Hyperfine interaction and its effects on spin dynamics in organic solids

Yu, Zhi; Ding, Fazhu; Wang, Haobin

doi:10.1103/physrevb.87.205446

Cited by 42 publications

(52 citation statements)

References 31 publications

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“…According to HFI-induced spin relaxation, the spin diffusion length depends on magnetic field [10], resulting in the curvature of resistance around zero field. The sharper switching suggests smaller HFI strength, in agreement with the theoretical calculation that the HFI in Ir (ppy) 3 is smaller than in Alq 3 by roughly a factor of two [39]. Considering that the SOC strength is low in both molecules in spin transport, this feather suggests the HFI is the dominant spin relaxation mechanism in these two molecules.…”

Section: Discussionsupporting

confidence: 86%

“…Indeed, the effective HFI field of these two molecules was estimated to be about 50 Oe from OMAR measurements [17]. Moreover, a recent theoretical calculation shows that the effective HFI field is 4.1-8.7 Oe in Ir(ppy) 3 and 12.2-12.4 Oe in Alq 3 , and which varies due to the different carrier type and the detailed molecular structures [39]. Both the experimental measurements and theoretical calculations reveal that the effective HFI field in Alq 3 and Ir(ppy) 3 is comparable and well below 100 Oe.…”

Section: Discussionmentioning

confidence: 99%

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The role of heavy metal ions on spin transport in organic semiconductors

et al. 2015

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It is generally believed that spin-orbit coupling (SOC) strength and the associated spin relaxation can be enhanced by introducing heavy metal ions in organic semiconductors. Here, we systematically study the spin transport in two organic semiconductors, tris(2-phenylpyridine)iridium (Ir(ppy) 3 ) and tris-(8-hydroxyquinoline) aluminum (Alq 3 ), which have similar chemical structures except that Ir(ppy) 3 contains a heavy metal ion Ir. As expected, the photoluminescence spectroscopy measurements show that the SOC strength in Ir(ppy) 3 is several orders of magnitude larger than in Alq 3 . Surprisingly, the spin diffusion length in Ir(ppy) 3 , deduced from magnetoresistance measurements in Ir (ppy) 3 -based organic spin valves, is longer than in Alq 3 . Considering the lower carrier mobility in Ir (ppy) 3 , the spin relaxation time in Ir(ppy) 3 is much longer than in Alq 3 , implying that the SOC strength in Ir(ppy) 3 is weaker than in Alq 3 . The seemingly contradictory results of photoluminescence spectroscopy and magneto-transport can be explained by the SOC strength depending on the electronic states of a material. The weak SOC strength in Ir(ppy) 3 observed in magneto-transport measurements is due to the strong ligand field induced orbital moment quenching for Ir 3+ and the polarons transporting in the ligands. However, the excitons involved in photoluminescence spectroscopy overlap with the Ir ion and transforms Ir 3+ to Ir 4+ , which has non-zero spin and orbital moments and hence results in high SOC strength.

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Section: Discussionsupporting

confidence: 86%

Section: Discussionmentioning

confidence: 99%

The role of heavy metal ions on spin transport in organic semiconductors

et al. 2015

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“…In general, the spin polarization of the transport electrons in the OSCs is attenuated exponentially as e –d/λ S when electrons diffuse across the organic spacer with the thickness, d . Here, λ S is the spin diffusion length of the carriers in the organic spacer that in general depends on the mobility, μ , and the spin relaxation time, τ , of the transport electron following the relation,

λ_{S} = \sqrt{μ k_{B} T τ / e}

where k B , T , and e are the Boltzmann constant, the material temperature, and the carrier charge, respectively . In principle, the MR response of a device can be tuned by manipulating the spin relaxation time in its semiconducting spacer.…”

Section: Fundamental Conceptsmentioning

confidence: 99%

Organic Spin Valves: A Review

Devkota

Geng

Subedi

et al. 2016

Adv Funct Materials

108

106

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accelerated impressively and advanced to a range of materials and a number of techniques to verify the successful injection and transport of the SP carriers. [ 1,2,10,11 ] The effect has been realized in a variety of materials combinations such as FM fi lms, FM/anti-FM coupled layers, or FM semiconductors as the injection/detection electrodes and the metals, superconductors, inorganic semiconductors, organic semiconductors, and insulators including ferroelectric and topological insulators as the spacers. [ 1,2,[12][13][14][15][16][17][18] The GMR effect was extensively studied using non-magnetic metallic interlayer and its applications such as electric switching, magnetic recording, and sensors were suggested and employed. [ 1,2,16 ] However, all-metallic spintronic devices imposed restrictions in applications as they are characterized by short spin relaxation time (≈picosecond) and are not suitable for coherent spin manipulation. [ 1,2,19 ] To overcome these limitations, the spintronics community caught its attention towards hybrid devices with semiconductors (SCs) sandwiched in between the FM layers and continued advancing to a range of semiconducting materials. [ 2,14,[20][21][22] The organic semiconductors (OSCs) are among the youngest members of the spacer materials and were fi rst tested in the spintronic devices only about a decade ago. Nevertheless, OSC devices have been of continuously advancing research topics over the past three decades for their rich physics, fl exible chemi stry, cost effi ciency, and potential applications in new generations of electronic devices including organic light emitting diodes (OLEDs), [23][24][25] organic solar cells, [ 26,27 ] and organic fi eld effect transistor. [ 28,29 ] In fact, OLEDs have already revolutionized the modern display industry and spin-dependent devices such as organic spin valves (OSVs), OLED-based magnetic sensors, and spin-OLEDs are under intensive study to achieve their new avenues. [30][31][32] This increasing interest on organic electronics is for their several distinctions over inorganic counterparts. [19][20][21]33,34 ] Electronically, the band theory explains the electric transport in inorganic SCs while charge hopping is the main transport mechanism in the OSCs with much smaller carrier mobility. This is a favorable condition for large electron-hole pair recombination without the need of using a p-n junction structure. [23][24][25] Spintronically, the inorganic SCs contain heavy atoms giving rise to a large spin-orbit coupling (SOC), which is a response of the electron spin degree of freedom to its orbital environment. The strength of the SOC in solids depends upon the nature of orbital wave functions of electrons and the materials structure. [ 35 ] In case of hydrogenic wave-function-like electrons (s-orbital electrons), it is Organic spintronics is an emerging and potential platform for future electronic devices. Signifi cant progress has been made in understanding the spin injection, manipulation, and detection in organic spin valves in the p...

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“…In addition, previous studies for spin relaxation times in organic materials typically use an indirect method via estimation linewidths by continuous wave (cw) electron spin resonance (ESR) spectroscopy, which introduces several approximations. Compared with deuteration modification, [24] chlorination is more easily accessible and has been widely used for tuning the electronic properties of OSCs. [16,17] The triphenylmethyl (TM) radical and its derivatives have already been used as building blocks for conductor in spintronics [18,19] and semiconducting materials for organic lightemitting diodes.…”

mentioning

confidence: 99%

Chemical Modification toward Long Spin Lifetimes in Organic Conjugated Radicals

et al. 2018

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Organic semiconductors for spin-based devices require long spin relaxation times. Understanding their spin relaxation mechanisms is critical to organic spintronic devices and applications for quantum information processing. However, reports on the spin relaxation mechanisms of organic conjugated molecules are rare and the research methods are also limited. Herein, we study the molecular design and spin relaxation mechanisms by systematically varying the structure of a conjugated radical. We found that solid-state relaxation times of organic materials are largely different from that in solution state. We demonstrate that substitution of a lower gyromagnetic ratio nucleus (e. g. D, Cl) on the para-position of the aryl rings in the triphenylmethyl (TM) radical can significantly improve their coherence times (T ). Flexible thin films based on such radicals exhibit ultra-long spin-lattice relaxation times (T ) up to 35.6(6) μs and T up to 1.08(4) μs under ambient conditions, which are among the longest values in films. More importantly, using the TM radical derivative (5CM), we observed room-temperature quantum coherence and Rabi cycles in thin film for the first time, suggesting that organic conjugated radicals have great potentials for spin-based information processing.

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Hyperfine interaction and its effects on spin dynamics in organic solids

Cited by 42 publications

References 31 publications

The role of heavy metal ions on spin transport in organic semiconductors

The role of heavy metal ions on spin transport in organic semiconductors

Organic Spin Valves: A Review

Chemical Modification toward Long Spin Lifetimes in Organic Conjugated Radicals

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