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Abstract:
*IMDEA Nanociencia researchers report the first encapsulation of
spin-crossover (SCO) molecules inside carbon nanotubes.*

·*SCO molecules present a radical spin change with temperature, relevant
for magnetic switches and spintronics devices. *

·*This is a fundamental research result that helps to understand the
behaviour of magnetic molecules confined in very small spaces.*

Scientists build the smallest cable containing a spin switch

Madrid and Sevilla, Spain | Posted on March 12th, 2021

A research work published in /Nature Communications/, involving
researchers from the Madrid Institute for Advanced Studies in
Nanoscience (IMDEA) and the University of Sevilla, has measured for the
first time the electrical conductivity of a single carbon nanotube with
spin-crosslinked molecules inside it.

As electronic devices continue to shrink to meet the demands of the
market, scientists are working to develop the minute components that
make them work. There is a persistent demand for fast and efficient
processes, and spin-logic (Spintronics) devices could be the solution to
shape the future of computing. Here, magnetic molecules could add a new
twist to conventional electronics. In particular, spin-crossover (SCO)
molecules conform a family of zero-dimensional (0D) functional units
that display a radical spin switch triggered by an electro-structural
change activatable by external stimulus such as light, pressure or
temperature. The spin switch confers SCO molecules excellent
capabilities and functionalities for implementation in nano-electronics.
However, their insulating character prevent these molecules to be fully
exploited so far. Several groups have embedded SCO molecules into
matrices of conductive material but the results are not fully compatible
with the requirements of nanoscale devices.

A ground-breaking system for effectively incorporating SCO molecules to
conductive materials is to introduce them inside conductive carbon
nanotubes. Carbon nanotubes are one-dimensional (1D) materials, strong,
lightweight and, most importantly, highly electrically conducting
miniature wires, typically 1-5 nanometres in diameter, but up to
centimetres in length. For the first time, a group of researchers at
IMDEA Nanociencia have encapsulated Fe-based SCO molecules inside carbon
nanotubes. The single-walled carbon nanotubes act as conducting
backbones that carry, protect and sense the SCO spin state of the
molecules, and overcomes their insulating drawbacks.

Iron-based SCO molecules encapsulated in a single carbon nanotube.
Credit: Nature Communications 2021.

The researchers, led by Prof. Emilio M. Pérez, Dr. José Sanchez Costa
and Dr. Enrique Burzurí, studied the electron transport through
individual carbon nanotubes embedded in nanoscale transistors by
dielectrophoresis. They found a change in the nanotube’s electrical
conductance that is modified by the spin state of the encapsulated SCO
molecules. The transition between the two conducting states is triggered
by a thermal switch that turns out to be not symmetric: the transition
temperature point is not the same going down than up the thermometer.
This fact opens a hysteresis not present in crystalline samples, and
many interesting potential applications for the hybrid system arise:
“These systems are like mini-memory elements at the nanoscale, as they
present a hysteresis cycle with temperature variation. They could also
serve as a filter of spin (a demand for spintronic devices) because the
nanotube “feels” if the molecule has spin or not” Dr. Burzurí comments.

The experimental results are supported by theory calculations by
researchers at Universidad de Sevilla. During the switching, the
orbitals of the SCO molecules change and hence their hybridization with
the carbon nanotube, that in turn modifies the electrical conductivity
of the latter. The SCO molecules in their low spin state have a stronger
interaction with the nanotubes; it is more difficult for them to change
their spin state and this is translated to a “jump” in the nanotube
conductivity at a certain temperature, depending on the initial spin state.

This first encapsulation of SCO molecules inside single-walled carbon
nanotubes is a fundamental research result that helps to understand the
behaviour of these molecules when confined in very small spaces, and
provides a backbone for their readout and positioning into nanodevices.
The authors hope that such mix-dimensional (0D-1D) hybrid can leverage
the best properties of their constituent materials, exploiting the spin
state as another degree of freedom. This miniscule wire and switch can
be produced on a preparative scale and may represent a relevant step in
the development of nanoscale magnetic systems.

This research outcome is the result of a collaboration amongst
researchers at IMDEA Nanociencia and Departamento de Química Física at
Universidad de Sevilla. Prof. Emilio M. Pérez is the leader of the Group
of Chemistry of Low Dimensional Materials; Dr. José Sánchez Costa is the
leader of the Group of Switchable Nanomaterials; Dr. Enrique Burzurí is
the leader of the group Functional Nanoscale Materials and Devices; all
three groups at IMDEA Nanociencia. The three main authors acknowledge
the funding from the Spanish Ministry of Science and Innovation and the
Severo Ochoa Excellence in R&D award to IMDEA Nanociencia (2017-2021).

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Contacts:
IMDEA Nanociencia
C/Faraday 9
28049 Madrid, Spain
Tel.: +34 91 299 87 00
www.nanociencia.imdea.org
Twitter: @IMDEA_Nano
Facebook: @IMDEANanociencia
Instagram: @IMDEANanociencia

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