Final Report Summary - SPINMOL (Magnetic Molecules and Hybrid Materials for Molecular Spintronics)
In this project we have designed new magnetic molecules and new classes of magnetic molecular materials which, conveniently nanostructured, have shown to be of interest in molecular spintronics, quantum computing and, in general, in nanomagnetism.
The project has covered the two major goals of this new field of research, namely the development of molecule-based materials with interesting spintronic properties (molecule-based spintronics), and the use of magnetic molecules in single-molecule nanospintronics and quantum computing.
Related with the former aspect (molecule-based spintronics), a major achievement has been the fabrication of the first molecular spin valves that emit light at low voltages. The idea behind these multifunctional devices, namely spin-OLEDs, is that of tuning the emitted light by applying an external magnetic field. We have shown that a suitable way to reach this goal is to fabricate a hybrid-LED structure in which the two metallic electrodes have been substituted by two ferromagnetic electrodes (Fe and Co, or LSMO and Co). In the same vein, a second key achievement has been the design, using a chemical approach, of new classes of multifunctional magnetic materials. It is worth to mention 1) the preparation of layered magnetic superconductors combining superconductivity and magnetism; 2) the preparation of nanocomposites formed by graphene and magnetic nanoparticles exhibiting unprecedented features in the capacitance and in the magneto-resistance properties, which can make them useful as hybrid supercapacitors; 4) The preparation of stimuli-responsive multifunctional materials formed by magnetic flexible metal-organic frameworks able to respond either to a physical stimulus (light) or to a chemical stimulus (reversible and selective sorption and release of gaseous molecules such as HCl or CO2). These ground-breaking discoveries have shown the power of chemistry to design unprecedented classes of nanostructured magnetic materials.
Related with the second aspect (molecular nanospintronics and quantum computing) a major goal has been to demonstrate that some theoretical proposals involving magnetic molecules may come true experimentally through the use of robust inorganic magnetic molecules. In this vein, we have exploited for the first time the structural and electronic versatilities of the polyoxometalate clusters to isolate new types of single-molecule magnets based on lanthanides, and to propose these molecules as spin qubits in quantum computing. This class of molecular metal-oxides has provided the unique opportunity to minimize the quantum decoherence effects in these spin qubits since they can be prepared free of nuclear spins. In this vein we have also demonstrated that, thanks to the electronic features of these clusters, the major sources of decoherence (dipolar interactions) in these solid-state molecular qubits can eliminated in an effective way without resorting to extreme magnetic dilution (this result will appear published in Nature). A second focus of interest has been the fabrication of electrically-controlled spintronic nanodevices formed by a single molecular nanoobject. This challenging goal is of current interest in spintronics. In this project the first attempts along this direction have been performed, not only from the theoretical point of view, but also from the experimental one. Thus, a ground-breaking result has been to demonstrate that a nanodevice formed by a single spin-crossover nanoparticle of 10 nm. size connected to two gold electrodes can undergo a crossover from the low-spin to the high-spin state under the application of an external electric field, or by a change in the temperature. Such a spin bistability can be monitored by measuring the electronic transport through the nanoparticle, which changes depending on its spin state. In fact, this molecular device constitutes the first spin memory operating near room temperature, in which a thermal and electric control over the molecular spin state can be achieved. Finally, a third relevant result has been to show that these magnetic nanoobjects can be positioned on a surface with a nanometric accuracy. This possibility has been demonstrated combining the top-down local oxidation nanolithography technique with a bottom-up chemical approach that takes advantage of the electrostatic interactions established between negatively charged nanoparticles and a positively functionalized patterned surface. For the first time we have shown that it is possible to place a single magnetic nanoparticle, based on bimetallic cyanide complexes on a silicon surface, with a nanometric accuracy and to investigate the magnetism of these single nano-objects by using a magnetic force microscope (MFM) operating at low temperatures. This last result has demonstrated that it is possible to observe and manipulate magnetic vortices in chemically-designed nanoparticles, a major advance with respect of the state-of-the-art in this topic, which restricted the observation of this type of magnetic structures to lithographically-designed micrometric size objects.
The project has covered the two major goals of this new field of research, namely the development of molecule-based materials with interesting spintronic properties (molecule-based spintronics), and the use of magnetic molecules in single-molecule nanospintronics and quantum computing.
Related with the former aspect (molecule-based spintronics), a major achievement has been the fabrication of the first molecular spin valves that emit light at low voltages. The idea behind these multifunctional devices, namely spin-OLEDs, is that of tuning the emitted light by applying an external magnetic field. We have shown that a suitable way to reach this goal is to fabricate a hybrid-LED structure in which the two metallic electrodes have been substituted by two ferromagnetic electrodes (Fe and Co, or LSMO and Co). In the same vein, a second key achievement has been the design, using a chemical approach, of new classes of multifunctional magnetic materials. It is worth to mention 1) the preparation of layered magnetic superconductors combining superconductivity and magnetism; 2) the preparation of nanocomposites formed by graphene and magnetic nanoparticles exhibiting unprecedented features in the capacitance and in the magneto-resistance properties, which can make them useful as hybrid supercapacitors; 4) The preparation of stimuli-responsive multifunctional materials formed by magnetic flexible metal-organic frameworks able to respond either to a physical stimulus (light) or to a chemical stimulus (reversible and selective sorption and release of gaseous molecules such as HCl or CO2). These ground-breaking discoveries have shown the power of chemistry to design unprecedented classes of nanostructured magnetic materials.
Related with the second aspect (molecular nanospintronics and quantum computing) a major goal has been to demonstrate that some theoretical proposals involving magnetic molecules may come true experimentally through the use of robust inorganic magnetic molecules. In this vein, we have exploited for the first time the structural and electronic versatilities of the polyoxometalate clusters to isolate new types of single-molecule magnets based on lanthanides, and to propose these molecules as spin qubits in quantum computing. This class of molecular metal-oxides has provided the unique opportunity to minimize the quantum decoherence effects in these spin qubits since they can be prepared free of nuclear spins. In this vein we have also demonstrated that, thanks to the electronic features of these clusters, the major sources of decoherence (dipolar interactions) in these solid-state molecular qubits can eliminated in an effective way without resorting to extreme magnetic dilution (this result will appear published in Nature). A second focus of interest has been the fabrication of electrically-controlled spintronic nanodevices formed by a single molecular nanoobject. This challenging goal is of current interest in spintronics. In this project the first attempts along this direction have been performed, not only from the theoretical point of view, but also from the experimental one. Thus, a ground-breaking result has been to demonstrate that a nanodevice formed by a single spin-crossover nanoparticle of 10 nm. size connected to two gold electrodes can undergo a crossover from the low-spin to the high-spin state under the application of an external electric field, or by a change in the temperature. Such a spin bistability can be monitored by measuring the electronic transport through the nanoparticle, which changes depending on its spin state. In fact, this molecular device constitutes the first spin memory operating near room temperature, in which a thermal and electric control over the molecular spin state can be achieved. Finally, a third relevant result has been to show that these magnetic nanoobjects can be positioned on a surface with a nanometric accuracy. This possibility has been demonstrated combining the top-down local oxidation nanolithography technique with a bottom-up chemical approach that takes advantage of the electrostatic interactions established between negatively charged nanoparticles and a positively functionalized patterned surface. For the first time we have shown that it is possible to place a single magnetic nanoparticle, based on bimetallic cyanide complexes on a silicon surface, with a nanometric accuracy and to investigate the magnetism of these single nano-objects by using a magnetic force microscope (MFM) operating at low temperatures. This last result has demonstrated that it is possible to observe and manipulate magnetic vortices in chemically-designed nanoparticles, a major advance with respect of the state-of-the-art in this topic, which restricted the observation of this type of magnetic structures to lithographically-designed micrometric size objects.