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R&D: Nanomagnets for Future Data Storage

For development of miniature data storage devices

By Fabio Bergamin , ETH Zurich

An international team of researchers led by chemists from ETH Zurich have developed a method for depositing single magnetisable atoms onto a surface.

Dysprosium atoms (green) on the surface of nanoparticles
can be magnetised in only one of two possible directions:
‘spin up’ or ‘spin down’.

(Visualisations: ETH Zurich / Université de Rennes)


This is especially interesting for the development of new miniature data storage devices.

The idea is intriguing: if only a single atom or small molecule was needed for a single unit of data (a zero or a one in the case of binary digital technology), massive volumes of data could be stored in the tiniest amount of space. This is theoretically possible, because certain atoms can be magnetised in only one of two possible directions: ‘spin up’ or ‘spin down’. Information could then be stored and read by the sequence of the molecules’ magnetisation directions.

However, several obstacles still need to be overcome before single-molecule magnet data storage becomes a reality. Finding molecules that can store the magnetic information permanently and not just fleetingly is a challenge, and it is even more difficult to arrange these molecules on a solid surface to build data storage carriers. To address the latter problem, an international team of researchers led by chemists from ETH Zurich has now developed a new method that offers numerous advantages over other approaches.

Fusing atoms to the surface
Christophe Copéret, professor, Laboratory of Inorganic Chemistry at ETH Zurich, and his team developed a molecule with a dysprosium atom at its centre (dysprosium is a metal belonging to the rare-earth elements). This atom is surrounded by a molecular scaffold that serves as a vehicle. The scientists also developed a method for depositing such molecules on the surface of silica nanoparticles and fusing them by annealing at 400 degrees Celsius. The molecular structure used as a vehicle disintegrates in the process, yielding nanoparticles with dysprosium atoms well-dispersed at their surface. The scientists showed that these atoms can be magnetised and maintain their magnetic information.

Molecules with a dysprosium atom (blue) at their centre
are first deposited onto the surface of a silica nanoparticle (red and orange)
and then fused with it.

(Visualisations: Allouche F et al. ACS Central Science 2017)

The magnetisation process currently only works at around minus 270 degrees Celsius (near absolute zero), and the magnetisation can be maintained for up to one and a half minute. The scientists are therefore looking for methods that will allow the magnetisation to be stabilised at higher temperatures and for longer periods of time. They are also looking for ways to fuse atoms to a flat surface instead of to nanoparticles.

Simple preparation
One of the advantages of the new method is its simplicity. “Nanoparticles bonded with dysprosium can be made in any chemical laboratory. No cleanroom and complex equipment are required,” says Florian Allouche, doctoral student, Copéret’s group. In addition, the magnetisable nanoparticles can be stored at room temperature and re-utilized.

Other preparation methods include the direct deposition of individual atoms onto a surface, yet the materials obtained are only stable at very low temperatures mainly due to the agglomeration of these individual atoms. Alternatively, molecules with ideal magnetic properties can be deposited onto a surface, but this immobilization often negatively affects the structure and the magnetic properties of the final object.

For this research project, ETH scientists worked with colleagues from the Universities of Lyon and Rennes, France, Collège de France in Paris, France, Paul Scherrer Institute, Switzerland, and Berkeley National Laboratory in USA

Article : Magnetic Memory from Site Isolated Dy (III) on Silica Materials
ACS Central Science
has published an article written by Florian Allouche, Giuseppe Lapadula, Georges Siddiqi, Department of Chemistry and Applied Biosciences, ETH Zürich, Vladimir Prelog Weg 1-5, CH-8093 Zürich, Switzerland, Wayne W. Lukens, Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States, Olivier Maury, Univ Lyon, Ecole Normale supérieure de Lyon, Laboratoire de Chimie UMR 5182 CNRS—Université Claude Bernard Lyon 1—ENS Lyon, 46 Allée d’Italie, 69364 Lyon Cedex 07, France, Boris Le Guennic, Fabrice Pointillart, Institut des Sciences Chimiques de Rennes UMR 6226 CNRS-UR1, Université de Rennes 1, 35042 Rennes Cedex, France, Jan Dreiser,Swiss Light Source, Paul Scherrer Institute, CH-5232 Villigen PSI, Switzerland, Victor Mougel,Laboratoire de Chimie des Processus Biologiques, CNRS UMR 8229, Collège de France, Université Pierre et Marie Curie, 11 Place Marcelin Berthelot, 75231 Paris Cedex 05, France, Olivier Cador, Institut des Sciences Chimiques de Rennes UMR 6226 CNRS-UR1, Université de Rennes 1, 35042 Rennes Cedex, France, and Christophe Copéret, Department of Chemistry and Applied Biosciences, ETH Zürich, Vladimir Prelog Weg 1-5, CH-8093 Zürich, Switzerland.

Abstract : “Achieving magnetic remanence at single isolated metal sites dispersed at the surface of a solid matrix has been envisioned as a key step toward information storage and processing in the smallest unit of matter. Here, we show that isolated Dy (III) sites distributed at the surface of silica nanoparticles, prepared with a simple and scalable two-step process, show magnetic remanence and display a hysteresis loop open at liquid 4He temperature, in contrast to the molecular precursor which does not display any magnetic memory. This singular behavior is achieved through the controlled grafting of a tailored Dy (III) siloxide complex on partially dehydroxylated silica nanoparticles followed by thermal annealing. This approach allows control of the density and the structure of isolated, ‘bare’ Dy (III) sites bound to the silica surface. During the process, all organic fragments are removed, leaving the surface as the sole ligand, promoting magnetic remanence.

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