Magnetoelastic Instability in Molecular Antiferromagnetic Rings

Parola, Alberto

doi:10.1103/physrevlett.92.197202

Cited by 18 publications

(43 citation statements)

References 22 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The behaviour of a cluster of spins in the presence of spin-phonon coupling depends on the number of sites and on the spin value [3]. However, this paper concentrates on the effects of the quantum nature of the phonons and for this purpose, we restrict ourselves to a ring of 4 spins where the atoms can only move along the ring.…”

Section: Modelmentioning

confidence: 99%

“…This kind of systems in the presence of spin-phonon coupling was already studied with a classical treatment of the phonons [3]. In this paper, we pay special attention to the quantum nature of the phonons and show that some important departures from the classical picture may occur, depending on the different parameters which are the phonons frequency, the exchange interactions and the spin-phonon coupling.…”

Section: Introductionmentioning

confidence: 99%

“…These instabilities with respect to a spontaneous distortion of the lattice for any value of the spin-phonon coupling are special cases, and in standard systems there is a finite critical value of the spin-phonon coupling above which the system will be distorted. It is in particular the case for finite systems such as rings consisting of a small number of spins [3]. In the case of a degenerate ground state, a distortion lifting this degeneracy is very likely to occur, which is the Jahn-Teller effect.…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Dynamic spin Jahn-Teller effect in small magnetic clusters

Elhajal

Mila

2005

Eur. Phys. J. B

View full text Add to dashboard Cite

Abstract. We study the effect of spin-phonon coupling in small magnetic clusters, concentrating on a S=1/2 ring of 4 spins coupled antiferromagnetically. If the phonons are treated as classical variables, there is a critical value of the spin-phonon coupling above which a static distortion occurs. This is a good approximation if the zero point energy is small compared to the energy gain due to the distortion, which is true for large exchange interactions compared to the phonons energy (J ≫ ω). In the opposite limit, one can integrate out the phonon degrees of freedom and get an effective spin hamiltonian. Using exact diagonalizations to include the quantum nature of both spins and phonons, we obtain the spectrum in the whole range of parameters and explicit the crossover between the classical and quantum regimes. We then establish quantitatively the limits of validity of two widely used approaches (one in the quantum and one in the classical limits) and show that they are quite poor for small magnetic clusters. We also show that upon reducing ω/J the first excitation of a 4-site cluster becomes a singlet, a result that could be relevant for Cu2Te2O5Br2.PACS. 70 Condensed matter: electronic structure, electrical, magnetic, and optical properties -75 Magnetic properties and materials -75.75.+a Magnetic properties of nanostructures -75.45.+j Macroscopic quantum phenomena in magnetic systems 1 introduction

show abstract

Section: Modelmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Dynamic spin Jahn-Teller effect in small magnetic clusters

Elhajal

Mila

2005

Eur. Phys. J. B

View full text Add to dashboard Cite

show abstract

“…In comparison with antiferromagnetic rings [17,29,30,31,32], ferromagnetic ones have so far much less been calculated microscopically. Many of antiferromagnetic features were derived from isotropic Hamiltonians and were hardly compared with corresponding experimental observations.…”

mentioning

confidence: 99%

“…On the other hand, 63 Cu nuclear quadrupole resonance spectra of Cu8 rings indicate four crystallographically inequivalent Cu II ions in each ring, which is attributable to the slight deviation of Cu II ions from a planar octagon [23] and/or possible distortion of the octagonal environment due to spin-lattice coupling [29]. Hence, we introduce a DM term into the Hamiltonian of Cu8 and show the resultant 1/T 1 in Fig.…”

mentioning

confidence: 99%

Spin Dynamics in Molecular Ring Nanomagnets: Significant Effect of Acoustic Phonons and Magnetic Anisotropies

Yamamoto

Hikihara

2006

J. Phys. Soc. Jpn.

View full text Add to dashboard Cite

The nuclear spin-lattice relaxation rate 1/T1 is calculated for magnetic ring clusters by fully diagonalizing their microscopic spin Hamiltonians. Whether the nearest-neighbor exchange interaction J is ferromagnetic or antiferromagnetic, 1/T1 versus temperature T in ring nanomagnets may be peaked at kBT ≃ |J| provided the lifetime broadening of discrete energy levels is in proportion to T 3 . Experimental findings for ferromagnetic and antiferromagnetic Cu II rings are reproduced with crucial contributions of magnetic anisotropies as well as acoustic phonons. and therefore, serve to reveal a quantum-to-classical crossover between molecular and bulk magnets [6].Nuclear magnetic resonance (NMR) is an effective probe of low-energy spin dynamics, and the nuclear spinlattice relaxation time T 1 has been measured for various molecular wheels [7,8,9,10,11,12,13,14,15]. Interestingly, 1/T 1 as a function of temperature T under a fixed field H is commonly peaked at k B T ≃ |J|, where J is the intracluster exchange interaction between neighboring ion spins. Baek et al. [12] have recently provided a key to this long-standing problem by reanalyzing extensive observations of antiferromagnetic rings. When 1/T 1 is divided by the static susceptibility-temperature product χT , its peak is more pronounced and well-fitted to the Lorentzian-type expression,where ω N ≡ γ N H is the Larmor frequency of probe nuclei, whereas ω c is what they define as the temperaturedependent correlation frequency. The renormalized relaxation rate is thus peaked at a temperature satisfying ω c (T ) ≃ ω N (H). Considering the significant difference between the electronic and nuclear energy scales (hω N < ∼ 10 −5 |J|),hω c (T ) may be ascribed to the averaged lifetime broadening of discrete energy levels. Demonstrating that chromic and ferric wheels give ω c ∝ T α with α = 3.0 ∼ 3.5, Baek et al. claim that the exchangecoupled ion spins are likely to interact with the host molecular crystal through the Debye-type phonons.In response to this stimulative report, several authors [16,17] inquired further into the underlying scenario. While their arguments were elaborately based on microscopic spin Hamiltonians and enlighteningly verified the relevance of spin-phonon coupling to the notably peaked 1/T 1 , any magnetic anisotropy was neglected and/or most of the transition matrix elements were discarded in their evaluation of the dynamic spin correlation functions. Thus, we take the naivest but thus cumbersome approach: We set up realistically dressed Hamiltonians, completely diagonalize them, and sum up all the transition matrix elements into the dynamic structure factor. Such calculations are inevitably restricted to sufficiently small clusters but can nevertheless illuminate key factors in nanoscale spin dynamics, intrinsic intracluster anisotropies and extrinsic intercluster phonons.We consider both ferromagnetic and antiferromagnetic rings of various metal ion spins and describe them by the Hamiltonian |A στ q | 2 is the form factor describing the hyper...

show abstract

Structural and magnetic investigations on new molecular quantum rings

Pashchenko

Lang

Wolf

et al. 2006

Comptes Rendus. Chimie

View full text Add to dashboard Cite

We report on a comparative investigation of the structural and magnetic properties of three oxygen-bridged polynuclear (N ¼ 6, 8, 10) Cu(II) cyclomethylsiloxanolate complexes, Cu 6 [(MeSiO 2 ) 6 ] 2 $6DMF (1), {Cu 8 [(MeSiO 2 ) 8 ] 2 $8DMF}$EtOH (2) and {Cu 10 [(MeSiO 2 ) 10 ] 2 $10DMF}$6DMF (3). All three molecular complexes have a planar ring-shaped configuration of the copper S ¼ 1/2 spins. The analysis of the magnetic data, with particular emphasis placed on the high-temperature behaviour, together with the structural information enables us to correlate the evolution of the exchange coupling J between the magnetic S ¼ 1/2 centers of the quantum ring as a function of the number N of magnetic sites to the structural changes of the molecular crystals.

show abstract

Magnetoelastic Instability in Molecular Antiferromagnetic Rings

Cited by 18 publications

References 22 publications

Dynamic spin Jahn-Teller effect in small magnetic clusters

Dynamic spin Jahn-Teller effect in small magnetic clusters

Spin Dynamics in Molecular Ring Nanomagnets: Significant Effect of Acoustic Phonons and Magnetic Anisotropies

Structural and magnetic investigations on new molecular quantum rings

Contact Info

Product

Resources

About