<i>Ab initio</i>study of the CE magnetic phase in half-doped manganites: Purely magnetic versus double exchange description

Bastardis, Roland; Graaf, Coen de; Guihéry, Nathalie

doi:10.1103/physrevb.77.054426

Cited by 17 publications

(10 citation statements)

References 40 publications

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“…The extraction of the double exchange interactions is straightforward from wave function methods calculations of the lowest energy states . Due to the multideterminantal character of some of these states, it is much more complicate to determine these interactions from spin unrestricted DFT calculations.…”

Section: Introductionmentioning

confidence: 99%

In Search of Organic Compounds Presenting a Double Exchange Phenomenon

Chilkuri

Trinquier

Amor

et al. 2013

J. Chem. Theory Comput.

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The objective of this paper is to design a consistent series of organic molecules that may present a double exchange mechanism and study their low energy spectrum using spin unrestricted Density Functional Theory. For this purpose, organic tetra-methylene methane units having an S = 1 spin ground state and diamagnetic organic bridges are taken as building blocks for constructing molecules having two or more magnetic units. When biunit systems are ionized, the ground state of the resulting molecular ions may be either a quartet, if the spectrum is ruled by a double exchange mechanism, or a doublet, if it obeys the logic of a monoelectronic picture. A strategy based on the physical analysis of the leading interactions is followed in order to energetically favor a high-spin ground state. It is shown that the most promising compounds involve bridges that have both a large gap between the highest occupied and the lowest unoccupied molecular orbitals and small coefficients on the atoms to which the magnetic units are connected. While the followed strategy enables one to conceive organic compounds exhibiting a double exchange phenomenon, it is shown that the electronic mechanism ruling the spectrum of such organic double exchange compounds is different from that of their inorganic homologues. A new method to reconstruct the spectrum of low energy from various spin unrestricted DFT solutions is proposed and applied. Finally monodimensional and bidimensional periodic lattices based on the most promising organic architecture are suggested.

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Section: Introductionmentioning

confidence: 99%

In Search of Organic Compounds Presenting a Double Exchange Phenomenon

Chilkuri

Trinquier

Amor

et al. 2013

J. Chem. Theory Comput.

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“…Following the Heisenberg Hamiltonian model (H ˆ= À2J S i S ˆiÁS ˆi+1 ), J can be expressed as the energy difference between the lowest singlet and triplet states (2J = E S À E T ). The electrostatic environmental effects are known to play a major role in inorganic spin networks such as manganites, 17 cuprates 18 or spin-crossover iron(II) compounds. 19,20 Initially, it might be expected that the impact of this phenomenon in neutral organic crystalline materials is not as large as on systems based on paramagnetic transition metal centres.…”

Section: Introductionmentioning

confidence: 99%

Impact of short and long-range effects on the magnetic interactions in neutral organic radical-based materials

Domingo

Vérot

Mota

et al. 2013

Phys. Chem. Chem. Phys.

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The mutual influence of electronic structure and environment of the constituent units of neutral organic radical-based materials (radical dimers) is analysed by means of wave function calculations (Difference Dedicated Configuration Interaction, DDCI). Focus is put on the magnetic property modulations of two classes of neutral organic materials by inspecting both short- and long-range effects. The exchange coupling constant J for the high-temperature phase of the 1,3,5-trithia-2,4,6-triazapentalenyl (TTTA) material is calculated to be J= -95 cm(-1) at the DDCI level. The environmental electronic polarization is taken into account self-consistently using the individual polarizabilities of the atoms in a finite block of the crystal lattice (Discrete Reaction Field, DRF) and accounts for less than 5% of the calculated J value in TTTA. Furthermore, taking advantage of the chemical flexibility of the verdazyl radical family, the contribution of strong electron-withdrawing groups is analysed by extracting the J, U, t and K parameters from pairs of substituted verdazyl-based radicals. Our ab initio calculations of verdazyl radical pairs suggest that the addition of NO2 groups cause (i) the variations of the ferromagnetic and antiferromagnetic contributions to cancel out, leaving an almost constant exchange coupling constant, ca. J≈ 20 cm(-1), and that (ii) enhanced conduction properties can be anticipated. In contrast to inorganic analogues, one may conclude that the magnetic behaviour of neutral organic radical-based materials is mostly governed by the supramolecular arrangement, whereas environmental effects have a lesser impact.

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“…[1][2][3][4][5][6] Consequently, the interpretation of the underlying mechanisms has become a real challenge since promising properties can be anticipated in molecular magnetic as well as in extended networks. [7][8][9][10][11][12] One of the featuring characteristics of such systems is the temperaturedependent magnetic susceptibility that can be modeled phenomenologically by an exchange coupling constant J. The sign and amplitude of this parameter summarize the interactions between a limited number of localized spins.…”

Section: Introductionmentioning

confidence: 99%

Microscopic origins of the ferromagnetic exchange coupling in oxoverdazyl-based Cu(II) complex

Rota

Calzado

Train

et al. 2010

The Journal of Chemical Physics

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The exchange channels governing the experimentally reported coupling constant ͑J expt =6 cm −1 ͒ value in the verdazyl-ligand based Cu͑II͒ complex ͓Cu͑hfac͒ 2 ͑imvdz͔͒ are inspected using wave function-based difference dedicated configuration interaction calculations. The interaction between the two spin 1/2 holders is summed up in a unique coupling constant J. Nevertheless, by gradually increasing the level of calculation, different mechanisms of interaction are turned on step by step. In the present system, the calculated exchange interaction then appears alternatively ferromagnetic/ antiferromagnetic/ferromagnetic. Our analysis demonstrates the tremendously importance of some specific exchange mechanisms. It is actually shown that both parts of the imvdz ligand simultaneously influence the ferromagnetic behavior which ultimately reaches J calc = 6.3 cm −1 , in very good agreement with the experimental value. In accordance with the alternation of J, it is shown that the nature of the magnetic behavior results from competing channels. First, an antiferromagnetic contribution can be essentially attributed to single excitations involving the network localized on the verdazyl part. In contrast, the ligand-to-metal charge transfer ͑LMCT͒ involving the imidazole moiety affords a ferromagnetic contribution. The distinct nature / of the mechanisms is responsible for the net ferromagnetic behavior. The intuitively innocent part of the verdazyl-based ligands is deeply reconsidered and opens new routes into the rational design of magnetic objects.

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Ab initiostudy of the CE magnetic phase in half-doped manganites: Purely magnetic versus double exchange description

Cited by 17 publications

References 40 publications

In Search of Organic Compounds Presenting a Double Exchange Phenomenon

In Search of Organic Compounds Presenting a Double Exchange Phenomenon

Impact of short and long-range effects on the magnetic interactions in neutral organic radical-based materials

Microscopic origins of the ferromagnetic exchange coupling in oxoverdazyl-based Cu(II) complex

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