Molecular design of organic ferrimagnets

Shiomi, Daisuke; Nishizawa, M.; Kamiyama, Kenji; Hase, Syuichiro; Kanaya, T.; Sato, Kazunobu; Takui, Takeji

doi:10.1016/s0379-6779(00)00960-7

Cited by 15 publications

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“…With further decreasing temperature, the χ T value increases to a maximum and then drops rapidly, which gives rise to the curves of the product χ T against temperature showing as a round peak at low temperatures. This phenomenon is well consistent with the recent experimental observations on some genuinely organic molecule-based ferrimagnetics. ,, It is clear that the peak is very sensitive to the changing of the intermolecular antiferromangnetic interactions J 2 and J 2 ′. With increasing of J 2 and J 2 ′, the peak is suppressed and moves toward higher temperature region.…”

Section: Resultssupporting

confidence: 91%

Nature of the Ferromagnetic Behavior and Possible Occurrence of the Ferrimagnetic Phase Transition in Genuinely Organic Molecule-Based Assemblages with an S = 1 and S = ¹/ ₂ Antiferromagnetic Alternating Spin Chain: A Green’s Function Approach

Yao

Liu

2008

J. Phys. Chem. A

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The temperature dependence of magnetic susceptibility and sublattice magnetizations were calculated for a Heisenberg Hamiltonian of an S = 1 and S = 1/2 antiferromagnetic alternating spin chain by means of the many-body Green's function theory to show the possible occurrence of a ferrimagnetic phase transition for genuinely organic molecule-based magnets. The S = 1 site in the chain is composed of two S = 1/2 spins coupled by a finite ferromagnetic interaction. From the calculated results, it is found that the sublattice magnetization at low-spin S = 1/2 sites changes its sign from negative to positive with increasing temperature, giving rise to the spin alignments along the chain changing from antiferromagnetic to ferromagnetic ones, which indicates that there is a magnetic phase transition occurring. Because of the weak intermolecular antiferromagnetic interactions, the curves of the magnetic susceptibility multiplied by temperature (chiT) against temperature show a round peak at low temperatures, which is well consistent with recent experimental observations, and the ferrimagnetic phase transition could only be detected at an ultralow-temperature region and under very weak external magnetic fields in practical organic materials. From the analysis of the sublattice magnetizations, it is uncovered that the appearance of the low-temperature peak in the curves of the chiT originates from the ferromagnetic spin alignments for all the spins along the chain, and the intermolecular antiferromagnetic interactions play a pivotal role in ferrimagnetic spin alignments of the magnetic systems. It is also found that the higher spatial symmetry of the intermolecular antiferromagnetic interactions have contributions to stabilize the ferrimagnetic ordering state in the molecule-based magnetic materials.

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Section: Resultssupporting

confidence: 91%

Nature of the Ferromagnetic Behavior and Possible Occurrence of the Ferrimagnetic Phase Transition in Genuinely Organic Molecule-Based Assemblages with an S = 1 and S = ¹/ ₂ Antiferromagnetic Alternating Spin Chain: A Green’s Function Approach

Yao

Liu

2008

J. Phys. Chem. A

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“…Thus, the molecular design serving for the syntheses of the organic ferrimagnets is a challenging issue in materials science. We have examined the possible occurrence of the ferrimagnetic spin alignments in organic molecular assemblages both by experiments and by theoretical calculations in quantum terms [24][25][26][27][28][29][30][31][32].…”

Section: Single-component Ferrimagnetsmentioning

confidence: 99%

Hyperfine structure of ESR spectra as a probe for heisenberg exchange couplings in nitroxide triradicals serving as building blocks for molecule-based ferrimagnets

et al. 2003

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A study on electron spin resonance (ESR) spectroscopic determination of exchange interactions in organic oligoradicals is given. When the intramolecular exchange coupling J between unpaired electron spins in nitroxide-based oligoradicals falls within the order of 10 Oe (1 mK or 10 -3 cm -~ for g = 2), which is on the same order as the hyperfine coupling A of magnetic nuclei such as nitrogen atoms of nitroxide radicals, the magnitude of J can be determined from the hyperfine splitting pattern of ESR spectra in solutions. This range of the exchange coupling J is not detectable in conventional magnetic susceptibility measurements. We demonstrate an application of hyperfine ESR spectroscopy as a probe for the exchange coupling to a series of organic oligoradicals, which the authors have recently developed as building blocks for molecule-based magnetic materials.

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“…As a purposive molecular designing for cocrystallizing distinct molecules with different spin quantum numbers in a solid state, we have proposed a strategy of “single-component ferrimagnetics”: − When a π-biradical with a triplet ( S = 1) ground state and a π-radical with S = 1 / 2 are connected by σ-bonds, the π-conjugation across the S = 1 and 1 / 2 moieties is substantially truncated. As a result, additional intramolecular exchange interactions through the σ-bonds in the resultant triradical are expected to be extremely small as compared with the ferromagnetic interaction in the S = 1 moiety.…”

Section: Introductionmentioning

confidence: 99%

“…In previous studies, − we designed and synthesized a triradical 1 (Figure ) from a phenol-substituted biradical 2 and a benzoic acid monoradical 3 as a building block of “single-component ferrimagnetics”. The phenol-based biradical 2 is known to have a triplet ( S = 1) ground state with the singlet−triplet energy gap of 2 J (π)/ k B = 26 K, which is retained in the triradical 1 after the esterification with 3 . ,, The amplitude of the additional interactions, | J (σ)| and | J ‘ (σ)|, of 1 has been estimated to be in the order of 100 mK from 14 N hyperfine splitting patterns of ESR spectra in a fluid solution 8,9 and magnetic susceptibility measurements in the ultra-low-temperature region down to 250 mK .…”

Section: Introductionmentioning

confidence: 99%

“…In previous studies, [8][9][10] we designed and synthesized a triradical 1 (Figure 2) from a phenol-substituted biradical 2 and a benzoic acid monoradical 3 as a building block of "singlecomponent ferrimagnetics". The phenol-based biradical 2 is known to have a triplet (S ) 1) ground state with the singlettriplet energy gap of 2J(π)/k B ) 26 K, 13 which is retained in the triradical 1 after the esterification with 3.…”

Section: Introductionmentioning

confidence: 99%

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Exchange Interaction in Covalently Bonded Biradical−Monoradical Composite Molecules

et al. 2005

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As a novel molecular designing for genuinely organic molecule-based ferrimagnets, we have proposed a strategy of "single-component ferrimagnetics". When a pi-biradical with an S = 1 ground state and a pi-monoradical with S = (1)/(2) are united by sigma-bonds, the pi-conjugation between the biradical and the monoradical moieties should be truncated in the resultant triradical. This gives magnetic degrees of freedom for both S = 1 and (1)/(2) in the single molecule, serving as a building block for organic molecule-based ferrimagnets under favorable conditions (single-component ferrimagnetics). We have designed and synthesized a triradical, 3-(1'-oxyl-3'-oxido-4',4',5',5'-tetramethylimidazolin-2-yl)benzoic acid 2,4-bis(1' '-oxyl-3' '-oxido-4' ',4' ',5' ',5' '-tetramethylimidazolin-2-yl)phenyl ester (4), as a model compound for the novel approach to genuinely organic ferrimagnets. In the triradical 4, a m-phenylene-bis(nitronyl nitroxide) biradical with a triplet (S = 1) ground state is united with a phenyl nitronyl nitroxide monoradical (S = (1)/(2)) by an ester coupler. Solution-phase ESR spectra from 4 exhibited a complex hyperfine splitting due to (14)N and (1)H nuclei. The analysis of the hyperfine structure based on perturbation calculations has revealed that the exchange interaction within the biradical moiety is much larger than those between the biradical and the monoradical moieties and the magnetic degrees of freedom for both S = 1 and (1)/(2) are retained in 4. An X-ray crystal structure analysis showed that the triradical molecules are arranged in a one-dimensional molecular chain in the crystal. The magnetic susceptibility in a crystalline solid state is consistent with the crystal structure.

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Molecular design of organic ferrimagnets

Cited by 15 publications

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Nature of the Ferromagnetic Behavior and Possible Occurrence of the Ferrimagnetic Phase Transition in Genuinely Organic Molecule-Based Assemblages with an S = 1 and S = ¹/ ₂ Antiferromagnetic Alternating Spin Chain: A Green’s Function Approach

Nature of the Ferromagnetic Behavior and Possible Occurrence of the Ferrimagnetic Phase Transition in Genuinely Organic Molecule-Based Assemblages with an S = 1 and S = ¹/ ₂ Antiferromagnetic Alternating Spin Chain: A Green’s Function Approach

Hyperfine structure of ESR spectra as a probe for heisenberg exchange couplings in nitroxide triradicals serving as building blocks for molecule-based ferrimagnets

Exchange Interaction in Covalently Bonded Biradical−Monoradical Composite Molecules

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Molecular design of organic ferrimagnets

Cited by 15 publications

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Nature of the Ferromagnetic Behavior and Possible Occurrence of the Ferrimagnetic Phase Transition in Genuinely Organic Molecule-Based Assemblages with an S = 1 and S = 1/ 2 Antiferromagnetic Alternating Spin Chain: A Green’s Function Approach

Nature of the Ferromagnetic Behavior and Possible Occurrence of the Ferrimagnetic Phase Transition in Genuinely Organic Molecule-Based Assemblages with an S = 1 and S = 1/ 2 Antiferromagnetic Alternating Spin Chain: A Green’s Function Approach

Hyperfine structure of ESR spectra as a probe for heisenberg exchange couplings in nitroxide triradicals serving as building blocks for molecule-based ferrimagnets

Exchange Interaction in Covalently Bonded Biradical−Monoradical Composite Molecules

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Product

Resources

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Nature of the Ferromagnetic Behavior and Possible Occurrence of the Ferrimagnetic Phase Transition in Genuinely Organic Molecule-Based Assemblages with an S = 1 and S = ¹/ ₂ Antiferromagnetic Alternating Spin Chain: A Green’s Function Approach

Nature of the Ferromagnetic Behavior and Possible Occurrence of the Ferrimagnetic Phase Transition in Genuinely Organic Molecule-Based Assemblages with an S = 1 and S = ¹/ ₂ Antiferromagnetic Alternating Spin Chain: A Green’s Function Approach