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Electrical generation and transduction of polarized electron spins in semiconductors (SCs) are of central interest in spintronics and quantum information science. While spin generation in SCs is frequently realized via electrical injection from a ferromagnet (FM), there are significant advantages in nonmagnetic pathways of creating spin polarization. One such pathway exploits the interplay of electron spin with chirality in electronic structures or real space. Here, utilizing chirality-induced spin selectivity (CISS), the efficient creation of spin accumulation in n-doped GaAs via electric current injection from a normal metal (Au) electrode through a self-assembled monolayer (SAM) of chiral molecules (α-helix l-polyalanine, AHPA-L), is demonstrated. The resulting spin polarization is detected as a Hanle effect in the n-GaAs, which is found to obey a distinct universal scaling with temperature and bias current consistent with chirality-induced spin accumulation. The experiment constitutes a definitive observation of CISS in a fully nonmagnetic device structure and demonstration of its ability to generate spin accumulation in a conventional SC. The results thus place key constraints on the physical mechanism of CISS and present a new scheme for magnet-free SC spintronics.

Spin-crossover (SCO) and single-ion magnets (SIMs), or their mixed SCO-SIM derivatives, are a convenient solution in the evolution from molecular magnetism toward molecular spintronics and quantum computing. Herein, we report on the current trends and future directions on the use of mononuclear six-coordinate CoII SCO-SIM complexes with potential opto-, electro-, or chemo-active 2,6-pyridinediimine (PDI)- and 2,2′:6′,2′-terpyridine (TERPY)-type ligands as archetypical examples of multifunctional and multiresponsive magnetic devices for applications in molecular spintronics and quantum computing technologies. This unique class of spin-crossover cobalt(II) molecular nanomagnets is particularly well suited for addressing and scaling on different supports, like metal molecular junctions or carbon nanomaterials (CNMs) and metal–organic frameworks (MOFs) or metal-covalent organic frameworks (MCOFs), in order to measure the single-molecule electron transport and quantum coherence properties, which are two major challenges in single-molecule spintronics (SMS) and quantum information processing (QIP). [ABSTRACT FROM AUTHOR]

Compared with aggregate spin behavior, single‐molecule spin behavior can be accurately understood, controlled, and applied at the level of basic building blocks. The potential of single‐molecule electronic and nuclear spins for monitoring and control represents a beacon of promise for the advancement of molecular spin devices, which are fabricated by connecting a single molecule between two electrodes. Metal complexes, celebrated for their superior magnetic attributes, are widely used in the devices to explore spin effects. Moreover, single‐molecule electrical techniques with high signal‐to‐noise ratio, temporal resolution, and reliability help to understand the spin characteristics. In this review, the focus is on the devices with metal complexes, especially single‐molecule magnets, and systematically present experimental and theoretical state of the art of this field at the single‐molecule level, including the fundamental concepts of the electronic and nuclear spin and their basic spin effects. Then, several experimental methods developed to regulate the spin characteristics of metal complexes at single‐molecule level are introduced, as well as the corresponding intrinsic mechanisms. A brief discussion is provided on the comprehensive applications and the considerable challenges of single‐molecule spin devices in detail, along with a prospect on the potential future directions of this field. [ABSTRACT FROM AUTHOR]

The development of neuromorphic devices is a pivotal step in the pursuit of low‐power artificial intelligence. A synaptic analog is one of the building blocks of this vision. The synaptic behavior of molecular La0.7Sr0.3MnO3/tris(8‐hydroxyquinolinato)gallium/AlOx/Co spintronic devices is studied, where the conductance plays the role of the synaptic weight. These devices are arranged in a crossbar configuration, the most effective architecture for the purpose. The conductance of each cross point is controlled separately by the application of voltage pulses: when set in the high conductance potentiated state, the devices show a spin‐valve magnetoresistance, while in the low conductance depressed state, no magnetoresistance is observed. The time dependence of the resistive switching behavior is an important parameter of the synaptic behavior and is very revealing of the underlying physical mechanisms. To study the time dynamics of the resistive switching after the voltage pulses, the response of the device to trains of potentiation and depression pulses, and the time‐resolved conductivity relaxation after the pulses are measured. The results are described with the conductivity model based on impurity energy levels in the organic semiconductor's gap. A flat distribution of the activation energies necessary to move these impurities is hypothesized, which can explain the observed glassy behavior. [ABSTRACT FROM AUTHOR]

Molecular semiconductors (MSCs) are known as ideal candidates for constructing room‐temperature spin‐charge interactive devices due to their long spin lifetimes and abundant photoelectric properties. These devices can achieve novel and valuable functionalities such as room‐temperature supply units of fully spin‐polarized current. Unfortunately, their performances (sub‐0.1 nA) remain unsatisfactory due to limited charge and spin injection efficiency, which can hardly be improved despite great efforts thus far. Herein, from the theoretical side, an interfacial tunnel layer with precisely‐controlled barrier in spintronic devices may simultaneously enhance spin and charge injection. Accordingly, a solution‐processed small molecule with smooth morphology and amorphous structure is introduced to form a uniform and well‐controllable barrier in molecular spin‐photovoltaic devices. By modulating the thickness to effectively control the barrier, both spin and charge injection efficiency increase by > 150%. Thus, the spin‐charge interactive functionalities as supply units of fully spin‐polarized current have also been significantly improved than the current record at room temperature, the output fully spin‐polarized current (>2 nA) is 1200%‐larger, and the output power increases by > 50 times. Moreover, the interface‐modified spintronic devices exhibit excellent stability even after 70 days of exposure to air, which is essential for practical applications in the future. [ABSTRACT FROM AUTHOR]

Abstract The development of neuromorphic devices is a pivotal step in the pursuit of low‐power artificial intelligence. A synaptic analog is one of the building blocks of this vision. The synaptic behavior of molecular La0.7Sr0.3MnO3/tris(8‐hydroxyquinolinato)gallium/AlOx/Co spintronic devices is studied, where the conductance plays the role of the synaptic weight. These devices are arranged in a crossbar configuration, the most effective architecture for the purpose. The conductance of each cross point is controlled separately by the application of voltage pulses: when set in the high conductance potentiated state, the devices show a spin‐valve magnetoresistance, while in the low conductance depressed state, no magnetoresistance is observed. The time dependence of the resistive switching behavior is an important parameter of the synaptic behavior and is very revealing of the underlying physical mechanisms. To study the time dynamics of the resistive switching after the voltage pulses, the response of the device to trains of potentiation and depression pulses, and the time‐resolved conductivity relaxation after the pulses are measured. The results are described with the conductivity model based on impurity energy levels in the organic semiconductor's gap. A flat distribution of the activation energies necessary to move these impurities is hypothesized, which can explain the observed glassy behavior.

Molecular semiconductors (MSCs), characterized by a longer spin lifetime than most of other materials due to their weak spin relaxation mechanisms, especially at room temperature, together with their abundant chemical tailorability and flexibility, are regarded as promising candidates for spintronic applications. Molecular spintronics, as an emerging subject that utilizes the unique properties of MSCs to study spin-dependent phenomena and properties, has attracted wide attention. In molecular spintronic devices, MSCs play the role as medium for information transport, process, and storage, in which the efficient spin inject–transport process is the prerequisite. Herein, we focus mainly on summarizing and discussing the recent advances in theoretical principles towards spin transport of MSCs in terms of the injection of spin-polarized carriers through the ferromagnetic metal/MSC interface and the subsequent transport within the MSC layer. Based on the theoretical progress, we cautiously present targeted design strategies of MSCs that contribute to the optimization of spin-transport efficiency and give favorable approaches to exploring accessional possibilities of spintronic materials. Finally, challenges and prospects regarding current spin transport are also presented, aiming to promote the development and application of the rosy and energetic field of molecular spintronics. [ABSTRACT FROM AUTHOR]

Spin-dependent and enantioselective electron-molecule scattering occurs in photoelectron transmission through chiral molecular films. This spin selectivity leads to electron spin filtering by molecular helices, with increasing magnitude concomitant with increasing numbers of helical turns. Using ultraviolet photoelectron spectroscopy, we measured spin-selective surface charging accompanying photoemission from ferromagnetic substrates functionalized with monolayers of mercurated DNA hairpins that constitute only one helical turn. Mercury ions bind specifically at thymine-thymine mismatches within self-hybridized single-stranded DNA, enabling precise control over the number and position of Hg2+ along the helical axis. Differential charging of the organic layers, manifested as substrate-magnetization-dependent photoionization energies, was observed for DNA hairpins containing Hg2+; no differences were measured for hairpin monolayers in the absence of Hg2+. Inversion of the DNA helical secondary structure at increased metal loading led to complementary inversion in spin selectivity. We attribute these results to increased scattering probabilities from relativistic enhancement of spin-orbit interactions in mercurated DNA.

The long‐term future of information storage requires the use of sustainable nanomaterials in architectures operating at high frequencies. Interfaces can play a key role in this pursuit via emergent functionalities that break out from conventional operation methods. Here, spin‐filtering effects and photocurrents are combined at metal‐molecular‐oxide junctions in a hybrid magneto‐capacitive memory. Light exposure of metal‐fullerene‐metal oxide devices results in spin‐polarized charge trapping and the formation of a magnetic interface. Because the magnetism is generated by a photocurrent, the writing time is determined by exciton formation and splitting, electron hopping, and spin‐dependent trapping. Transient absorption spectroscopy measurements show changes in the electronic states as a function of the magnetic history of the device within picoseconds of the optical pumping. The stored information is read using time‐resolved scanning magneto optic Kerr effect measurements during microwave irradiation. The emergence of a magnetic interface in the picosecond timescale opens new paths of research to design hybrid magneto‐optic structures operating at high frequencies for sensing, computing, and information storage. [ABSTRACT FROM AUTHOR]

The possibility of preparing thin films of cobalt(II) cage complex (clathrochelate) that undergoes a temperature-induced spin transition by thermal sublimation was demonstrated using UV spectroscopy. The films were more uniform and more thermally stable than the films formed by centrifugation of the solution on a substrate surface. In combination with scanning electron microscopy data, this revealed the dependence of the spin transition temperature on the method of film preparation and dependence of the supramolecular organization in the films on the substrate material, indicating that transition metal clathrochelates show the spinterface effect at the interface with a metal electrode. In addition to the possibility of controlling the magnetic properties of this unique class of coordination compounds by molecular design methods, this effect opens up broad opportunities for creating molecular spintronic devices with characteristics tailored for the researcher requirements. [ABSTRACT FROM AUTHOR]

A collinear antiferromagnetic molecular wire with zero total magnetic moments based on 1,3-diphenylpropynylidene radicals was sandwiched between two nonmagnetic Al leads. The transport characteristics with spin-polarization for this molecular junction were performed using an first-principles method based on density functional theory combined with non-equilibrium Green's functions. Reversible and high spin polarization was obtained in this collinear antiferromagnetic molecular wire, which was originated from that the bias voltage broke the symmetry of spin sublattices. Especially, the sign of spin polarization could be adjusted by changing the bias. Our calculations greatly contribute for developing novel antiferromagnetic spintronics devices with single molecular scale. [ABSTRACT FROM AUTHOR]

Spintronics, being one of the youngest fields of microelectronics, is applied already for several decades to enhance the efficiency of components of computer equipment and to develop units of quantum computer and other electronic devices. The use of molecular material layers in a spintronic device makes it possible to substantially deepen the understanding of the spin transport mechanisms and to form foundation for a new trend at the nexus of physics and chemistry: molecular spintronics. Since the appearance of this trend, various coordination compounds, including semiconductors, single-molecule magnets, complexes with spin transitions, and metal-organic frameworks, are considered as molecular materials of spintronic devices with diverse unusual characteristics imparted by these materials. Specific features of using the earlier described representatives of the listed classes of compounds or their analogs, which are still "kept on the shelves" in chemical laboratories, for manufacturing polyfunctional devices of molecular spintronics are briefly reviewed. [ABSTRACT FROM AUTHOR]

Organic semiconductors, characterized by their exceptionally long spin relaxation times (≈ms) and unique spinterface effects, are considered game-changers in spintronics. However, achieving high-performance and wide-range tunable magnetoresistance (MR) in organic spintronic devices remains challenging, severely limiting the development of organic spintronics. This work combines straintronic multiferroic heterostructures with organic spin valve (OSV) to develop a three-terminal OSV device with a gate structure. The device exhibits a record-high MR ratio of 281% which 10 times higher than the average in polymer systems. More importantly, this work can perform multilevel writing operations on the device using gate voltages and create at least 10 stable spin-dependent working states within a single device. Both experiments and theoretical calculations confirm such an extraordinary tunability range originates from the synergistic effects of strain and charge accumulation that amplified by the spinterface. This study demonstrates the potential of OSV systems for efficient spin manipulation and highlights the spinterface as an ideal platform for amplifying spin effects for next-generation spintronic devices., (© 2024 Wiley‐VCH GmbH.)

Abstract A new type of spin-current filter is proposed that consists of a single-molecule magnet (SMM) coupled to two normal metal electrodes. It is shown that this tunneling junction can generate a highly spin-polarized current, whose spin polarization can be switched by means of magnetic fields and gate voltages applied to the SMM. This spin switching in the SMM tunnel junction arises from spin-selective single-electron resonant tunneling via the lowest unoccupied molecular orbit of the SMM. The electron current spectrum is still spin polarized in the absence of an external magnetic field, which can help to judge whether the molecule’s spin state has reached the ground-state doublet $$|\pm S\rangle$$ | ± S ⟩ . This device can be realized with current technologies and may have practical use in spintronics and quantum information.

Functional molecules and their assemblies have attracted considerable attention arising from not only diverse structures with novel properties but also potential applications in molecular devices. The novel properties, which determine their applications, are strongly related to their structures. In recent years, benefiting from the development of atomically precise control technique of the structures, a lot of new materials constructing from molecules with novel properties emerged. Their novel properties enable them to be potentially applied in molecular spintronics, high‐density data storage, selective reaction and quantum topological devices, and so on. The present review focuses on new progress in predicting and controlling the structures and properties of functional molecules and their assemblies on metal surfaces by combining first‐principle calculations with scanning tunneling microscopy experiments. We aim at understanding the key factors which affect the physical and chemical properties of the metal–organic systems, especially from a theoretical perspective. This article is categorized under:Structure and Mechanism > Molecular StructuresElectronic Structure Theory > Density Functional Theory [ABSTRACT FROM AUTHOR]

Electrical generation and transduction of polarized electron spins in semiconductors (SCs) are of central interest in spintronics and quantum information science. While spin generation in SCs is frequently realized via electrical injection from a ferromagnet (FM), there are significant advantages in nonmagnetic pathways of creating spin polarization. One such pathway exploits the interplay of electron spin with chirality in electronic structures or real space. Here, utilizing chirality-induced spin selectivity (CISS), the efficient creation of spin accumulation in n-doped GaAs via electric current injection from a normal metal (Au) electrode through a self-assembled monolayer (SAM) of chiral molecules (α-helix l-polyalanine, AHPA-L), is demonstrated. The resulting spin polarization is detected as a Hanle effect in the n-GaAs, which is found to obey a distinct universal scaling with temperature and bias current consistent with chirality-induced spin accumulation. The experiment constitutes a definitive observation of CISS in a fully nonmagnetic device structure and demonstration of its ability to generate spin accumulation in a conventional SC. The results thus place key constraints on the physical mechanism of CISS and present a new scheme for magnet-free SC spintronics., (© 2024 Wiley‐VCH GmbH.)

Manipulating individual molecular spin states with electronic current has the potential to revolutionize quantum information devices. However, it is still unclear how a current can cause a spin transition in single-molecule devices. Here, we propose a spin-crossover (SCO) mechanism induced by electron-phonon coupling in an iron(II) phthalocyanine molecule situated on a graphene-decoupled Ir(111) substrate. We performed simulations of both elastic and inelastic electron tunneling spectroscopy (IETS), which reveal current-induced Fe-N vibrations and an underestimation of established electron-vibration signals. Going beyond standard perturbation theory, we examined molecules in various charge and spin states using the Franck-Condon framework. The increased probability of spin switching suggests that notable IETS signals indicate SCO triggered by the inelastic vibrational excitation associated with Fe-N stretching.

The thermal sublimation of the known cage iron(II) complex (clathrochelate) gives thin films of this compound on various supports without violating its integrity as shown by electron spectroscopy. The spin state of the complex remains unchanged compared to the polycrystalline sample and solution. The first prototypes of molecular spintronic devices in the form of a vertical spin valve are prepared from the chosen iron(II) clathrochelate, and their electron transport properties are studied. [ABSTRACT FROM AUTHOR]

Organic spin valve (OSV), one of the most promising and representative devices involving spin injection, transport and detection, has drawn tremendous attention owing to their ultra-long spin relaxation time in the field of molecular spintronics. Since the first demonstration of truly worked vertical OSV device in 2004, efforts in enhancement of high performance and pursuit of spin-related nature have been devoted in related field. It offers a new opportunity to develop the integrated flexible multi-functional arrays based on spintronics in the future. However, the unreliable working state in OSVs due to the lack of exploration on interface control will cause severe impact on the performance evaluation and further restrict their practical application. Herein, we focus on the recent progress in strategies for reliable fabrication and evaluation of typical OSVs in vertical configuration. Firstly, the challenges in protection of two spin interface properties and identification of spin-valve-like signals were proposed. Then, three points for attention including selection of bottom electrodes, optimization of organic spacer, and prevention of metal penetration to improve the device performance and reliability were mentioned. Particularly, various modified strategies to solve the "dead layer" issue were highlighted. Furthermore, we discussed the general protocols in the reliable evaluation of OSVs' performance and transport mechanism identification. Notably, several key fundamentals resulting in spurious magnetoresistance (MR) response were illustrated. Finally, we also highlighted the future perspectives on spintronic devices of organic materials. [ABSTRACT FROM AUTHOR]

GaAs is well known for its extremely high electron mobility and direct band gap. Owing to the technological advances in silicon-based technology, GaAs has been limited to niche areas. This paper discusses the application of GaAs in molecular electronics and spintronics as a potential field for considering this amazing but challenging material. GaAs is challenging because its surface is characterized by a high density of surface states, which precludes the utilization of this semiconducting material in mainstream devices. Sulfur(S)-based passivation has been found to be significantly useful for reducing the effect of dangling bonds and was researched thoroughly. GaAs applications in molecular spintronics and electronics can benefit significantly from prior knowledge of GaAs and S interactions because S is a popular functional group for bonding molecular device elements with different semiconductors and metals. In this article, the problem associated with the GaAs surface is discussed in a tutorial form. A wide variety of surface passivation methods has been briefly introduced. We attempted to highlight the significant differences in the S-GaAs interactions for different S passivation methods. We also elaborate on the mechanisms and atomic-scale understanding of the variation in surface chemistry and reconstruction due to various S passivation methods. It is envisioned that GaAs and thiol-terminated molecule-based novel devices can exhibit innovative device characteristics and bring the added advantage of S-based passivation.

The investigation focused on examining the spin polarization and thermal spin polarization transport characteristics of dual rhenium phthalocyanine (Re2PC2) molecular junctions. This analysis was conducted using first-principles density-functional theory and the non-equilibrium Green's function approach. Calculations were performed on molecular junctions in two configurations: one at a non-magnetic electrode (Au) and the other at a magnetic electrode (Ni). A comparison of the spin transport properties of the two electrodes shows significant differences. The magnetic electrode has a notable effect on the spin-polarization and thermal spin-polarization transport properties of the devices. In contrast, the nickel electrode bis-phthalocyanine rhenium molecular device exhibits perfect spin/thermal spin-filtering efficiencies in a parallel structure. The properties of the dual phthalocyanine rhenium molecular devices were significantly affected by the nature of the electrodes. This makes dual rhenium phthalocyanine molecular junctions have great potential for the development of high-performance multifunctional spintronic and spin caloritronic devices. • The nickel electrode Re2PC2 molecular device showed perfect spin/thermal SFE at parallel structure. • PDOS revealed that the transport properties of Re2PC2 molecules were strongly influenced by the magnetic electrode. • Changing the direction of the magnetic moments of the molecules and electrodes can alter the device's characteristics. [ABSTRACT FROM AUTHOR]

A new type of spin-current filter is proposed that consists of a single-molecule magnet (SMM) coupled to two normal metal electrodes. It is shown that this tunneling junction can generate a highly spin-polarized current, whose spin polarization can be switched by means of magnetic fields and gate voltages applied to the SMM. This spin switching in the SMM tunnel junction arises from spin-selective single-electron resonant tunneling via the lowest unoccupied molecular orbit of the SMM. The electron current spectrum is still spin polarized in the absence of an external magnetic field, which can help to judge whether the molecule’s spin state has reached the ground-state doublet | ± S ⟩ . This device can be realized with current technologies and may have practical use in spintronics and quantum information. [ABSTRACT FROM AUTHOR]

Due to its unique magnetic properties offered by the open‐shell electronic structure of the central metal ion, and for being an effective catalyst in a wide variety of reactions, iron phthalocyanine has drawn significant interest from the scientific community. Nevertheless, upon surface deposition, the magnetic properties of the molecular layer can be significantly affected by the coupling occurring at the interface, and the more reactive the surface, the stronger is the impact on the spin state. Here, we show that on Cu(100), indeed, the strong hybridization between the Fe d‐states of FePc and the sp‐band of the copper substrate modifies the charge distribution in the molecule, significantly influencing the magnetic properties of the iron ion. The FeII ion is stabilized in the low singlet spin state (S=0), leading to the complete quenching of the molecule magnetic moment. By exploiting the FePc/Cu(100) interface, we demonstrate that NO2 dissociation can be used to gradually change the magnetic properties of the iron ion, by trimming the gas dosage. For lower doses, the FePc film is decoupled from the copper substrate, restoring the gas phase triplet spin state (S=1). A higher dose induces the transition from ferrous to ferric phthalocyanine, in its intermediate spin state, with enhanced magnetic moment due to the interaction with the atomic ligands. Remarkably, in this way, three different spin configurations have been observed within the same metalorganic/metal interface by exposing it to different doses of NO2 at room temperature. [ABSTRACT FROM AUTHOR]

Molecular semiconductor (MSC) is a promising candidate for spintronic applications benefiting from its long spin lifetime caused by light elemental-composition essence and thus weak spin-orbit coupling (SOC). According to current knowledge, the SOC effect, normally dominated by the elemental composition, is the main spin-relaxation causation in MSCs, and thus the molecular structure-induced SOC change is one of the most concerned issues. In theoretical study, molecular isomerism, a most prototype phenomenon, has long been considered to possess little difference on spin transport previously, since elemental compositions of isomers are totally the same. However, here in this study, quite different spin-transport performances are demonstrated in ITIC and its structural isomers BDTIC experimentally, for the first time, though the charge transport and molecular stacking of the two films are very similar. By further experiments of electron-paramagnetic resonance and density-functional-theory calculations, it is revealed that noncovalent-conformational locks (NCLs) formed in BDTIC can lead to enhancement of SOC and thus decrease the spin lifetime. Hence, this study suggests the influences from the structural-isomeric effect must be considered for developing highly efficient spin-transport MSCs, which also provides a reliable theoretical basis for solving the great challenge of quantificational measurement of NCLs in films in the future., (© 2024 Wiley‐VCH GmbH.)

The spin states of three earlier described cobalt(II) clathrochelates as films on the quartz supports are studied for the first time. The magnetochemical study shows that the temperature-induced spin transition observed previously in the crystalline samples is retained in the films, which makes it possible to consider this class of coordination compounds with high chemical and thermal stability as promising components for molecular spintronic devices. [ABSTRACT FROM AUTHOR]

Molecular magnetism has made a long journey, from the fundamental studies on through-ligand electron exchange magnetic interactions in dinuclear metal complexes with extended organic bridges to the more recent exploration of their electron spin transport and quantum coherence properties. Such a field has witnessed a renaissance of dinuclear metallacyclic systems as new experimental and theoretical models for single-molecule spintronics and quantum computing, due to the intercrossing between molecular magnetism and metallosupramolecular chemistry. The present review reports a state-of-the-art overview as well as future perspectives on the use of oxamato-based dicopper(II) metallacyclophanes as promising candidates to make multifunctional and multiresponsive, single-molecule magnetic (nano)devices for the physical implementation of quantum information processing (QIP). They incorporate molecular magnetic couplers, transformers, and wires, controlling and facilitating the spin communication, as well as molecular magnetic rectifiers, transistors, and switches, exhibiting a bistable (ON/OFF) spin behavior under external stimuli (chemical, electronic, or photonic). Special focus is placed on the extensive research work done by Professor Francesc Lloret, an outstanding chemist, excellent teacher, best friend, and colleague, in recognition of his invaluable contributions to molecular magnetism on the occasion of his 65th birthday. [ABSTRACT FROM AUTHOR]

Using an ab initio method based on non-equilibrium Green's functions (NEGF) combined with density functional theory (DFT), a calculation of the transport properties of a single molecular junction based on 1,3-diphenylpropynylidene (PhC3Ph) 'radical-π-radical' is performed. The obvious negative differential resistance (NDR), spin current polarisation (SCP) and dual-spin current rectification (SCR) effects in this device are obtained. The total current for magnetic parallel configuration (PC) is larger at first and then less than that for magnetic antiparallel configuration (APC) as the bias increases, which suggests the abnormal magnetoresistance (MR) effect and can be used as a molecular switch with two working voltages. The evolution of the spin-polarised transmission spectrums and the frontier molecular orbitals (MOs) with applied bias is used to explain the above interesting results. Our calculations may be helpful for designing multifunctional molecular spintronics devices in the future. [ABSTRACT FROM AUTHOR]

Pinching molecules via chemical strain suggests intuitive consequences, such as compression at the pinched site and clothespin‐like opening of other parts of the structure. If this opening affects two spin centers, it should result in reduced communication between them. We show that for naphthalene‐bridged biscobaltocenes with competing through‐space and through‐bond pathways, the consequences of pinching are far less intuitive: despite the known dominance of through‐space interactions, the bridge plays a much larger role for exchange spin coupling than previously assumed. Based on a combination of chemical synthesis, structural, magnetic, and redox characterization, and a newly developed theoretical pathway analysis, we can suggest a comprehensive explanation for this non‐intuitive behavior. These results are of interest for molecular spintronics, as naphthalene‐linked cobaltocenes can form wires on surfaces for potential spin‐only information transfer. [ABSTRACT FROM AUTHOR]

We report on a new approach for the fabrication of ferromagnetic molecular thin films. Co-evaporated films of manganese phthalocyanine (MnPc) and tetracyanoquinodimethane (TCNQ) have been produced by organic molecular beam deposition (OMBD) on rigid (glass, silicon) and flexible (Kapton) substrates kept at room temperature. The MnPc:TCNQ films are found to be entirely amorphous due to the size mismatch of the molecules. However, by annealing while covering the samples highly crystalline MnPc films in the β-polymorph can be obtained at 60 °C lower than when starting with pure MnPc films. The resulting films exhibit substantial coercivity (13 mT) at 2 K and a Curie temperature of 11.5 K.

Abstract The stability of magnetic information stored in surface adsorbed single‐molecule magnets is of critical interest for applications in nanoscale data storage or quantum computing. The present study combines X‐ray magnetic circular dichroism, density functional theory and magnetization dynamics calculations to gain deep insight into the substrate dependent relevant magnetization relaxation mechanisms. X‐ray magnetic circular dichroism reveals the opening of a butterfly‐shaped magnetic hysteresis of DyPc2 molecules on magnesium oxide and a closed loop on the bare silver substrate, while density functional theory shows that the molecules are only weakly adsorbed in both cases of magnesium oxide and silver. The enhanced magnetic stability of DyPc2 on the oxide film, in conjunction with previous experiments on the TbPc2 analogue, points to a general validity of the magnesium oxide induced stabilization effect. Magnetization dynamics calculations reveal that the enhanced magnetic stability of DyPc2 and TbPc2 on the oxide film is due to the suppression of two‐phonon Raman relaxation processes. The results suggest that substrates with low phonon density of states are beneficial for the design of spintronics devices based on single‐molecule magnets.

Because of the considerable advantages of functional molecules as well as supramolecules, such as the low cost, light weight, flexibility, and large area preparation via the solution method, molecular electronics has grown into an active and rapidly developing research field over the past few decades. Beyond those well-known advantages, a very long spin relaxation time of π-conjugated molecules, due to the weak spin-orbit coupling, facilitates a pioneering but fast-growing research field, known as molecular spintronics. Recently, a series of sustained progresses have been achieved with various π-conjugated molecular matrixes where spin transport is undoubtedly an important point for the spin physical process and multifunctional applications. Currently, most studies on spin transport are carried out with a molecule-based spin valve, which shows a typical geometry with a thin-film molecular layer sandwiched between two ferromagnetic electrodes. In such a device, the spin transport process has been demonstrated to have a close correlation with spin relaxation time and charge carrier mobility of π-conjugated molecules. In this review, the recent advances of spin transport in these two aspects have been systematically summarized. Particularly, spin transport in π-conjugated molecular materials, considered as promising for spintronics development, have also been highlighted, including molecular single crystal, cocrystal, solid solution as well as other highly ordered supramolecular structures.

The anchoring of the molecule to an electrode is known to be a key factor in single-molecule spintronics experiments. Likewise, a relaxation down to the most stable geometry is a critical step in theoretical simulations of transport through single-molecule junctions. Herein we present a set of calculations designed to analyze and compare the effect of different anchoring points and the effect of perturbations in the molecular geometry and interelectrode distance. As model system we chose the [V(α-C 3 S 5) 3 ]2− complex connecting two Au(1 1 1) electrodes in a slightly compressed geometry. In our calculations, the attachment happens through an S-Au bond, a common anchoring strategy in molecular spintronics experiments. Our results confirm that small alterations in the molecular geometry have important effects in the conductance. We were able to compare these effects with the ones arising from changing the anchoring position with a constant molecular geometry. Unexpectedly, we demonstrate that the anchoring position has only a lesser relevance in the spintronic behavior of the device, as long as all other parameters are kept frozen. As a consequence, we predict that for experimentalists aiming for reproducibility, the molecular design of rigid linkers is more relevant than the design of univocal anchoring positions. [ABSTRACT FROM AUTHOR]

The adsorbed magnetic molecules with tunable spin states have drawn wide attention for their immense potential in the emerging fields of molecular spintronics and quantum computing. One of the key issues toward their application is the efficient controlling of their spin state. This review briefly summarizes the recent progress in the field of molecular spin state manipulation on surfaces. We focus on the molecular spins originated from the unpaired electrons of which the Kondo effect and spin excitation can be detected by scanning tunneling microscopy and spectroscopy (STM and STS). Studies of the molecular spin-carriers in three categories are overviewed, i.e., the ones solely composed of main group elements, the ones comprising 3d-metals, and the ones comprising 4f-metals. Several frequently used strategies for tuning molecular spin state are exemplified, including chemical reactions, reversible atomic/molecular chemisorption, and STM-tip manipulations. The summary of the successful case studies of molecular spin state manipulation may not only facilitate the fundamental understanding of molecular magnetism and spintronics but also inspire the design of the molecule-based spintronic devices and materials.

Graphene-based electrodes are very promising for molecular electronics and spintronics. Here we report a systematic characterization of the electroburning (EB) process, leading to the formation of nanometer-spaced gaps, on different types of few-layer graphene (namely mechanically exfoliated graphene on SiO2, graphene epitaxially grown on the C-face of SiC and turbostratic graphene discs deposited on SiO2) under air and vacuum conditions. The EB process is found to depend on both the graphene type and on the ambient conditions. For the mechanically exfoliated graphene, performing EB under vacuum leads to a higher yield of nanometer-gap formation than working in air. Conversely, for graphene on SiC the EB process is not successful under vacuum. Finally, the EB is possible with turbostratic graphene discs only after the creation of a constriction in the sample using lithographic patterning.

Abstract Molecular bridges covalently bonded to two ferromagnetic electrodes can transform ferromagnetic materials and produce intriguing spin transport characteristics. Previously, we theoretically and experimentally studied the impact of paramagnetic molecules on the magnetic properties of the magnetic tunnel junctions (Tyagi et al. Nanotechnology, Vol.26, p.305602, 2015). In this follow up paper we have investigated the impact of previously demonstrated molecule induced strong coupling on the spin transport. To study molecular coupling effect experimentally we attached paramagnetic molecules between two ferromagnetic electrodes of a magnetic tunnel junction along the exposed side edges. The strong molecule coupling between two ferromagnetic electrodes caused the drastic changes in transport properties of the magnetic tunnel junction testbed. Molecular transport channels along the tunnel junction edges decreased the tunneling current as compared to the leakage current of the bare tunnel junction at room temperature. The current magnitude on the paramagnetic molecule treated magnetic tunnel junction tended to settle in the suppressed state at room temperature. Graphical abstract Image 1 Highlights • Covalently bonded molecules created experimentally-observed strong antiferromagnetic coupling between ferromagnets of MTJ. • Upto ~ 7 orders of current reduction below leakage current of MTJ occurred on MTJMSD due to molecular bridges at RT. • In the transient state MTJ+molecules (aka MTJMSD) showed irreproducible magnetoresistance change by >1000 folds at RT. • In the transient state forcing current through MTJMSD showed irreproducible resistance change by >1000 folds at RT. • MTJMSD approach may allow mass production of molecular quantum properties based future computing and memory devices. [ABSTRACT FROM AUTHOR]

We have investigated spin relaxation and spin-to-charge conversion at the Cu surface decorated with lead (II) phthalocyanine (PbPc) molecules. The study on the frequency dependence of ferromagnetic resonance linewidth revealed that the Cu/PbPc interface exhibits more pronounced spin relaxation than that of the Cu/H2Pc (metal-free phthalocyanine) interface. A clear peak owing to the spin-to-charge conversion was observed in the spin-pumping-induced voltage spectrum for a NiFe/Cu/PbPc trilayer film, whereas no trace of peak was observed in the film with NiFe/Cu/H2Pc. These results might be attributed to the Rashba effect at Cu surface by the decoration with PbPc, which indicates the new possibility of molecular spintronics. [ABSTRACT FROM AUTHOR]

Abstract: Cross-fertilization between molecular magnetism and organic spintronics is leading to the development of concepts based on the use of molecules as active elements to influence spin-related transport processes. The research on hybrid devices, where the magnetic molecules in contact with the electrodes influence the spin and charge injection and transport, is moving its first steps but is expected to quickly expand the technological potential of molecular spintronics and quantum computing. New exciting possibilities, linked to the individual properties of these molecular units and to their interaction with novel substrates, are getting disclosed. The chemical functionalization of these molecules is the tool which allows to tune their electronic and magnetic properties and to directly create these hybrid architectures. However, the coupling of molecules with the spin transport phenomena is far from being trivial. First, the stability of molecules in the device environment must be tested and, subsequently, the organization of molecules in the desired architectures must be mastered permitting a careful control of the interactions between inorganic substrates and molecular layers. Here we summarize how this research activity can be developed in the case of one of the simplest magnetic molecules, an organic radical. We will start from an innocent surface, such as gold, to move then toward a real-device environment. We evidence how these efforts can result in a surface-specific molecular-based method to influence the spin injection and transport phenomena, paving the way for developing new devices in which a fine-tuning of magnetic features is required.Graphical abstract: [ABSTRACT FROM AUTHOR]

By applying a first-principles approach based on non-equilibrium Green's functions combined with density functional theory, the transport properties of a pyridinium-based “radical- π -radical” molecular spintronics device are investigated. The obvious negative differential resistance (NDR) and spin current polarization (SCP) effect, and abnormal magnetoresistance (MR) are obtained. Orbital reconstruction is responsible for novel transport properties such as that the MR increases with bias and then decreases and that the NDR being present for both parallel and antiparallel magnetization configurations, which may have future applications in the field of molecular spintronics. [ABSTRACT FROM AUTHOR]

Molecular bridges covalently bonded to two ferromagnetic electrodes can transform ferromagnetic materials and produce intriguing spin transport characteristics. This paper discusses the impact of molecule induced strong coupling on the spin transport. To study molecular coupling effect the octametallic molecular cluster (OMC) was bridged between two ferromagnetic electrodes of a magnetic tunnel junction (Ta/Co/NiFe/AlOx/NiFe/Ta) along the exposed side edges. OMCs induced strong inter-ferromagnetic electrode coupling to yield drastic changes in transport properties of the magnetic tunnel junction testbed at the room temperature. These OMCs also transformed the magnetic properties of magnetic tunnel junctions. SQUID and ferromagnetic resonance studies provided insightful data to explain transport studies on the magnetic tunnel junction based molecular spintronics devices. [ABSTRACT FROM AUTHOR]

Abstract: A multifunctional spin quantum device obtained by sandwiching 11‐mercaptoundeca‐2,4,8,10‐tetraenenitrile, a donor–σ–acceptor molecule, between gold and iron electrodes is proposed. The device can act as a spin rectifier at lower bias and also exhibits negative differential resistance (NDR) after attaining a bias of 1.3 V. The rectification feature is quite prominent in the spin‐up channel, with an appreciable rectification ratio of 68, whereas the NDR indicator, that is, the peak to valley ratio (≈10) of the current–voltage characteristics after 1.3 V, is also quite significant. To understand the origin of this in silico observation, nonequilibrium green's function based DFT calculations have been performed. Analyses reveal that both properties originate from the bias‐independent energy offset between the frontier orbitals and electrode Fermi levels, popularly known as Fermi‐level pinning. More precisely, rectification results from the Fermi‐level pinning of the HOMO and LUMO with the gold and iron electrodes, respectively; the Fermi‐level pinning forces a HOMO–LUMO crossover that helps to explain the origin of the NDR. [ABSTRACT FROM AUTHOR]

We present a theoretical study on the adsorption and spin transport properties of magnetic Fe@C28 using Ab initio calculations based on spin density functional theory and non-equilibrium Green’s function techniques. Fe@C28 tends to adsorb on the bridge sites in the manner of C−C bonds, and the spin-resolved transmission spectra of Fe@C28 molecular junctions exhibit robust transport spin polarization (TSP). Under small bias voltage, the transport properties of Fe@C28 are mainly determined by the spin-down channel and exhibit a large spin polarization. When compressing the right electrode, the TSP is decreased, but high spin filter efficiency (SFE) is still maintained. These theoretical results indicate that Fe@C28 with a large magnetic moment has potential applications in molecular spintronics.