Simultaneous Control of Carriers and Localized Spins with Light in Organic Materials

Naito, T.; Karasudani, Tomoaki; Ohara, Kouzou; Takano, Takahiro; Takahashi, Yukihiro; Inabe, Tamotsu; Furukawa, Ko; Nakamura, Toshikazu

doi:10.1002/adma.201203153

Cited by 16 publications

(22 citation statements)

References 25 publications

(24 reference statements)

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“…They are practically isostructural, though the volume of unit cell doubles in the BPY salt compared to that of the MV salt. 122,123 The crystal structure of the BPY salt is shown in Figure 41. 122 The length of a-axis doubles, yet basic molecular arrangement in the MV salt is identical with that in the BPY salt.…”

Section: Secondmentioning

confidence: 99%

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Development of a Control Method for Conduction and Magnetism in Molecular Crystals

Naito

2016

Bulletin of the Chemical Society of Japan

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This study concerns development of a non-destructive method to control conduction and magnetism of molecular solids such as single crystals of charge-transfer complexes. The method is named “optical doping”, where appropriate irradiation is utilized under ambient conditions. Owing to this feature, it can be applied to a wide range of substances while measuring the properties during the control. In addition, the method adds unique conduction and magnetic properties to common insulators. Unlike other doping methods, optical doping only affects the properties and/or structures of the irradiated part of a sample while leaving the rest of the sample unchanged. There are two patterns in the optical doping. Irreversible optical doping produces junction-structures on the single molecular crystals, which exhibit characteristic behavior of semiconductor devices such as diodes and varistors. Reversible optical doping produces “giant photoconductors” and “photomagnetic conductors” by realizing unprecedented metallic photoconduction. In the latter case, localized spins are also excited to produce a Kondo system, where carriers and localized spins interact with each other. Not only the control of conduction and magnetism, the optical doping has realized the observation of physical properties in molecular crystals hardly observed under any thermodynamic condition.

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Section: Secondmentioning

confidence: 99%

“…122,123 Considering the crystal and the band structures, the conduction under dark conditions is governed by the unpaired electrons on the Ni(dmit) 2 anions. Both BPY and MV salts exhibited thermally activated behavior.…”

Section: Conduction and Magnetic Properties Under Dark Conditionsmentioning

confidence: 99%

Development of a Control Method for Conduction and Magnetism in Molecular Crystals

Naito

2016

Bulletin of the Chemical Society of Japan

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“…This implies that CT transition occurs between cations and anions under UV-irradiation. As the CT transitions between two different components in solids produce net photocarriers and photoexcited spins at the same time [10][11][12]16], the observed photoresponse in ESR spectra accounts for the observed photoresponse in electrical behavior mentioned above. The g-values of a part of the spins on the N atoms (#3 (N) in the dark conditon in Table A2 were markedly enhanced compared with those of isolated spins on the bipyridine derivatives (g~2.00 for N atoms), indicating strong interaction with the spins having larger g-values such as those in heavy atoms and transition metals, i.e., indicating strong interaction between cations and anions.…”

Section: Electron Spin Resonance (Esr)mentioning

confidence: 91%

“…Based on the discussion thus far, the overall relaxation time of photoexcited spins on the cations and anions is unusually prolonged to produce the observed photoresponse in ESR and conduction. Such prolonged relaxation times have been observed only in the CT complexes containing bipyridine derivatives with apparently mixed-stacking structures [10][11][12]. The mechanism can be related to the characteristic or advantage in this kind of molecular CT complexes such as CT interactions with photosensitive dyes, which would stabilize the photoexcited states.…”

Section: Structure-property Relationsmentioning

confidence: 99%

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Dye-Sensitized Molecular Charge Transfer Complexes: Magnetic and Conduction Properties in the Photoexcited States of Ni(dmit)2 Salts Containing Photosensitive Dyes

Yamamoto

Ohara

et al. 2017

Magnetochemistry

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Persistent Photomagnetism in Superparamagnetic Iron Oxide Nanoparticles

DuChene

Puretzky

et al. 2018

Adv Elect Materials

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phenomenon. [12][13][14][15] However, no experimental evidence was provided to exclude the light-induced photothermal effect and incontrovertibly demonstrate the existence of light-induced spin transitions in these metal-oxide systems. More importantly, it is noted that the photogenerated electrons in transition metal oxides are free to roam within the solid, [16,17] preventing them from directly altering the metal centers' spin configuration via localization on a single atomic site. This fundamental difference between material systems casts doubt over the validity of adopting the steady-state spin transition theory to describe photomagnetism in nanoparticlebased magnets.In this contribution, we examined the magnetic response of superparamagnetic Fe 3 O 4 nanoparticles following photoexcitation and found that the exciton-spin exchange-coupling interaction is the primary mechanism by which this archetypal transition metal oxide exhibits photomagnetism. Studying the photomagnetic response at temperatures below the blocking temperature under various external fields revealed that the exciton-spin exchange-coupling interaction reduces the magnetic energy barrier governing spin-flip transitions within iron oxide nanoparticles, allowing an optically driven magnetic phase transition from ferrimagnetic to superparamagnetic when held in their "blocked" state and a corresponding decrease in their saturation magnetization. Further investigation showed a significant decrease in photomagnetism as the Fe 3 O 4 nanoparticle size was increased, pinpointing the critical role of restricting the nanoparticle's magnetic anisotropy in enabling photomagnetism. Significantly, we have excluded light-induced photothermal heating as the source of photomagnetism in Fe 3 O 4 nanoparticles by comparing experimentally measured magnetization changes with those predicted from theoretical simulations based on a photothermal mechanism. Taken together, our findings provide fundamental insights into the origin of photomagnetism in transition metal oxides and establish a deeper understanding of the underlying mechanism that regulates the light-induced spin dynamics in iron oxide nanoparticles.High-resolution transmission electron microscopy (HRTEM) reveals that spherical nanoparticles were produced with an average size of 7.0 ± 1.0 nm (Figure 1a, also see Figure S1a,b in the Supporting Information). X-ray photoelectron spectroscopy Using light irradiation to manipulate magnetization over a prolonged period of time offers a wealth of opportunities for spin-based electronics and photonics. To date, persistent photomagnetism has been frequently reported in spin systems composed of molecular magnets; yet this phenomenon is rarely observed in nanoparticle-based systems comprised of transition metal oxides. Here, detailed studies of persistent photomagnetism in superparamagnetic iron oxide (Fe 3 O 4 ) nanoparticles at temperatures below their blocking temperature are presented and it is demonstrated that the magnetization change does not occur through stea...

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Simultaneous Control of Carriers and Localized Spins with Light in Organic Materials

Cited by 16 publications

References 25 publications

Development of a Control Method for Conduction and Magnetism in Molecular Crystals

Development of a Control Method for Conduction and Magnetism in Molecular Crystals

Dye-Sensitized Molecular Charge Transfer Complexes: Magnetic and Conduction Properties in the Photoexcited States of Ni(dmit)2 Salts Containing Photosensitive Dyes

Persistent Photomagnetism in Superparamagnetic Iron Oxide Nanoparticles

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