Targeting Exchange Interactions in Nanosize Molecular Magnets by Angular Momentum Technique

Palii, Andrew; Tsukerblat, Boris

doi:10.1016/b978-0-12-409547-2.14779-1

Cited by 2 publications

(3 citation statements)

References 135 publications

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“…The eigenvalues of the Hamiltonian, eq , as functions of the driver-cell polarization P 2 are given in Table . To rationalize the results, it is worth referring to the concept of the group-theoretical assignation of the spin multiplets, − which provides us with the interrelation between the eigenstates of the model t–J -Hamiltonian and exact terms of the systems enumerated by the irreducible representations of the point group and full spins. Here, we need only restricted information from the group-theoretical assignation of the free cell states that allows us to qualitatively distinguish the state of the system according to their polarizability by the driver’s field.…”

Section: Discussionmentioning

confidence: 99%

Mixed-Valence Magnetic Molecular Cell for Quantum Cellular Automata: Prospects of Designing Multifunctional Devices through Exploration of Double Exchange

et al. 2020

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In this article, we propose to use multielectron square-planar mixedvalence (MV) molecules as molecular cells for quantum cellular automata (QCA) devices. As distinguished from previous proposals in this area, in multielectron cells, the electronic pair encoding binary information is shared among localized spins ("spin cores"). Hopefully, this will allow exploring not only charge degrees of freedom encoding binary information in the antipodal electronic distributions but also spin degrees of freedom through the magnetic interactions such as double exchange and Heisenberg−Dirac−Van Vleck (HDVV) exchange. To develop the proposed route, the square-planar tetrameric cells for QCA have been theoretically modeled. The considered cells comprise a pair of excess electrons shared among four spin cores and hence they exhibit double exchange and HDVV exchange. Such cells can be based either on the square-planar mixed-valence molecular clusters or on the similar square arrays of multielectron quantum dots. The detailed case study of the cell representing the transition-metal tetramer of the type of d 2 −d 2 −d 1 −d 1 shows that depending on the relative strength of the second-order double exchange and HDVV exchange, the isolated cell has either ground localized spin-triplet or one of the two delocalized spin-singlets, exhibiting different extents of electron delocalization. Due to different sensitivities of these states to the quadrupole electrostatic field induced by the polarized neighboring driver cell, the latter is shown to be able to produce switching between different ground states (including spin-switching between spin-singlet and spin-triplet), which leads to the nonmonotonic behavior of the cell−cell response function. This opens new perspectives for the designing of multifunctional devices combining the QCA functionality with spin-switching function.

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Section: Discussionmentioning

confidence: 99%

Mixed-Valence Magnetic Molecular Cell for Quantum Cellular Automata: Prospects of Designing Multifunctional Devices through Exploration of Double Exchange

et al. 2020

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“…The total spin of such tetramer consisting of two spins 1/2 and two spins 1, takes the values: S = 3, 2, 1, 0. The calculation of the energy spectrum can be performed with the aid of angular momentum approach (see review articles) [31,32] and MVPACK program based on this approach [33]. In order to elucidate the effect of the double exchange we present in Figure 3 the energy spectrum calculated within the basic model taking into account only the double exchange and the Coulomb repulsion (the HDVV exchange will be included in consideration later on).…”

Section: Combined Effect Of the Double Exchange And Coulomb Repulsionmentioning

confidence: 99%

“…Then by coupling the states of the localized and delocalized units one can conclude that the term of the d 2 − d 2 − d 1 − d 1 tetramer with the maximal spin S = 3 is 7 E. One can see from the Table 1 that the degeneracy of two S = 3 states is related to the orbital degeneracy which means that this is an "exact" degeneracy originating from the point symmetry of the system. A comprehensive discussion of the degeneracies in spin systems and their physical consequences can be found in review articles [31,32]. In particular, one can observe the so-called "accidental degeneracy" interrelated with the unitary symmetry that in general are high than the point one.…”

Section: Double Exchange In Regime Of Strong Coulomb Repulsionmentioning

confidence: 99%

Can the Double Exchange Cause Antiferromagnetic Spin Alignment?

et al. 2020

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The effect of the double exchange in a square-planar mixed-valence dn+1−dn+1−dn−dn–type tetramers comprising two excess electrons delocalized over four spin cores is discussed. The detailed analysis of a relatively simple d2−d2−d1−d1–type tetramer shows that in system with the delocalized electronic pair the double exchange is able to produce antiferromagnetic spin alignment. This is drastically different from the customary ferromagnetic effect of the double exchange which is well established for mixed-valence dimers and tetramers with one excess electron or hole. That is why the question “Can double exchange cause antiferromagnetic spin alignment?” became the title of this article. As an answer to this question the qualitative and quantitative study revealed that due to antiparallel directions of spins of the two mobile electrons which give competitive contributions to the overall polarization of spin cores, the system entirely becomes antiferromagnetic. It has been also shown that depending on the relative strength of the second-order double exchange and Heisenberg–Dirac–Van Vleck exchange the system has either the ground localized spin-triplet or the ground delocalized spin-singlet.

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Targeting Exchange Interactions in Nanosize Molecular Magnets by Angular Momentum Technique

Cited by 2 publications

References 135 publications

Mixed-Valence Magnetic Molecular Cell for Quantum Cellular Automata: Prospects of Designing Multifunctional Devices through Exploration of Double Exchange

Mixed-Valence Magnetic Molecular Cell for Quantum Cellular Automata: Prospects of Designing Multifunctional Devices through Exploration of Double Exchange

Can the Double Exchange Cause Antiferromagnetic Spin Alignment?

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