WG1. Organic Spintronics

Spin valves and magnetic tunnel junctions are at the core of spintronic applications. Typically, these spintronic devices involve sandwich trilayer nanostructures in which a non-magnetic material (metallic or insulating) is placed between two ferromagnetic electrodes. So far molecules are incorporated into these heterostructures as spacers, forming the intermediate layer situated in between the two ferromagnetic electrodes. The main achievements obtained in this context have been the discovery of several interface effects for strong and tunable interfacial spin selectivity (spinterface) in device heterostructures. On the other hand, the transfer of these effects into real applications is still hindered by the limited magneto-resistances achieved at room temperature and, generally, not sufficient reproducibility. Even more, controversies regarding the exact operation of these spin valves still exist; namely, whether the magneto-resistance response in this kind of structures is due to tunneling from one electrode to the other, or spin injection and diffusion in the molecular layer.

work needs to focus on a better understanding of spin-dependent transport phenomena through these molecular systems, including the spin-injection at the interface. To reach this first goal an engineering of the interfaces is required. A second challenging goal will be that of using molecule-based magnets as magnetic electrodes with the aim of fabricating an “all-molecular” spin valve. In this new kind of system the magnetoresistance properties may be improved thanks to the better matching in the conducting properties of the two components (the magnetic molecule-based electrode and the molecular semiconductor). A third goal is related with the design of new types of spintronic devices taking advantage of the multifunctional properties of the molecular materials. These multifunctional materials could offer unique possibilities for new device functions, since they would open the way to control the magnetization and the electrical resistance of the material by means of several external stimuli (electric field, light and/or pressure). The molecular approach might be a very versatile way to design this sort of materials since, through a wise choice of the molecular building blocks chemically engineered nanostructures having the desired combination of properties can be obtained. As multifunctional device, one must mention the spin-OLED as key example, a device in which the electroluminescence of the OLED will be controled through a magnetic field.

The associated research tasks to reach these goals can be summarized as follows:

T1.1. Chemical design of functional molecules and multifunctional molecular materials for spintronics.
T1.2. Interface engineering in organic spintronics.
T1.3. Integration of molecular materials into spintronic structures and fabrication of spintronic devices.
T1.4. Advanced physical characterization of the spintronic structures / devices.
T1.5. Theoretical modelling close to experiments and as a tool for design.

The key milestones are:

M1.1. Development of hybrid organic/inorganic materials featuring strong and tunable spin transfer efficiency at the interfaces.
M1.2. Fabrication of molecular spintronic devices with functionalities compatible with the high voltages required in molecular electronics applications.
M1.3. Control of the magneto-transport in molecular materials by means of external stimuli different from the electric and magnetic fields (light, pressure, chemical bistability).
M1.4. Realization of multifunctional electrically guided magnetic memories (R-MRAM) and magnetically guided electric memories (M-RRAM).

Working Group 1
Leader: Alek Dediu
Contact: v.dediu@bo.ismn.cnr.it

WG2. Single-Molecule Spintronics

A current trend in spintronics is to work in reduced dimensions with the aim of discovering new magnetic phenomena and to manipulate individual spins one by one. The study of the single nanoobjects connected to two magnetic electrodes has been limited to inorganic nanoparticles and organic carbon nanostructures. Although the transport through single molecules (or self-assembled molecular monolayers) has been extensively studied in molecular electronics, very few experiments have been reported so far in the case of magnetic molecules, or on magnetic nanoparticles based on molecules. Hence, the first goal of this WG will be the fabrication and study of electronic nanodevices based on magnetic molecules and other molecular nano-objects. Two methods are commonly used to perform such experiments: In one case, the molecule is connected through a STM tip and a conducting surface; the other case involves a single-molecule transistor architecture in which a break-junction entraps the molecule between two electrodes, while a third electrode acts as a gate. Still, many problems, which are intrinsic to the magnetic molecules, need to be solved to obtain reliable results. A first concern deals with the stability of these molecules when they are deposited on a metallic surface. In fact, most of the molecules of interest like single-molecule magnets (SMMs), for example, are coordination metal complexes that often undergo important structural and chemical changes when they are transferred from the solution to the surface. A second concern is that of positioning the magnetic molecule in a controlled manner and with a given orientation onto the surface (or in between the electrodes).

Assuming that these chemical and processing problems can be solved, the next goal will be that of fabricating nanodevices in which the molecular spins can be addressed. The experiments as well as the fundamental physics behind these devices remain largely unexplored and will be one of the main goals of this Action.

A final goal will be the fabrication of self-assembled ordered arrays of identical magnetic “dots” of the smallest size accessible –nanometer size– for their use in information storage devices. In this context, the use of self-organization processes for patterning technologies will be particularly appealing thanks to their low cost and high production efficiency.

The associated research tasks to reach these goals can be summarized as follows:

T2.1. Chemical design and physical characterization of molecular nanomagnets.
T2.2. Magneto-transport measurements and theoretical modelling across single molecules.
T2.3. Applications in nanospintronics.

The key milestones are:

M2.1. Realization of controllable and reproducible single molecule junctions.
M2.2. Spin addressing and manipulation of a single-molecule by electrical means.
M2.3. Spin addressing and manipulation of a single-molecule by scanning probe techniques.
M2.4. Scaling down the spintronic device to a single molecule.
M2.5. Development of a modelling tool set for addressing spin physics at the molecular level.

Working Group 2
Leader: Herre Van der Zant
Contact: H.S.J.vanderZant@tudelft.nl

WG3. Molecular spins for quantum technologies

Quantum technologies appears as a promising area in which magnetic molecules can be used not only for the storage of classical bits, but also for the creation, manipulation and readout of quantum superpositions of two spin states, thus providing realizations of spin qubits. The possible advantages of molecular spin systems in this context are the long quantum-coherence times they exhibit compared with semiconducting materials and the possibility of scalability either by arranging several qubits in a given molecule or by self-assembly processes. While coherent manipulation of single molecular qubits has been already demonstrated as well as spin entanglement at supramolecular level, effort is now concentrated on multi (two) qubit gates and on hybrid devices comprising molecular spins.

One of the issues to be addressed in this area is that of increasing the coherence time of the magnetic molecules. Application of error correction protocols imposes that gate operations must be 10^4 times faster than the rate at which qubits lose coherence (at present this figure of merit stands at 10^3). The couplings of the spins with the environment (phonons, nuclear spins, dipolar interactions) are important sources of decoherence, which are far from being understood and controlled. Still, via an appropriate chemical design of the molecule, some sources of decoherence (nuclear hyperfine and dipolar interactions) can be minimized. Furthermore, pulsed EPR experiments need to be performed in order to measure the decoherence parameters, together with theoretical calculations to account for the different mechanisms of decoherence.

A second important issue to be addressed is the search for new spin qubits architectures and the schemes for applying quantum information processing tasks. In this context the quantum behaviour of magnetic molecules is unique for the richness and variety of levels and states, and also for the wide possibilities to couple spins between them (entanglement), or with the external world (photons, electrons, nuclei, phonons). This issue involves strong theoretical and experimental efforts.

This WG will have strong interactions with WG2.

The associated research tasks to reach these goals can be summarized as follows:

T3.1. Chemical design of molecular spin qubits and qu-gates.
T3.2. Experimental and theoretical studies of the quantum coherence processes.
T3.3. Search for new spin qubits architectures and fabrication of quantum devices.

The key milestones are:

M3.1. Demonstration that magnetic molecules can be used for encoding multi-qubit gates.
M3.2. Definition of reliable procedures for preparing, characterising and positioning organized arrays of molecular spin qubits. Development of models and experimental setups for efficient coherent control and read-out.
M3.3. Realization of hybrid quantum devices including molecular spin.

Working Group 3
Leader: Fernando Luis Contact: fluis@unizar.es