Direct imaging and spectral identification of the interfaces in organic semiconductor-ferromagnet heterojunction

Wei, Der-Hsin; Wang, Chia-Hao; Chang, Hwan‐You; Chan, Yuet-Loy; Lee, Chih‐Hao; Hsu, Yao-Jane

doi:10.1063/1.4756943

Cited by 9 publications

(3 citation statements)

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“…4(a), implying that no significant long-range order was formed to create a FM ordering near 295 K. This result is ascribed to the exchange energy necessary to align the spins of diffused and hybridized Co nanoparticles being smaller than the thermal fluctuation that tends to diminish the weak magnetic dipole-dipole interactions produced by the individual spins. A retarded FM property of Co in doping with organic molecules was found [35][36]; an insufficiently metallic Co could hence be another reason to explain the suppression of magnetization found in the Co XMCD. To clarify the origin of the loss of ferromagnetism of Co near 295 K, we examined the FM properties of 3.5 ML Co on Alq3 at 79 K. Through the Co XMCD for a sample cooled to 79 K, we observed a XMCD signal, displayed in Fig.…”

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“…Zhan eta l. demonstrated an induced SP through hybridiza tion and exchange coupling at the interface of Alq3 adsorbed on Fe [29]; Steil et al discovered that the hybrid states at the interface of Alq3 adsorbed on Co at which electrons are trapped act as spin filters [32]. The interfacial SP role at the top contact of a FM atop an OSC is, however, still unknown and more complicated because penetration, diffusion, and reaction of a metal occur at the ill-defined interface [13,[34][35][36]. In the worst case, for a fragile OSC, the reaction might modify or damage the molecular structures and yield degraded electronic and magnetic properties [37], Only a MR response is hence mea sured for fragile organic molecules in a planar-type OSV [38], The situation might differ completely if the molecules contain an appropriate functional group that can resist degradation and become spin polarized.…”

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Effectiveness of organic molecules for spin filtering in an organic spin valve: Reaction-induced spin polarization for Co atopAlq3

et al. 2015

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The spin polarization of organic-ferromagnetic interfaces in an organic spin valve critically affects the efficiency of spin injection or detection. We examined the chemical and electronic properties of ferromagnetic Co deposited on organic Alq3 and the interfacial spin-polarized capability of the electronic states. Our x-ray photoemission spectra and calculations with density-functional theory indicate a sequential and unequal distribution of charge from Co clusters to N and then to O atoms in Alq3. The preferential orbital hybridization at specific functional sites produces efficient spin polarization of organic molecules. Element-specific measurements of x-ray magnetic circular dichroism demonstrate the preferential spin polarization in the lowest unoccupied molecular orbital state of N atoms at the complex interface for Co atop Alq3, which agrees satisfactorily with calculation. Our results indicate that an induced interfacial spin polarization on engineering the dominant reaction of Co with mainly N and O atoms in Alq3 might pave a way for effective spin filtering in organic spintronics.PACS number(s): 79.60. Fr, 75.70.Cn, 68.35.Fx, 75.76.+j Organic spin valves (OSV) in which an organic semicon ductor (OSC) spacer is sandwiched between two ferromagnetic (FM) electrodes have attracted much attention because of an enduring spin coherence of organic materials via weak spin-orbit coupling [1], Dediu et al. pioneered in achiev ing magnetoresistance (MR) up to 30% near 295 K in a LaovSrojMnOsfLSMOj/sexithiophenefTgj/LSMO OSV, ini tiating a great potential of organic-based spintronics [2], Xiong et al. subsequently made a remarkable observation of a giant MR at 40% at 11 K in a LSMO/Alq3/CoOSV [1], Among the most widely used OSC in OSV, tri(8-hydroxyquinoline) aluminum (Alq3) composed of 7r-conjugated molecules is considered to be a promising material for effective spin transport because of its great spin-relaxation time and unique molecular structure [1,3-6], The combination of Alq3 and d -band FM Co has achieved striking MR values [1,7-12], Although an ill-defined layer between Alq3 and top Co was manifested at an Alq3 thickness greater than 100 nm, it is one of few examples in which an OSV displayed a large MR [1], Such an ill-defined layer is ascribed to the diffusion of metal into a soft organic layer, which might be related to the disputed results of the MR sign and mechanism [1,12-15], To prevent the unexpected interdiffusion and chemical interaction at the interfacial region, a buffer layer inserted between the top Co and Alq3 has improved the device performance [9,16-18]. Although metal interdiffusion is preventable with those meth ods, it might not provide a deep understanding of the lacking essential mechanisms [19][20][21]. Moreover, in the case of an OSV with no buffer layer, a large MR was still achieved [1,8]. Various techniques have been used to engineer, to control, or to detect the efficient spin injection and transport [ 1,4,22,23] 'jenghan @ on traditionally applying a specific bias voltage to...

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Effectiveness of organic molecules for spin filtering in an organic spin valve: Reaction-induced spin polarization for Co atopAlq3

et al. 2015

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“…Diffusion of metal atoms into the organic film may then assist the formation of metallic filaments. Such diffusion effects are well known in the organic electronics community, and have been addressed as well in the context of organic spintronic devices [61][62][63][64].…”

Section: Organic Spin Valves With "Thick" Organic Spacersmentioning

confidence: 99%

Recent progress in organic spintronics

Jong

2016

Open Physics

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Abstract:The field of organic spintronics deals with spin dependent phenomena occurring in organic semiconductors or hybrid inorganic/organic systems that may be exploited for future electronic applications. This includes magnetic field effects on charge transport and luminescence in organic semiconductors, spin valve action in devices comprising organic spacers, and magnetic effects that are unique to hybrid interfaces between (ferromagnetic) metals and organic molecules. A brief overview of the current state of affairs in the field is presented.

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Magnetic Imaging

Bauer

2014

Surface Microscopy With Low Energy Electrons

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Direct imaging and spectral identification of the interfaces in organic semiconductor-ferromagnet heterojunction

Cited by 9 publications

References 31 publications

Effectiveness of organic molecules for spin filtering in an organic spin valve: Reaction-induced spin polarization for Co atopAlq3

Effectiveness of organic molecules for spin filtering in an organic spin valve: Reaction-induced spin polarization for Co atopAlq3

Recent progress in organic spintronics

Magnetic Imaging

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