantum criticality

et al. 2018

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The cyclisation of a short chain into a ring provides fascinating scenarios in terms of transforming a finite array of spins into a quasiinfinite structure. If frustration is present, theory predicts interesting quantum critical points, where the ground state and thus lowtemperature properties of a material change drastically upon even a small variation of appropriate external parameters. This can be visualised as achieving a very high and pointed summit where the way down has an infinity of possibilities, which by any parameter change will be rapidly chosen, in order to reach the final ground state. Here we report a mixed 3d/4f cyclic coordination cluster that turns out to be very near or even at such a quantum critical point. It has a ground state spin of S = 60, the largest ever observed for a molecule (120 times that of a single electron). [Fe 10 Gd 10 (Me-tea) 10 (Me-teaH) 10 (NO 3 ) 10 ]·20MeCN forms a nano-torus with alternating gadolinium and iron ions with a nearest neighbour Fe-Gd coupling and a frustrating next-nearest neighbour Fe-Fe coupling. Such a spin arrangement corresponds to a cyclic delta or saw-tooth chain, which can exhibit unusual frustration effects. In the present case, the quantum critical point bears a 'flatland' of tens of thousands of energetically degenerate states between which transitions are possible at no energy costs with profound caloric consequences. Entropy-wise the energy flatland translates into the pointed summit overlooking the entropy landscape. Going downhill several target states can be reached depending on the applied physical procedure which offers new prospects for addressability.

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“…Anyway, the calculations reported below are all performed by considering the whole Hamiltonian (2), including DM interaction. The field-dependence of the energy levels, calculated by using Hamiltonian (2), is shown in Fig. 2.…”

Section: Theorymentioning

confidence: 99%

Low temperature magnetic properties and spin dynamics in single crystals of Cr8Zn antiferromagnetic molecular rings

Adelnia

Chiesa

Bordignon

et al. 2015

The Journal of Chemical Physics

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Articles you may be interested inHigh temperature spin dynamics in linear magnetic chains, molecular rings, and segments by nuclear magnetic resonance J. Appl. Phys. 117, 17B308 (2015) A detailed experimental investigation of the effects giving rise to the magnetic energy level structure in the vicinity of the level crossing (LC) at low temperature is reported for the open antiferromagnetic molecular ring Cr 8 Zn. The study is conducted by means of thermodynamic techniques (torque magnetometry, magnetization and specific heat measurements) and microscopic techniques (nuclear magnetic resonance line width, nuclear spin lattice, and spin-spin relaxation measurements). The experimental results are shown to be in excellent agreement with theoretical calculations based on a minimal spin model Hamiltonian, which includes a Dzyaloshinskii-Moriya interaction. The first ground state level crossing at µ 0 H c1 = 2.15 T is found to be an almost true LC while the second LC at µ 0 H c2 = 6.95 T has an anti-crossing gap of ∆ 12 = 0.19 K. In addition, both NMR and specific heat measurements show the presence of a level anti-crossing between excited states at µ 0 H = 4.5 T as predicted by the theory. In all cases, the fit of the experimental data is improved by introducing a distribution of the isotropic exchange couplings (J), i.e., using a J strain model. The peaks at the first and second LCs in the nuclear spin-lattice relaxation rate are dominated by inelastic scattering and a value of Γ ∼ 10 10 rad/s is inferred for the life time broadening of the excited state of the open ring, due to spin phonon interaction. A loss of NMR signal (wipe-out effect) is observed for the first time at LC and is explained by the enhancement of the spin-spin relaxation rate due to the inelastic scattering. C 2015 AIP Publishing LLC. [http://dx

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Quantum signatures of a molecular nanomagnet in direct magnetocaloric measurements

Cited by 121 publications

References 31 publications

Collinear and Non-Collinear Configurations in Classical Geometrically Frustrated Ring-Shaped Systems

Collinear and Non-Collinear Configurations in Classical Geometrically Frustrated Ring-Shaped Systems

High spin cycles: topping the spin record for a single molecule verging on quantum criticality

Low temperature magnetic properties and spin dynamics in single crystals of Cr8Zn antiferromagnetic molecular rings

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