Using a scanning tunneling microscope tip, defined electricity pulses were applied to the molecule, which switches between different magnetic states. Photo: CFN/KIT |
One
bit of digital information stored on a hard disk currently consists of
about 3 million magnetic atoms. Researchers from Karlsruhe, Strasbourg,
and Japan have now developed a mag-netic memory with one bit per
molecule. By an electric pulse, the metal-organic molecule can be
switched reliably between a conductive, magnetic state and a
low-conductive, non-magnetic state. This novel correlation for molecules
is now reported in the Nature Communications journal.
“The
superparamagnetic effect prevents smaller bit sizes from being reached
in a hard disk,“ explains Toshio Miyamachi, first author of the study
and researcher at the Center for Functional Nanostructures (CFN) of
Karlsruhe Institute of Technology (KIT). This super-paramagnetic effect
implies that magnetic memory crystals are in-creasingly susceptible to
thermal switching with decreasing size. Consequently, information may
soon be lost.
“We
chose another approach and placed a single magnetic iron atom in the
center of an organic molecule consisting of 51 atoms. The organic shell
protects the information stored in the central atom.” Apart from the
ultimate density of one bit per molecule, this type of memory based on
so-called spin crossover molecules also has the advantage of the
writ-ing process being reliable and purely electric.
“Using
a scanning tunneling microscope, we applied defined elec-tricity pulses
to the nanometer-sized molecule,” adds Wulf Wulfhe-kel, head of the
research group at KIT’s Physikalisches Institut. “This reproducibly
changes not only the magnetic state of the iron, but also the electric
properties of the molecule.” Hence, the two magnetic configurations lead
to varying conductances, such that the mag-netic state of the molecule
can be determined easily by a simple resistance measurement.
The
present study reports the fundamentals and shows the principle
feasibility and advantages of memories consisting of spin crossover
molecules. “These memristive and spintronic properties combined in a
molecule will open up a new field of research,” the researchers are
convinced. Memristors are memories that store information in the form of
resistance variations. Spintronics uses the magnetic spin of individual
particles for information processing.
Work
was carried out at the laboratories of the Center for Functional
Nanostructures (CFN) of KIT, the Institut de Physique et Chimie des
Matériaux (IPCMS) in Strasbourg, the SOLEIL synchrotron in Paris, and
the Chiba University, Japan.
Robust spin crossover and memristance across a single molecule
