Spintronics with chemically-prepared magnetic nanoparticles – CHEMISPIN

Chemical synthesis has shown its ability to elaborate magnetic nano-objects with high-quality magnetic properties, either under the form of molecules, or of nanoparticles (NPs) with well-controlled properties. These objects already play a major role in several actual technology fields (MRI,magnetic separation,hyperthermia,microwave), or are expected to do it soon (magnetic recording,bio-detection). They are moreover model objects for fundamental research. In spintronics, the use of magnetic NPs (MNPs) or magnetic molecules is expected to unveil a novel kind of physics and devices with innovating properties. For all those potential applications there is a strong need for a deep fundamental understanding of individual magnetic NP properties. Outstanding pioneer results in this direction have been obtained using the unique micro-SQUID magnetization probe. Another way is to electrically connect the single MNP to ferromagnetic electrodes. The main advantage is that while allowing the characterization of a single nano-object down to less than 2 nm, one would also be able to start to manipulate the magnetic nano-object: in the case of a MNP, spin currents will switch its magnetization, leading to oscillators based on steady-state precession; in the case of a magnetic molecule, this would open the way to precession up to 100 GHz and to the promising field of molecular spintronics. The use of chemically-synthesized MNPs (CSMNPs) will provide a unique way to control at the same time the nature, size, shape and anisotropy of the NPs which is necessary for fundamental studies. However, while appealing, this way is quite demanding. Hence, the natural marriage of MNPs to spintronics has not been very fruitful up to now. As a simple but revealing example, no results have been reported so far concerning the proven connection of an isolated MNP to ferromagnetic electrodes. The only few steps accomplished towards this direction were scarce and the product of well-known European and US leading teams (Cornell, TUDelft, Georgiatech and partner 3): an isolated Co MNP or Mn12 molecular magnet connected to non magnetic electrodes and non magnetic Au or Al NP and C60 connected to ferromagnetic electrodes. In each case, the mastering of a cutting-edge technology to contact a nano-object has been a decisive ingredient. As a matter of fact, ideal objects for the first fundamental studies of CSMNPs in spintronics would be composed of magnetic core surrounded by a thin oxide layer. From the chemistry point of view, the synthesis of such objects is a real challenge and a hot topic, which is pursued by several teams in order to use CSMNPs in biomedical, microwave or permanent magnet applications. Requirements in spintronics are probably the most drastic: the magnetic surface of the NPs must be covered by a thin homogeneous defect-free non-magnetic oxide layer below 3 nm without any degradation or oxidation of the underlying magnetic core. Several chemical approaches to protect CSMNPs have been reported, but they are often based on a controlled oxidation of the magnetic core leading to a passivated magnetic oxide layer, or indirectly lead to a partial oxidation of the magnetic core, and thus inadequate for spintronics. The objectives of the present project are i) the chemical synthesis of a thin inorganic tunnel barrier around CSMNPs, ii) their integration in innovative spintronics single-NPs devices, iii) the electrical characterization of their intrinsic properties (magneto-Coulomb effects) and the electrical manipulation of their magnetization (Spin 'Transfer Torque). Given its ambition, achieving this project requires a multi-disciplinary consortium extremely competitive at the international level and mastering key know-how. Partner 2 has a world-recognized competence on the elaboration of CSMNPs and recently deposited a patent on their protection by a thin oxide layer. Partner 3, in addition to be one of the world-leading laboratory in spintronics, is today among the few laboratories which routinely masters a technique to connect singles-nanoparticles; it has recently demonstrated the first observation of a ferromagnetic single-electron transistor driven by magneto-Coulomb effects on a non magnetic metallic NP. Partner 1 has been working in close collaboration with chemists on the magnetism of CSMNPs for more than 10 years and recently demonstrated the transport measurement on assemblies of CSMNPs synthesized by partner 2. At the present day, the only potential competitors to this project are found in the U.S.A.: Ralph's group at Cornell and Davidovic's one at Georgiatech. The success of this project would open the way of the bottom-up approach in zero-dimension spintronics. It would permit the experimental studies of several new fundamental effects and ideas which are so far only found in theoretical works. Finally, it could have large impacts in many fields ranging from magnetic recording to bio-medical applications of CSMNPs.