Spin manipulation and detection at the single-molecule scale

Towards a new concept of device in molecular spintronics

July 12, 2023

Achieving size-compact and energy-efficient control and detection of magnetism are paramount for the development of future spintronic devices. Using single molecules as quantum units opens a new pathway to reach the physical limits of miniaturization. However, due to the very large number of possible material combinations, there is an urgent need for fundamental understanding and guiding concepts to search for new smart, functional molecular designs. A novel concept has been proposed, enabling all-electrical spin manipulation and detection in molecular spinterfaces.

“Smaller, faster, lower energy consumption” are some of the keywords for next-generation information and communication technologies. Currently, spintronics devices are mainly operated via either an external magnetic field (e.g., tunnel magnetoresistance devices), which is high power consumption.


Figure 1: (a) Schematic view of a single FeTPP absorbed in substituted graphene with an STM tip and a back-gate plane. The proposed three-terminal device allows an out-of-plane and an in-plane transport. (b) The molecular spin states can be reversibly switched between S=1 and S=3/2 via a simple gate voltage. (c) The absorption of the molecule on BG changes the quantum transport behavior of the BG sheet dramatically from nonmagnetic to magnetic, which can be easily read out as “0” and “1”. 

Researchers from CEMES-CNRS associated with physicists from the Technical University of Denmark and SPEC-CEA theoretically (i.e., ab initio + quantum transport theory) proposed a new way to achieve a full-electrical control of molecular spintronic devices without relying on external magnetic fields. An experimentally feasible three-terminal quantum transport setup (see Fig. 1a) is proposed, where an iron porphyrin (FeTPP) molecule is deposited on B-doped graphene (BG). Notably, a reversible spin switching between S=1 to S=3/2 spin states is achieved by a gate voltage, tracing their origin to a strong hybridization between Fe-dz2 and B-pz orbitals due to perfect orbital symmetry-matching as shown in Fig. 1b.

These results show a “writing” operation at the atomic scale. The authors further demonstrate how the in-plane quantum transport for the BG, which is non-spin polarized, can be modified significantly by FeTPP, yielding a significant transport spin polarization near the Fermi energy (>10% for typical coverage, see Fig. 1c). Such a large spin-polarized signal can be probed by current state-of-the-art experimental techniques such as shot noise measurements. These complementary results show that it is, therefore, not only possible to write but also to read the spin.

The novel concept proposed in this work outlines both a general and an effective design principle required for successful all-electrical operations of molecular spintronic devices. This work could lead to the development of next-generation spintronic devices with ultralow-power consumption.

Proposal for all-electrical spin manipulation and detection for a single molecule on boron substituted graphene
F. Gao, D. Li, C. Barreteau, and M. Brandbyge
Phys. Rev. Lett. 129, 027201 (2022)

Dongzhe Li dongzhe.li[at]cemes.fr

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