Neutron scattering and magnetic observables for<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mi>S</mml:mi><mml:mo>=</mml:mo><mml:mn>1</mml:mn><mml:mo>∕</mml:mo><mml:mn>2</mml:mn></mml:mrow></mml:math>spin clusters and molecular magnets

Haraldsen, J. T.; Barnes, T.; Musfeldt, J. L.

doi:10.1103/physrevb.71.064403

Cited by 83 publications

(105 citation statements)

References 36 publications

(50 reference statements)

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“…The full quantum mechanical structure factor can be evaluated by summing over the S tot ϭ 1 excited states (22) to obtain S(Q) ϭ 1 Ϫ cos 2 (Qx/2) cos 2 (Qy /2). (e) Portion of the infinite square lattice ground state, viewed as the Neé l state (weight ) with quantum corrections (weights n), of which one resonating valence bond configuration is sketched.…”

Section: Resultsmentioning

confidence: 99%

Quantum dynamics and entanglement of spins on a square lattice

Christensen

Rønnow

McMorrow

et al. 2007

Proc. Natl. Acad. Sci. U.S.A.

133

151

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Bulk magnetism in solids is fundamentally quantum mechanical in nature. Yet in many situations, including our everyday encounters with magnetic materials, quantum effects are masked, and it often suffices to think of magnetism in terms of the interaction between classical dipole moments. Whereas this intuition generally holds for ferromagnets, even as the size of the magnetic moment is reduced to that of a single electron spin (the quantum limit), it breaks down spectacularly for antiferromagnets, particularly in low dimensions. Considerable theoretical and experimental progress has been made in understanding quantum effects in one-dimensional quantum antiferromagnets, but a complete experimental description of even simple two-dimensional antiferromagnets is lacking. Here we describe a comprehensive set of neutron scattering measurements that reveal a non-spin-wave continuum and strong quantum effects, suggesting entanglement of spins at short distances in the simplest of all two-dimensional quantum antiferromagnets, the square lattice Heisenberg system. antiferromagnetism ͉ entanglement ͉ multimagnons ͉ spin waves O ne of the most fundamental exercises in quantum mechanics is to consider a pair of S ϭ 1/2 spins with an interaction J between them that favors either parallel (ferromagnetic) or antiparallel (antiferromagnetic) alignment. The former results in a spin S tot ϭ 1 ground state, which is a degenerate triplet. Two of the states in this triplet are the possible classical ground states ͉11͘ and ͉22͘, whereas the third is the coherent symmetric superposition ͉12͘ϩ͉21͘, which has no classical analogue. Even more interesting is antiferromagnetic J, for which the ground state is the entirely nonclassical S tot ϭ 0 singlet ͉0͘ ϭ ͉12͘ Ϫ ͉21͘ consisting of the antisymmetric coherent superposition of the two classical ground states of the pair. The state ͉0͘ is an example of maximal entanglement, i.e., a wavefunction for two coupled systems that cannot be written as the product of eigenfunctions for the two separate systems, which in this case are of course the two spins considered individually.

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Section: Resultsmentioning

confidence: 99%

Quantum dynamics and entanglement of spins on a square lattice

Christensen

Rønnow

McMorrow

et al. 2007

Proc. Natl. Acad. Sci. U.S.A.

133

151

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“…Although, if the ground state degeneracy is broken for the equilateral triangle, then that transition will be that of a dimer (1 − cos( q · r 13 )) 31 . The spin-0 transition for the square (|0 I → |0 II ) has zero intensity because it is forbidden due to geometric selection rule restrictions put on by cluster excitations 35 .…”

Section: Inelastic Neutron Scattering Structure Factorsmentioning

confidence: 99%

“…(8) run over all magnetic ions in one unit cell, and a, b are the spatial indices of the spin operators 31 .…”

Section: Inelastic Neutron Scattering Structure Factorsmentioning

confidence: 99%

“…However, this system has been exhaustively investigated by a number of studies [28][29][30] . In 2005, the excitations of dimers, trimers, and tetramers were examined in detail 31 . Typically, the magnetic properties and inelastic structures factors for different geometries are determined on a case-by-case basis or numerically on larger systems 20,32-34 , which does not provide any insight into the scalability and growth of these systems.…”

Section: Introductionmentioning

confidence: 99%

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Evolution of thermodynamic properties and inelastic neutron scattering intensities for spin-12antiferromagnetic quantum rings

Haraldsen

2016

Phys. Rev. B

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This study examines the increasing complexity in the magnetic properties of small n = 3, 4, 5, 6 spin-1/2 quantum rings. Using an exact diagonalization of the isotropic Heisenberg Hamiltonian with nearest and next-nearest neighbor interactions, the energy eigenstates, magnetic specific heat capacity, magnetic susceptibility, and inelastic neutron scattering structure factors are determined for variable next-nearest neighbor interactions. Here, it is shown that the presence of a complex spinmixing, multiple ground states, and non-zero ground states greatly complicate the spin Hamiltonian. Overall, the energy eigenstates and structure factor intensities are presented in closed form, while the thermodynamic properties detail the effect of a crossing interaction in the rings. The goal of this work is to provide insight into the evolution of the magnetic properties and spin excitations within these systems.

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“…Spin 1/2 clusters have been studied in great detail by a number of theoretical and experimental groups [30][31][32][33][34][35] . With regards to the spin dimer, Whangbo et al presents a detailed analysis of general excitations 31 ; however, this work doesn't examine the changes in the inelastic neutron scattering intensities.…”

mentioning

confidence: 99%

Generalization of polarized spin excitations for asymmetric dimeric systems

Houchins

Haraldsen

2015

Phys. Rev. B

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Through the use of Heisenberg spin-spin interactions, we provide analytical representations for inelastic neutron scattering eigenstates and excitation cross-sections of the general S1-S2 spin dimeric systems. Using an exact diagonalization approach to the spin Hamiltonian, we analyze various spin coefficients to provide general representations for the neutron scattering cross-sections of two interacting spins. We also detail a generalized method for the determination of Sz polarized excitations, which provide an approximation for the excitations within an applied magnetic field. These calculations provide a general understanding of the interactions between two individual or compound spin systems, which can help provide insight into condensed matter systems like molecular magnets, quantum dots, and spintronic systems, as well as particle physics investigations into quark matter and meson interactions. * Corresponding Author: Dr. Jason T. Haraldsen (haraldjt@jmu.edu) PACS numbers: 75.30.Et,75.50.Ee,75.50.Xx,78.70.Nx The study of quantum nanomagnets has been expanding rapidly due to the possible technological applications for systems like molecular magnets and quantum dots due to the presence of quantum tunneling phenomena and anisotropic effects.1-10 The complete understanding of quantum excitations and the ability to detect and observe them are two critical components for the development of applications in spintronics and spin switches for quantum computing 10,11 .Molecular magnets are clusters of magnetic ions that are typically isolated from long-range magnetic interactions by non-magnetic ligands [12][13][14][15][16][17][18][19] , and they typically have many magnetic ions like Mn 12 and V 15 15,16 . Recently, it has been shown that many excitations within large magnetic clusters are governed by individual subgeometry (smaller two-and three-body components) excitations 20 . Therefore, examining the smallest components of magnetic interactions is critical for moving forward in gaining information for the larger and more complex systems.From an experimental point of view, there are many techniques that can be employed to characterize and measure the properties of antiferromagnetic spin systems. These include magnetic susceptibility, inelastic neutron scattering (INS), optical/Raman spectroscopy, and electron spin resonance. 19,21,22 While many of these techniques are important for the study of the bulk properties for magnetic systems, INS provides the unique ability to investigate individual excitations and examine local interactions and structural data.Typically, discussions of magnetic clusters are limited to specific material systems [23][24][25][26][27][28][29] , which doesn't always provide a complete picture of the interactions being studied. Spin 1/2 clusters have been studied in great detail by a number of theoretical and experimental groups [30][31][32][33][34][35] . With regards to the spin dimer, Whangbo et al. presents a detailed analysis of general excitations 31 ; however, this work doesn't exa...

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Neutron scattering and magnetic observables forS=1∕2spin clusters and molecular magnets

Cited by 83 publications

References 36 publications

Quantum dynamics and entanglement of spins on a square lattice

Quantum dynamics and entanglement of spins on a square lattice

Evolution of thermodynamic properties and inelastic neutron scattering intensities for spin-12antiferromagnetic quantum rings

Generalization of polarized spin excitations for asymmetric dimeric systems

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