Direct observation of a highly spin-polarized organic spinterface at room temperature

The Role of Rare-Earth Atoms in the Anisotropy and Antiferromagnetic Exchange Coupling at a Hybrid Metal-Organic Interface

Magnetic anisotropy and magnetic exchange interactions are crucial parameters that characterize the hybrid metal-organic interface, a key component of an organic spintronic device. It is shown that the incorporation of 4f RE atoms to hybrid metal-organic interfaces of CuPc/REAu2 type (RE = Gd, Ho) constitutes a feasible approach toward on-demand magnetic properties and functionalities. The GdAu2 and HoAu2 substrates differ in their magnetic anisotropy behavior. Remarkably, the HoAu2 surface promotes the inherent out-of-plane anisotropy of CuPc, owing to the match between the anisotropy axis of substrate and molecule. Furthermore, the presence of RE atoms leads to a spontaneous antiferromagnetic exchange coupling at the interface, induced by the 3d-4f superexchange interaction between the unpaired 3d electron of CuPc and the 4f electrons of the RE atoms. It is shown that 4f RE atoms with unquenched quantum orbital momentum ( L $L$ ), as it is the case of Ho, induce an anisotropic interfacial exchange coupling.

Room-temperature-persistent magnetic interaction between coordination complexes and nanoparticles in maghemite-based nanohybrids

Maghemite nanoparticles functionalised with Co(II) coordination complexes at their surface show a significant increase of their magnetic anisotropy, leading to a doubling of the blocking temperature and a sixfold increase of the coercive field. Magnetometric studies suggest an enhancement that is not related to surface disordering, and point to a molecular effect involving magnetic exchange interactions mediated by the oxygen atoms at the interface as its source. Field- and temperature-dependent X-ray absorption spectroscopy (XAS) and X-ray magnetic circular dichroism (XMCD) studies show that the magnetic anisotropy enhancement is not limited to surface atoms and involves the core of the nanoparticle. These studies also point to a mechanism driven by anisotropic exchange and confirm the strength of the magnetic exchange interactions. The coupling between the complex and the nanoparticle persists at room temperature. Simulations based on the XMCD data give an effective exchange field value through the oxido coordination bridge between the Co(II) complex and the nanoparticle that is comparable to the exchange field between iron ions in bulk maghemite. Further evidence of the effectiveness of the oxido coordination bridge in mediating the magnetic interaction at the interface is given with the Ni(II) analog to the Co(II) surface-functionalised nanoparticles. A substrate-induced magnetic response is observed for the Ni(II) complexes, up to room temperature.

Molecular Compounds in Spintronic Devices: An Intricate Marriage of Chemistry and Physics

Spintronics, a flourishing new field of microelectronics, uses the electron spin for reading and writing information in modern computers and other spintronic devices with a low power consumption and high reliability. In a quest to increase the productivity of such devices, the use of molecular materials as a spacer layer allowed them to perform equally well or even better than conventional all-inorganic heterostructures from metals, alloys, or inorganic semiconductors. In this review, we survey various classes of chemical compounds that have already been tested for this purpose─from organic compounds and coordination complexes to organic-inorganic hybrid materials─since the creation of the first molecule-based spintronic device in 2002. Although each class has its advantages, drawbacks, and applications in molecular spintronics, together they allowed nonchemists to gain insights into spin-related effects and to propose new concepts in the design and fabrication of highly efficient spintronic devices. Other molecular compounds that chemistry could offer in great numbers may soon emerge as suitable spacers or even electrodes in flexible magnetic field sensors, nonvolatile memories, and multifunctional spintronic devices.

Iron(II) Clathrochelates in Molecular Spintronic Devices: A Vertical Spin Valve

Abstract

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.

Room-Temperature Spin-Dependent Transport in Metalloporphyrin-Based Supramolecular Wires

Here we present room-temperature spin-dependent charge transport measurements in single-molecule junctions made of metalloporphyrin-based supramolecular assemblies. They display large conductance switching for magnetoresistance in a single-molecule junction. The magnetoresistance depends acutely on the probed electron pathway through the supramolecular wire: those involving the metal center showed marked magnetoresistance effects as opposed to those exclusively involving the porphyrin ring which present nearly complete absence of spin-dependent charge transport. The molecular junction magnetoresistance is highly anisotropic, being observable when the magnetization of the ferromagnetic junction electrode is oriented along the main molecular junction axis, and almost suppressed when it is perpendicular. The key ingredients for the above effect to manifest are the electronic structure of the paramagnetic metalloporphyrin, and the spinterface created at the molecule-electrode contact.

Mo/Si lamellar multilayer gratings with high efficiency and enhanced resolution for the x-ray region of 1000-1700eV

The d-spacing of the multilayer lamellar grating was theoretically optimized to improve the energy resolution and maintain a high efficiency. Based on the study of the growth behavior of Mo/Si multilayer on the lamellar grating under different sputtering pressures, Ar gas pressure of 1 mTorr was selected, which can fabricate the multilayer with lower roughness and a good replication of the groove shape. An absolute diffraction efficiency of 25.6% and a Cff factor of 1.79 were achieved for the -1st order of the Mo/Si lamellar multilayer grating at an energy of 1700 eV.

Magnetism at the interface of non-magnetic Cu and C60

The signature of magnetism without a ferromagnet in a non-magnetic heterostructure is novel as well as fascinating from a fundamental research point of view. It has been shown by Al'Mari et al. that magnetism can be induced at the interface of Cu/C₆₀ due to a change in the density of states. However, the quantification of such an interfacial magnetic moment has not been performed yet. In order to quantify the induced magnetic moment in Cu, we have performed X-ray magnetic circular dichroism (XMCD) measurements on Cu/C₆₀ multilayers. We have observed room temperature ferromagnetism in the Cu/C₆₀ stack. Further XMCD measurements show that a ∼0.01 μ_B per atom magnetic moment has been induced in Cu at the Cu/C₆₀ interface.

Searching high spin polarization ferromagnet in Heusler alloy via machine learning

In order to search for stable ferromagnets with high spin polarization in Heusler alloys for spintronic applications, we develop an efficient machine learning workflow based on a deep neural network, whose training data were collected from the open quantum materials database and high throughput calculation by first-principle calculations. The lattice constants, formation energy and spin polarization of 10 577 candidate materials were predicted, and 192 materials with high spin polarization were selected according to a spin polarization greater than 0.87 and formation energy less than 80 meV/atom. 57 of these alloys have been reported as Half-metal (100% spin polarization) according to previous researches, and 18 have been reported as semiconductors. Especially, 6 Heusler alloys were identified as promising half-metallic ferromagnets, and some of them have high Curie temperature above room temperature. Our study suggests this approach is an efficient method for the discovery of superior spintronic materials, which should be also suitable for exploring other functional materials.

Interface hybridization and spin filter effect in metal-free phthalocyanine spin valves

Spin–orbit coupling has been regarded as the core interaction to determine the efficiency of spin conserved transport in semiconductor spintronics. Here, we show the spin filter effect should be responsible for the magnetoresistance of H₂Pc device.

Iron Phthalocyanine and Ferromagnetic Thin Films: Magnetic Behavior of Single and Double Interfaces

Metal-phthalocyanines are quasi-planar heterocyclic macrocycle molecules with a highly conjugated structure. They can be engineered at the molecular scale (central atom, ligand) to tailor new properties for organic spintronics devices. In this study, we evaluated the magnetic behavior of FePc in a ∼1 nm molecular film sandwiched between two ferromagnetic films: cobalt (bottom) and nickel (top). In the single interface, FePc in contact with a Co film is magnetically coupled with the inorganic film magnetization, though the relatively small Fe(Pc) X-ray magnetic circular dichroism (XMCD) signal in remanence, with respect to that observed in applied field of 6 T, suggests that a fraction of molecules in the organometallic film have their magnetic moment not aligned or antiparallel with respect to Co. When in contact with two interfaces, Fe(Pc) XMCD doubles, indicating that part of the Fe(Pc) are now aligned with the Ni topmost layer, saturated at 1 T. We discussed the relevance of the finding in terms of understanding and developing hybrid organic/inorganic spin devices.

Molecular Tunability of Magnetic Exchange Bias and Asymmetrical Magnetotransport in Metalloporphyrin/Co Hybrid Bilayers

Individual molecular spins are promising quantum states for emerging computation technologies. The "on surface" configuration of molecules in proximity to a magnetic film allows control over the orientations of molecular spins and coupling between them. The stacking of planar molecular spins could favor antiferromagnetic interlayer couplings and lead to pinning of the magnetic underlayer via the exchange bias, which is extensively utilized in ultrafast and high-density spintronics. However, fundamental understanding of the molecular exchange bias and its operating features on a device has not been unveiled. Here, we showed tunable molecular exchange bias and its asymmetrical magnetotransport characteristics on a device by using the metalloporphyrin/cobalt hybrid films. A series of the distinctive molecular layers showcased a wide range of the interfacial exchange coupling and bias. The transport behaviors of the hybrid bilayer films revealed the molecular exchange bias effect on a fabricated device, representing asymmetric characteristics on anisotropic and angle-dependent magnetoresistances. Theoretical simulations demonstrated close correlations among the interfacial distance, magnetic interaction, and exchange bias. This study of the hybrid interfacial coupling and its impact on magnetic and magnetotransport behaviors will extend functionalities of molecular spinterfaces for emerging information technologies.

Electronic and magnetic properties of a ferromagnetic cobalt surface by adsorbing ultrathin films of tetracyanoethylene

Ultrathin films of tetracyanoethylene (TCNE) on Co(100) were investigated by means of spin-integrated and spin-resolved photoemission spectroscopy ((sp-)UPS), X-ray photoemission spectroscopy (XPS), near edge X-ray absorption fine-structure spectroscopy (NEXAFS), and X-ray magnetic circular dichroism (XMCD). We found a coverage-dependent modulation of the interface dipole and a switching between a metallic and a resistive spin filtering at the interface triggered by two distinct adsorption geometries of TCNE. The strongest hybridization and spin structure modifications are found at low coverage with a face-on adsorption geometry indicating changes in the distance between the surface Co atoms beneath. TCNE has the potential to manipulate the magnetic moments in the Co surface itself, including the possibility of magnetic hardening effects. In summary, the system TCNE/Co offers an experimentally rather easy and controllable way to build up a stable molecular platform stabilizing the reactive ferromagnetic Co surface and customizing the electronic and magnetic properties of the resulting spinterface simultaneously. This makes this system very attractive for spintronic applications as an alternative, less reactive but highly spin polarized foundation beside graphene-based systems.

Interfacial Spin Manipulation of Nickel-Quinonoid Complex Adsorbed on Co(001) Substrate

We studied the structural, electronic, and magnetic properties of a recently synthesized Ni(II)-quinonoid complex upon adsorption on a magnetic Co(001) substrate. Our density functional theory + U (DFT+U) calculations predict that the molecule undergoes a spin-state switching from low-spin S = 0 in the gas phase to high-spin S ≈ 1 when adsorbed on the Co(001) surface. A strong covalent interaction of the quinonoid rings and surface atoms leads to an increase of the Ni–O(N) bond lengths in the chemisorbed molecule that support the spin-state switching. Our DFT+U calculations show that the molecule is ferromagnetically coupled to the substrate. The Co surface–Ni center exchange mechanism was carefully investigated. We identified an indirect exchange interaction via the quinonoid ligands that stabilizes the molecule’s spin moment in ferromagnetic alignment with the Co surface magnetization.

Quenching of Spin Polarization Switching in Organic Multiferroic Tunnel Junctions by Ferroelectric "Ailing-Channel" in Organic Barrier

The ferroelectric control of spin-polarization at ferromagnet (FM)/ferroelectric organic (FE-Org) interface by electrically switching the ferroelectric polarization of the FE-Org has been recently realized in the organic multiferroic tunnel junctions (OMFTJs) and gained intensive interests for future multifunctional organic spintronic applications. Here, we report the evidence of ferroelectric "ailing-channel" in the organic barrier, which can effectively pin the ferroelectric domain, resulting in nonswitchable spin polarization at the FM/FE-Org interface. In particular, OMFTJs based on La_0.6Sr_0.4MnO₃/P(VDF-TrFE) ( t)/Co/Au structures with different P(VDF-TrFE) thickness ( t) were fabricated. The combined advanced electron microscopy and spectroscopy studies clearly reveal that very limited Co diffusion exists in the P(VDF-TrFE) organic barrier when the Au/Co electrode is deposited around 80K. Pot-hole structures at the boundary between the P(VDF-TrFE) needle-like grains are evidenced to induce "ailing-channels" that hinder efficient ferroelectric polarization of the organic barrier and result in the quenching of the spin polarization switching at Co/P(VDF-TrFE) interface. Furthermore, the spin diffusion length in the negatively polarized P(VDF-TrFE) is measured to be about 7.2 nm at 20K. The evidence of the mechanism of ferroelectric "ailing-channels" is of essential importance to improve the performance of OMFTJ and master the key condition for an efficient ferroelectric control of the spin polarization of "spinterface".

Magnetoresistance Effect and the Applications for Organic Spin Valves Using Molecular Spacers

Organic spin devices utilizing the properties of both spin and charge inherent in electrons have attracted extensive research interest in the field of future electronic device development. In the last decade, magnetoresistance effects, including giant magetoresistance and tunneling magnetoresistance, have been observed in organic spintronics. Significant progress has been made in understanding spin-dependent transport phenomena, such as spin injection or tunneling, manipulation, and detection in organic spintronics. However, to date, materials that are effective for preparing organic spin devices for commercial applications are still lacking. In this report, we introduce basic knowledge of the fabrication and evaluation of organic spin devices, and review some remarkable applications for organic spin valves using molecular spacers. The current bottlenecks that hinder further enhancement for the performance of organic spin devices is also discussed. This report presents some research ideas for designing organic spin devices operated at room temperature.

Light-Induced Spin Crossover in an Fe(II) Low-Spin Complex Enabled by Surface Adsorption

Understanding and controlling the spin-crossover properties of molecular complexes can be of particular interest for potential applications in molecular spintronics. Using near-edge X-ray absorption fine structure spectroscopy, we investigated these properties for a new vacuum-evaporable Fe(II) complex, namely [Fe(pypyr(CF₃)₂)₂(phen)] (pypyr = 2-(2'-pyridyl)pyrrolide, phen = 1,10-phenanthroline). We find that the spin-transition temperature, well above room temperature for the bulk compound, is drastically lowered for molecules arranged in thin films. Furthermore, while within the experimentally accessible temperature range (2 K < T < 410 K) the bulk material shows indication of neither light-induced excited spin-state trapping nor soft X-ray-induced excited spin-state trapping, these effects are observed for molecules within thin films up to temperatures around 100 K. Thus, by arranging the molecules into thin films, a nominal low-spin complex is effectively transformed into a spin-crossover complex.

Robust and Selective Switching of an FeIII Spin-Crossover Compound on Cu2N/Cu(100) with Memristance Behavior

The switching between two spin states makes spin-crossover molecules on surfaces very attractive for potential applications in molecular spintronics. Using scanning tunneling microscopy, the successful deposition of [Fe(pap)₂]⁺ (pap = N-2-pyridylmethylidene-2-hydroxyphenylaminato) molecules on Cu₂N/Cu(100) surface is evidenced. The deposited Fe^III spin-crossover compound is controllably switched between three different states, each of them exhibiting a characteristic tunneling conductance. The conductance is therefore employed to readily read the state of the molecules. A comparison of the experimental data with the results of density functional theory calculations reveals that all Fe(pap)₂ molecules are initially in their high-spin state. The two other states are compatible with the low-spin state of the molecule but differ with respect to their coupling to the substrate. As a proof of concept, the reversible and selective nature of the switching is used to build a two-molecule memory.

Charge transfer from and to manganese phthalocyanine: bulk materials and interfaces

Manganese phthalocyanine (MnPc) is a member of the family of transition-metal phthalocyanines, which combines interesting electronic behavior in the fields of organic and molecular electronics with local magnetic moments. MnPc is characterized by hybrid states between the Mn 3d orbitals and the π orbitals of the ligand very close to the Fermi level. This causes particular physical properties, different from those of the other phthalocyanines, such as a rather small ionization potential, a small band gap and a large electron affinity. These can be exploited to prepare particular compounds and interfaces with appropriate partners, which are characterized by a charge transfer from or to MnPc. We summarize recent spectroscopic and theoretical results that have been achieved in this regard.

Inverse Magnetoresistance in Polymer Spin Valves

In this work, both negative and positive magnetoresistance (MR) in solution-processed regioregular poly(3-hexylthiophene) (RR-P3HT) is observed in organic spin valves (OSVs) with vertical La_2/3Sr_1/3MnO₃ (LSMO)/P3HT/AlO_x/Co configuration. The ferromagnetic (FM) LSMO electrode with near-atomic flatness is fabricated by a DC facing-target magnetron sputtering method. This research is focused on the origin of the MR inversion. Two types of devices are investigated in details: One with Co penetration shows a negative MR of 0.2%, while the other well-defined device with a nonlinear behavior has a positive MR of 15.6%. The MR measurements in LSMO/AlO_x/Co and LSMO/Co junctions are carried to exclude the interference of insulating layer and two FM electrodes themselves. By examining the Co thicknesses and their corresponding magnetic hysteresis loops, a spin-dependent hybrid-interface-state model by Co penetration is induced to explain the MR sign inversion. These results proven by density functional theory (DFT) calculations may shed light on the controllable interfacial properties in designing novel OSV devices.

Activating the molecular spinterface

The miniaturization trend in the semiconductor industry has led to the understanding that interfacial properties are crucial for device behaviour. Spintronics has not been alien to this trend, and phenomena such as preferential spin tunnelling, the spin-to-charge conversion due to the Rashba-Edelstein effect and the spin-momentum locking at the surface of topological insulators have arisen mainly from emergent interfacial properties, rather than the bulk of the constituent materials. In this Perspective we explore inorganic/molecular interfaces by looking closely at both sides of the interface. We describe recent developments and discuss the interface as an ideal platform for creating new spin effects. Finally, we outline possible technologies that can be generated thanks to the unique active tunability of molecular spinterfaces.

Deposition of a Cationic FeIII Spin-Crossover Complex on Au(111): Impact of the Counter Ion

Spin-crossover molecules on metallic substrates have recently attracted considerable interest for their potential applications in molecular spintronics. Using scanning tunneling microscopy, we evidence the first successful deposition of a charged Fe^III spin-crossover complex, [Fe(pap)₂]⁺ (pap = N-2-pyridylmethylidene-2-hydroxyphenylaminato), on Au(111). Furthermore, the bulk form of the molecules is stabilized by a perchlorate counterion, which depending on the deposition technique may affect the quality of the deposition and the measurements. Finally, we evidence switching of the molecules on Au(111).

Ferroelectric Control of Organic/Ferromagnetic Spinterface

Organic multiferroic tunnel junctions based on La_0.6 Sr_0.4 MnO₃ /poly(vinylidene fluoride) (PVDF)/Co structures are fabricated. The tunneling magneto-resistance sign can be changed by electrically switching the ferroelectric polarization of PVDF barrier. It is demonstrated that the spin-polarization of the PVDF/Co spinterface can be actively controlled by tuning the ferroelectric polarization of PVDF. This study opens new functionality in controlling the injection of spin polarization into organic materials via the ferroelectric polarization of the barrier.

High Spin Polarization at Ferromagnetic Metal-Organic Interfaces: A Generic Property

A high spin polarization of states around the Fermi level, EF, at room temperature has been measured in the past at the interface between a few molecular candidates and the ferromagnetic metal Co. Is this promising property for spintronics limited to these candidates? Previous reports suggested that certain conditions, such as strong ferromagnetism, i.e., a fully occupied spin-up d band of the ferromagnet, or the presence of π bonds on the molecule, i.e., molecular conjugation, needed to be met. What rules govern the presence of this property? We have performed spin-resolved photoemission spectroscopy measurements on a variety of such interfaces. We find that this property is robust against changes to the molecule and ferromagnetic metal's electronic properties, including the aforementioned conditions. This affirms the generality of highly spin-polarized states at the interface between a ferromagnetic metal and a molecule and augurs bright prospects toward integrating these interfaces within organic spintronic devices.

Electronic and magnetic properties of TTF and TCNQ covered Co thin films

Interfacial effects like orbital hybridization and charge transfer strongly influence the transfer of spins from ferromagnetic metals to organic semiconductors and can lead to the formation of interfacial states with distinct magnetic properties. The changes in the electronic and magnetic properties of a thin Co film upon adsorption of a layer of either the molecular organic electron donor tetrathiafulvalene (TTF) or the acceptor tetracyanoquinodimethane (TCNQ) have been investigated by X-ray absorption spectroscopy and X-ray magnetic circular dichroism using synchrotron radiation. Clear differences between the spectra of the adsorbed molecules and the neutral molecules show the hybridization of the molecular orbitals with the Co interface. Deposition of both organic materials leads to a small increase of the ratio of the orbital magnetic moment to the spin magnetic moment of the Co atoms at the interface. The main effect of overlayer deposition is a modification of the magnetic hysteresis of the Co film: The TCNQ slightly reduces the coercivity of the Co, while the TTF increases the coercivity by a factor of ∼1.5. These complementary effects of either a molecular organic electron donor or acceptor on the interfacial properties of a metal ferromagnetic thin film are a promising result for the controlled modification of the magnetic structure of hybrid interfaces.

Versatile variable temperature insert at the DEIMOS beamline for in situ electrical transport measurements

The design and the first experiments are described of a versatile cryogenic insert used for its electrical transport capabilities. The insert is designed for the cryomagnet installed on the DEIMOS beamline at the SOLEIL synchrotron dedicated to magnetic characterizations through X-ray absorption spectroscopy (XAS) measurements. This development was spurred by the multifunctional properties of novel materials such as multiferroics, in which, for example, the magnetic and electrical orders are intertwined and may be probed using XAS. The insert thus enables XAS to in situ probe this interplay. The implementation of redundant wiring and careful shielding also enables studies on operating electronic devices. Measurements on magnetic tunnel junctions illustrate the potential of the equipment toward XAS studies of in operando electronic devices.

Unconventional magnetisation texture in graphene/cobalt hybrids

Magnetic domain structure and spin-dependent reflectivity measurements on cobalt thin films intercalated at the graphene/Ir(111) interface are investigated using spin-polarised low-energy electron microscopy. We find that graphene-covered cobalt films have surprising magnetic properties. Vectorial imaging of magnetic domains reveals an unusually gradual thickness-dependent spin reorientation transition, in which magnetisation rotates from out-of-the-film plane to the in-plane direction by less than 10° per cobalt monolayer. During this transition, cobalt films have a meandering spin texture, characterised by a complex, three-dimensional, wavy magnetisation pattern. In addition, spectroscopy measurements suggest that the electronic band structure of the unoccupied states is essentially spin-independent already a few electron-Volts above the vacuum level. These properties strikingly differ from those of pristine cobalt films and could open new prospects in surface magnetism.

Exchange Coupling of Spin-Crossover Molecules to Ferromagnetic Co Islands

The properties of Fe(1,10-phenanthroline)2(NCS)2 (Fe-phen) molecules deposited on Co/Cu(111) are studied with scanning tunneling microscopy (STM) operated in ultrahigh vacuum at low temperature (4 K) and ab initio calculations. Both the experimental and theoretical results are used to identify the high-spin (HS) state of Fe-phen. Additionally, the calculations reveal a strong spin-polarization of the density of states (DOS) and is validated experimentally using the spin sensitivity of spin-polarized STM. Finally, it is shown that the magnetic moment of the Fe-ion within HS Fe-phen is strongly magnetically coupled to the underlying magnetic Co through the NCS groups. These findings enable promising spintronic perspectives.

Curvature-enhanced Spin-orbit Coupling and Spinterface Effect in Fullerene-based Spin Valves

We investigated curvature-enhanced spin-orbit coupling (SOC) and spinterface effect in carbon-based organic spin valves (OSVs) using buckyball C60 and C70 molecules. Since the naturally abundant (12)C has spinless nuclear, the materials have negligible hyperfine interaction (HFI) and the same intrinsic SOC, but different curvature SOC due to their distinct curvatures. We fitted the thickness dependence of magnetoresistance (MR) in OSVs at various temperatures using the modified Jullière equation. We found that the spin diffusion length in the C70 film is above 120 nm, clearly longer than that in C60 film at all temperatures. The effective SOC ratio of the C70 film to the C60 film was estimated to be about 0.8. This was confirmed by the magneto-electroluminescence (MEL) measurement in fullerene-based light emitting diodes (LED). Next, the effective spin polarization in C70-based OSVs is smaller than that in C60-based OSVs implying that they have different spinterface effect. First principle calculation study shows that the spin polarization of the dz(2) orbital electrons of Co atoms contacted with C60 is larger causing better effective spin polarization at the interface.

Phthalocyanine based molecular spintronic devices

Spin-dependent hybridization and spin excitation induce multiple magnetoresistance effects in phthalocyanine based spintronic devices.

Controlled manipulation of the Co–Alq3 interface by rational design of Alq3 derivatives

Recently, research has revealed that molecules can be used to steer the local spin properties of ferromagnetic surfaces.

Spin-Dependent Hybridization between Molecule and Metal at Room Temperature through Interlayer Exchange Coupling

We experimentally and theoretically show that the magnetic coupling at room temperature between paramagnetic Mn within manganese phthalocyanine molecules and a Co layer persists when separated by a Cu spacer. The molecule's magnetization amplitude and direction can be tuned by varying the Cu-spacer thickness and evolves according to an interlayer exchange coupling mechanism. Ab initio calculations predict a highly spin-polarized density of states at the Fermi level of this metal-molecule interface, thereby strengthening prospective spintronics applications.

Interfacial Properties of Organic Semiconductor-Inorganic Magnetic Oxide Hybrid Spintronic Systems Fabricated Using Pulsed Laser Deposition

We report fabrication of a hybrid organic semiconductor-inorganic complex oxide interface of rubrene and La0.67Sr0.33MnO3 (LSMO) for spintronic devices using pulsed laser deposition (PLD) and investigate the interface structure and chemical bonding-dependent magnetic properties. Our results demonstrate that with proper control of growth parameters, thin films of organic semiconductor rubrene can be deposited without any damage to the molecular structure. Rubrene, a widely used organic semiconductor with high charge-carrier mobility and spin diffusion length, when grown as thin films on amorphous and crystalline substrates such as SiO2-glass, indium-tin oxide (ITO), and LSMO by PLD at room temperature and a laser fluence of 0.19 J/cm2, reveals amorphous structure. The Raman spectra verify the signatures of both Ag and Bg Raman active modes of rubrene molecules. X-ray reflectivity measurements indicate a well-defined interface formation between surface-treated LSMO and rubrene, whereas X-ray photoelectron spectra indicate the signature of hybridization of the electronic states at this interface. Magnetic measurements show that the ferromagnetic property of the rubrene-LSMO interface improves by >230% compared to the pristine LSMO surface due to this proposed hybridization. Intentional disruption of the direct contact between LSMO and rubrene by insertion of a dielectric AlOx layer results in an observably decreased ferromagnetism. These experimental results demonstrate that by controlling the interface formation between organic semiconductor and half-metallic oxide thin films, it is possible to engineer the interface spin polarization properties. Results also confirm that by using PLD for consecutive growth of different layers, contamination-free interfaces can be obtained, and this finding is significant for the well-controlled and reproducible design of spin-polarized interfaces for future hybrid spintronics devices.

Exchange bias and room-temperature magnetic order in molecular layers

Molecular semiconductors may exhibit antiferromagnetic correlations well below room temperature. Although inorganic antiferromagnetic layers may exchange bias single-molecule magnets, the reciprocal effect of an antiferromagnetic molecular layer magnetically pinning an inorganic ferromagnetic layer through exchange bias has so far not been observed. We report on the magnetic interplay, extending beyond the interface, between a cobalt ferromagnetic layer and a paramagnetic organic manganese phthalocyanine (MnPc) layer. These ferromagnetic/organic interfaces are called spinterfaces because spin polarization arises on them. The robust magnetism of the Co/MnPc spinterface stabilizes antiferromagnetic ordering at room temperature within subsequent MnPc monolayers away from the interface. The inferred magnetic coupling strength is much larger than that found in similar bulk, thin or ultrathin systems. In addition, at lower temperature, the antiferromagnetic MnPc layer induces an exchange bias on the Co film, which is magnetically pinned. These findings create new routes towards designing organic spintronic devices.

Robust half-metallicity and topological aspects in two-dimensional Cu-TPyB

Half-metallicity due to the coexistence of metallic nature for one spin component and insulating nature for the other is a base of spintronics devices, but was only achieved in few materials. From first-principles calculations, we demonstrate that a recently-synthesized two-dimensional organometallic framework of 1,3,5-tris(pyridyl)benzene and Cu atoms (Cu-TPyB) has robust half-metallicity. High electron velocity in one spin channel at Dirac point and a relatively large band gap in the other make the material meeting the demand of filtering the current into a single spin component. Moreover, spin-orbit coupling induces topologically nontrivial band gaps in the vicinity of the Fermi level, which are implementable for achieving quantum anomalous Hall effect in a low temperature range (<8 K).

Controlling the Spin Texture of Topological Insulators by Rational Design of Organic Molecules

We present a rational design approach to customize the spin texture of surface states of a topological insulator. This approach relies on the extreme multifunctionality of organic molecules that are used to functionalize the surface of the prototypical topological insulator (TI) Bi2Se3. For the rational design we use theoretical calculations to guide the choice and chemical synthesis of appropriate molecules that customize the spin texture of Bi2Se3. The theoretical predictions are then verified in angular-resolved photoemission experiments. We show that, by tuning the strength of molecule-TI interaction, the surface of the TI can be passivated, the Dirac point can energetically be shifted at will, and Rashba-split quantum-well interface states can be created. These tailored interface properties-passivation, spin-texture tuning, and creation of hybrid interface states-lay a solid foundation for interface-assisted molecular spintronics in spin-textured materials.

Looking Inside the Perchlorinated Trityl Radical/Metal Spinterface through Spectroscopy

We report on a spectroscopic multitechnique approach to study the metal/radical spinterface formed by a perchlorinated trityl radical derivative and either gold or silver. The spectroscopic fingerprint of their paramagnetic properties could be determined by comparison with their diamagnetic precursor and by DFT calculations. Thanks to the presented approach, we could gain unprecedented insight into the radical-metal interaction and how this latter perturbs the spin polarization and consequently the magnetoelectronic properties of the radical adlayer. Knowledge of the factors influencing the spinterface is an essential tool toward the tailoring of the properties of spin-based electronic devices.

Unidirectional Spin-Dependent Molecule-Ferromagnet Hybridized States Anisotropy in Cobalt Phthalocyanine Based Magnetic Tunnel Junctions

Organic or molecular spintronics is a rising field of research at the frontier between condensed matter physics and chemistry. It aims to mix spin physics and the richness of chemistry towards designing new properties for spin electronics devices through engineering at the molecular scale. Beyond the expectation of a long spin lifetime, molecules can be also used to tailor the spin polarization of the injected current through the spin-dependent hybridization between molecules and ferromagnetic electrodes. In this Letter, we provide direct evidence of a hybrid interface spin polarization reversal due to the differing hybridization between phthalocyanine molecules and each cobalt electrode in Co/CoPc/Co magnetic tunnel junctions. Tunnel magnetoresistance and anisotropic tunnel magnetoresistance experiments show that interfacial hybridized electronic states have a unidirectional anisotropy that can be controlled by an electric field and that spin hybridization at the bottom and top interfaces differ, leading to an inverse tunnel magnetoresistance.

Local light-induced magnetization using nanodots and chiral molecules

With the increasing demand for miniaturization, nanostructures are likely to become the primary components of future integrated circuits. Different approaches are being pursued toward achieving efficient electronics, among which are spin electronics devices (spintronics). In principle, the application of spintronics should result in reducing the power consumption of electronic devices. Recently a new, promising, effective approach for spintronics has emerged, using spin selectivity in electron transport through chiral molecules. In this work, using chiral molecules and nanocrystals, we achieve local spin-based magnetization generated optically at ambient temperatures. Through the chiral layer, a spin torque can be transferred without permanent charge transfer from the nanocrystals to a thin ferromagnetic layer, creating local perpendicular magnetization. We used Hall sensor configuration and atomic force microscopy (AFM) to measure the induced local magnetization. At low temperatures, anomalous spin Hall effects were measured using a thin Ni layer. The results may lead to optically controlled spintronics logic devices that will enable low power consumption, high density, and cheap fabrication.

DEIMOS: a beamline dedicated to dichroism measurements in the 350-2500 eV energy range

The DEIMOS (Dichroism Experimental Installation for Magneto-Optical Spectroscopy) beamline was part of the second phase of the beamline development at French Synchrotron SOLEIL (Source Optimisée de Lumière à Energie Intermédiaire du LURE) and opened to users in March 2011. It delivers polarized soft x-rays to perform x-ray absorption spectroscopy, x-ray magnetic circular dichroism, and x-ray linear dichroism in the energy range 350-2500 eV. The beamline has been optimized for stability and reproducibility in terms of photon flux and photon energy. The main end-station consists in a cryo-magnet with 2 split coils providing a 7 T magnetic field along the beam or 2 T perpendicular to the beam with a controllable temperature on the sample from 370 K down to 1.5 K.