A first-principles bottom-up study of the magnetic interaction mechanism in the bulk ferromagnet p-O2N-C6F4-CNSSN

Jornet, Joaquim; Robb, Michael A.; Deumal, Mercè; Novoa, Juan J.

doi:10.1016/j.ica.2008.03.062

Cited by 7 publications

(2 citation statements)

References 21 publications

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“…We have used an abbreviated first principles approach, within which bulk magnetic properties are represented as a composite of the individual exchange interactions arising from all pairwise combinations of a radical and its nearest neighbors in the lattice. The method, which has been successfully applied to a variety of nitrogen-centered radicals, heterocyclic thiazyls, , selenazyls and phenalenyls, employs exchange energies estimated from broken symmetry DFT methods pioneered by Noodleman . Accordingly, and with reference to the formal Hamiltonian H ex = −2 J { S 1 · S 2 }, the exchange energy J for any pair of interacting radicals can be estimated from the total energies of the triplet ( E TS ) and broken symmetry singlet ( E BSS ) states and the respective expectation values ⟨ S 2 ⟩, according to eq .…”

Section: Resultsmentioning

confidence: 99%

Structure and Property Correlations in Heavy Atom Radical Conductors

Leitch

Winter

et al. 2009

J. Am. Chem. Soc.

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The synthesis and solid-state characterization of the resonance-stabilized heterocyclic thia/selenazyl radicals 1a-4a is described. While all the radicals crystallize in undimerized slipped pi-stacked arrays, the four crystal structures do not constitute an isomorphous set; crystals of 1a and 3a belong to the orthorhombic space group P2(1)2(1)2(1), while those of 2a and 4a belong to the monoclinic space group P2(1)/n. The origin of the structural dichotomy can be traced back to the packing of the radicals in the P2(1)/n structure, which maximizes intermolecular Se-Se' contacts. There are marked differences in the transport properties of the two groups. Variable temperature conductivity measurements reveal high, but activated, conductivity for the monoclinic pair (2a/4a), with sigma(298 K) > 10(-3) S cm(-1). The application of physical pressure increases the conductivity of both compounds, with sigma(298 K) at 5 GPa reaching 0.5 S cm(-1) for 2a and 2 S cm(-1) for 4a. Variable-temperature magnetic susceptibility measurements indicate strong antiferromagnetic (AFM) coupling for the monoclinic pair 2a and 4a, the behavior of which has been modeled in terms of a molecular-field modified 1D Heisenberg chain of AFM coupled S = 1/2 centers. Extended Huckel theory band structure calculations and density functional theory first principles methods have been used to develop a qualitative understanding of the conductive and magnetic properties of radicals of the type 1-4 as a function of the degree and direction of slippage of the radical pi-stacks.

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Section: Resultsmentioning

confidence: 99%

Structure and Property Correlations in Heavy Atom Radical Conductors

Leitch

Winter

et al. 2009

J. Am. Chem. Soc.

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“…The previous four-step procedure has been successfully applied to a wide range of molecule-based magnetic crystals. 16,69,111b-c,134-145 Among others, these studies cover molecule-based magnets that range from 0D 135 to 3D 16,69,140 MðHÞ ¼ ÀNgm B…”

Section: Cooperative Magnetic Interactions In Solidsmentioning

confidence: 99%

Calculation of microscopic exchange interactions and modelling of macroscopic magnetic properties in molecule-based magnets

2011

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The state-of-the-art theoretical evaluation and rationalization of the magnetic interactions (J(AB)) in molecule-based magnets is discussed in this critical review, focusing first on isolated radical···radical pair interactions and afterwards on how these interactions cooperate in the solid phase. Concerning isolated radical pairwise magnetic interactions, an initial analysis is done on qualitative grounds, concentrating also on the validity of the most commonly used models to predict their size and angularity (namely, McConnell-I and McConnell-II models, overlap of magnetic orbitals,…). The failure of these models, caused by their oversimplified description of the magnetic interactions, prompted the introduction of quantitative approaches, whose basic principles and relative quality are also evaluated. Concerning the computation of magnetic interactions in solids, we resort to a sum of pairwise magnetic interactions within the Heisenberg Hamiltonian framework, and follow the First-principles Bottom-Up procedure, which allows the accurate study of the magnetic properties of any molecule-based magnet in an unbiased way. The basic principles of this approach are outlined, applied in detail to a model system, and finally demonstrated to properly describe the magnetic properties of molecule-based systems that show a variety of magnetic topologies, which range from 1D to 3D (152 references).

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Studying the Origin of the Antiferromagnetic to Spin‐Canting Transition in the β‐p‐NCC₆F₄CNSSN^.Molecular Magnet

Deumal

Rawson

Goeta

et al. 2010

Chemistry A European J

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The crystal structure of the spin-canted antiferromagnet beta-p-NCC(6)F(4)CNSSN* at 12 K (reported in this work) was found to adopt the same orthorhombic space group as that previously determined at 160 K. The change in the magnetic properties of these two crystal structures has been rigorously studied by applying a first-principles bottom-up procedure above and below the magnetic transition temperature (36 K). Calculations of the magnetic exchange pathways on the 160 K structure reveal only one significant exchange coupling (J(d1)=-33.8 cm(-1)), which generates a three-dimensional diamond-like magnetic topology within the crystal. The computed magnetic susceptibility, chi(T), which was determined by using this magnetic topology, quantitatively reproduces the experimental features observed above 36 K. Owing to the anisotropic contraction of the crystal lattice, both the geometry of the intermolecular contacts at 12 K and the microscopic J(AB) radical-radical magnetic interactions change: the J(d1) radical-radical interaction becomes even more antiferromagnetic (-43.2 cm(-1)) and two additional ferromagnetic interactions appear (+7.6 and +7.3 cm(-1)). Consequently, the magnetic topologies of the 12 and 160 K structures differ: the 12 K magnetic topology exhibits two ferromagnetic sublattices that are antiferromagnetically coupled. The chi(T) curve, computed below 36 K at the limit of zero magnetic field by using the 12 K magnetic topology, reproduces the shape of the residual magnetic susceptibility (having subtracted the contribution to the magnetization arising from spin canting). The evolution of these two ferromagnetic J(AB) contributions explains the change in the slope of the residual magnetic susceptibility in the low-temperature region.

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A first-principles bottom-up study of the magnetic interaction mechanism in the bulk ferromagnet p-O2N-C6F4-CNSSN

Cited by 7 publications

References 21 publications

Structure and Property Correlations in Heavy Atom Radical Conductors

Structure and Property Correlations in Heavy Atom Radical Conductors

Calculation of microscopic exchange interactions and modelling of macroscopic magnetic properties in molecule-based magnets

Studying the Origin of the Antiferromagnetic to Spin‐Canting Transition in the β‐p‐NCC₆F₄CNSSN^.Molecular Magnet

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A first-principles bottom-up study of the magnetic interaction mechanism in the bulk ferromagnet p-O2N-C6F4-CNSSN

Cited by 7 publications

References 21 publications

Structure and Property Correlations in Heavy Atom Radical Conductors

Structure and Property Correlations in Heavy Atom Radical Conductors

Calculation of microscopic exchange interactions and modelling of macroscopic magnetic properties in molecule-based magnets

Studying the Origin of the Antiferromagnetic to Spin‐Canting Transition in the β‐p‐NCC6F4CNSSN.Molecular Magnet

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Product

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Studying the Origin of the Antiferromagnetic to Spin‐Canting Transition in the β‐p‐NCC₆F₄CNSSN^.Molecular Magnet