Showing papers by "Valentin Dediu published in 2018"
TL;DR: Variable oxygen doping of the organic molecules represents the key element for correlating bistability and MR, and the measurements provide the first experimental evidence in favor of the impurity-driven model describing the spin transport in organic semiconductors in similar devices.
Abstract: Vertical crossbar devices based on manganite and cobalt injecting electrodes and a metal-quinoline molecular transport layer are known to manifest both magnetoresistance (MR) and electrical bistability. The two effects are strongly interwoven, inspiring new device applications such as electrical control of the MR and magnetic modulation of bistability. To explain the device functionality, we identify the mechanism responsible for electrical switching by associating the electrical conductivity and the impedance behavior with the chemical states of buried layers obtained by in operando photoelectron spectroscopy. These measurements revealed that a significant fraction of oxygen ions migrate under voltage application, resulting in a modification of the electronic properties of the organic material and of the oxidation state of the interfacial layer with the ferromagnetic contacts. Variable oxygen doping of the organic molecules represents the key element for correlating bistability and MR, and our measurements provide the first experimental evidence in favor of the impurity-driven model describing the spin transport in organic semiconductors in similar devices.
21 citations
TL;DR: In this paper, the authors investigated the transport properties of a large number of tris-(8-hydroxyquinoline)aluminum-based organic spintronic devices with an electrical resistance greater than 5 MΩ that did not show magnetoresistance.
Abstract: The understanding of spin injection and transport in organic spintronic devices is still incomplete, with some experiments showing magnetoresistance and others not detecting it. We have investigated the transport properties of a large number of tris-(8-hydroxyquinoline)aluminum-based organic spintronic devices with an electrical resistance greater than 5 MΩ that did not show magnetoresistance. Their transport properties could be described satisfactorily by known models for organic semiconductors. At high voltages (>2 V), the results followed the model of space charge limited current with a Poole-Frenkel mobility. At low voltages (∼0.1 V), that are those at which the spin valve behavior is usually observed, the charge transport was modelled by nearest neighbor hopping in intra-gap impurity levels, with a charge carrier density of n0 = (1.44 ± 0.21) × 1015 cm−3 at room temperature. Such a low carrier density can explain why no magnetoresistance was observed.
9 citations
TL;DR: In this paper, an element-specific investigation of the electronic and magnetic structures of Fe/TNAP system by use of near edge X-Ray absorption fine structure (NEXAFS) and X-ray magnetic circular dichroism (XMCD) is reported.
Abstract: Spinterface engineering has shown quite important roles in organic spintronics as it can improve spin injection or extraction. In this study, 11,11,12,12‐tetracyanonaptho‐2,6‐quinodimethane (TNAP) is introduced as an interfacial layer for a prototype interface of Fe/TNAP. An element‐specific investigation of the electronic and magnetic structures of Fe/TNAP system by use of near edge X‐Ray absorption fine structure (NEXAFS) and X‐ray magnetic circular dichroism (XMCD) is reported. Strong hybridization between TNAP and Fe and induced magnetization of N atoms in TNAP molecule are observed. XMCD sum rule analysis demonstrates that the adsorption of TNAP reduces the spin moment of Fe by 12%. In addition, induced magnetization in N K‐edge of TNAP is also found with other commonly used ferromagnets in organic spintronics, such as La0.7Sr0.3MnO3 and permalloy, which makes TNAP a very promising molecule for spinterface engineering in organic spintronics.
5 citations
TL;DR: In this paper, the magnetic and magnetotransport properties of Ni80Fe20/La0.7Sr0.3MnO3 bilayers were investigated after bombarding the LSMO surface with low-energy Ar+ or O2+/Ar+ ion beams before the growth of the top NiFe layer.
Abstract: The magnetic and magnetotransport properties of Ni80Fe20/La0.7Sr0.3MnO3 (NiFe/LSMO) bilayers were investigated after bombarding the LSMO surface with low-energy Ar+ or O2+/Ar+ ion beams before the growth of the top NiFe layer. A variety of magnetic properties are revealed, including an asymmetric two-stepped hysteresis loop with an exchange bias loop shift, and alternatively, a symmetric two-stepped hysteresis loop with an enhanced coercivity. Polarized neutron reflectometry measurements provide details of the magnetic depth profile and interface layer magnetism at different temperatures. The LSMO surface modifications determine a complex magnetic and electric NiFe/LSMO interface having a strong effect on the magnetoresistance of the bilayer. Surface engineering based on ion beam bombardment is presented as a promising technique for optimizing the electronic and magnetic properties of NiFe/LSMO junctions for future device applications.
4 citations
Posted Content•
TL;DR: In this paper, an element-specific investigation of the electronic and magnetic structures of Fe/TNAP system by use of near edge X-Ray absorption fine structure (NEXAFS) and X-ray magnetic circular dichroism (XMCD) was performed.
Abstract: Spinterface engineering has shown quite important roles in organic spintronics as it can improve spin injection or extraction. In this study, 11,11,12,12-tetracyanonaptho-2,6-quinodimethane (TNAP) is introduced as an interfacial layer for a prototype interface of Fe/TNAP. We report an element-specific investigation of the electronic and magnetic structures of Fe/TNAP system by use of near edge X-Ray absorption fine structure (NEXAFS) and X-ray magnetic circular dichroism (XMCD). Strong hybridization between TNAP and Fe and induced magnetization of N atoms in TNAP molecule are observed. XMCD sum rule analysis demonstrates that the adsorption of TNAP reduces the spin moment of Fe by 12%. In addition, induced magnetization in N K-edge of TNAP has also been found with other commonly used ferromagnets in organic spintronics, such as La0.7Sr0.3MnO3 and permalloy, which makes TNAP a very promising molecule for spinterface engineering in organic spintronics.
1 citations