Researchers exceed data storage density limit
The use of spin crossover molecules as the smallest storage unit would make it possible to further increase the storage density of data carriers. The challenge is to attach these molecules to surfaces without destroying their storage capacity. A research team from the Christian-Albrechts-University of Kiel (CAU) has now succeeded in doing so. Not only did it successfully launch a new class of spin crossover molecules on a single surface, but it has also been able to exploit interactions that were previously considered obstructive to increase their storage capacity. In theory, this would increase the storage density of conventional hard disks by more than a hundred times and significantly reduce the size of data carriers.
Today, a bit on the hard disk only takes up an area of about 10 x 10 nanometers. However, this is still too large to keep pace with the increasing miniaturization of electronic components. The technology currently used in hard disks for data storage meets a quantum mechanical fundamental limit in the size of a bit. From today’s perspective, it cannot achieve further miniaturization, “says Torben Jasper-Tönnies, PhD student in the research group of Professor Richard Berndt at the Institute for Experimental and Applied Physics at CAU. The solution: he and his colleagues are using a single molecule as an example to demonstrate a principle that could enable even smaller hard disks with larger storage capacity in the future. The molecule is only one square nanometer in size. You could already use a 100 times smaller area to store a bit. From the perspective of the Kiel researchers, this would be a step towards shifting the quantum physical limits in storage technology. The interdisciplinary research team uses a molecule that can not only be switched between a high and a low magnetic state. Attached to a special surface, it can also be rotated by 45 degrees. Transferred to storage technology, this would allow us to map information to three states, i. e. 0,1 and 2,”explains Jasper-Tönnies. As a storage unit, we would not have a bit but a’ trit’, so the binary would become a’ trinary code’.
The scientists’ challenge was to find a suitable molecule as well as a suitable surface and to combine both with the right method. Magnetic molecules, so-called spin crossover molecules, are very sensitive and can be easily destroyed. The researchers therefore had to find a way to fix the molecule firmly on the surface and at the same time maintain its switching characteristic. The chemists from the research group led by Professor Felix Tuczek at the Institute of Inorganic Chemistry at CAU produced a magnetic molecule of a special class (a so-called iron (III) spin crossover molecule). This molecule could easily be bonded to a copper nitride surface by vapor deposition.
It is not only possible to switch between different spin states, but also (in the so-called “low spin” state) between two different orientations. The fine tip of a scanning tunneling microscope (RTM) performs the function of the read/write head in the hard disk. With its help, the molecule can not only be written to as a storage medium, but can also be read out via electricity. The principle applicability of the molecules as data storage devices was demonstrated with the aid of a scanning tunneling microscope. However, before these molecules can really be used as data storage devices for the industrial market, there is still an important hurdle to be overcome: it must be clarified how the molecules can be integrated into a chip.
The acehievement was published first the Nano Letters magazine under the title “Robust and Selective Switching of an Fe III Spin-Crossover Compound on Cu2N/Cu (100) with Memristance Behavior. Nano Letters 2017 17 (11), 6613-6619, DOI: 10.1021/acs. nanolett. 7b02481 “.