Molecular Spin Interactions in Magnetic Fields of Superconducting Vortices

Project Information

OPTIMISTIC

Grant agreement ID: 101109672

DOI

10.3030/101109672

Project closed

EC signature date 30 March 2023

Start date 1 February 2024

End date 31 January 2026

Funded under

• Marie Skłodowska-Curie Actions (MSCA)

Total cost

No data

EU contribution

€ 215 534,40

Coordinated by

AALTO KORKEAKOULUSAATIO SR
Finland

Periodic Reporting for period 1 - OPTIMISTIC (Molecular Spin Interactions in Magnetic Fields of Superconducting Vortices)

Reporting period: 2024-02-01 to 2026-01-31

Summary of the context and overall objectives of the project

Quantum technologies promise to transform computing and information processing, but their development depends on finding reliable building blocks — known as quantum bits, or qubits. Molecular spin systems are promising qubit candidates because they can be chemically engineered with precision and produced in large numbers. However, a key challenge is understanding how these molecular spins behave when exposed to strong magnetic fields, particularly fields that are highly localized at the nanometer scale.
The OPTIMISTIC project aimed to address this challenge by placing molecular spin systems onto the surfaces of superconducting materials. In certain superconductors, magnetic flux penetrates the material through tiny channels called Abrikosov vortices, each carrying exactly one quantum of magnetic flux. The magnetic field at the center of these vortices is extremely strong and confined to a region just a few nanometers wide — far smaller than what conventional magnets can achieve. This creates a unique laboratory for studying how molecular spins respond to intense, highly localized magnetic fields.
At the same time, the project aimed to harness this molecular spin sensing capability for a second purpose: investigating magnetism in atomically thin two-dimensional materials. Materials just one atom thick can exhibit exotic magnetic states — such as ferromagnetism or helimagnetic spirals — that are difficult to probe with conventional techniques. A magnetic molecule on the tip of a scanning probe microscope could serve as an ultrasensitive local probe of these magnetic states, opening new avenues for understanding and eventually exploiting 2D magnetism in future technologies.
The project had four main objectives: (1) upgrading the experimental equipment to enable new types of measurements, (2) mapping the magnetic field of vortices in high-temperature superconductors using a magnetic molecule attached to a scanning probe microscope tip, (3) studying how different molecular spin systems behave in these extreme local fields, and (4) applying the developed techniques to investigate magnetism in atomically thin two-dimensional materials. The fellowship was carried out at Aalto University, Finland.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

The project began with the development and testing of experimental tools. A method for fabricating antiferromagnetic microscope tips was successfully validated, and the design of a permanent magnet sample holder was completed. The main experimental work then focused on characterizing superconducting vortices using scanning tunnelling microscopy at temperatures close to absolute zero.
Initial experiments were performed on niobium diselenide (NbSe2), a well-known superconductor. The vortex lattice was imaged and two original protocols were developed for attaching a nickelocene molecule — a tiny magnetic sensor — to the microscope tip on superconducting surfaces. A key finding was that the magnetic field needed to observe the molecular sensor's response exceeded the field at which NbSe2 loses its superconductivity, making it unsuitable for the intended measurements.
This led to a strategic pivot toward bismuth strontium calcium copper oxide (BSCCO), a high-temperature superconductor that remains superconducting at much higher fields. A reliable procedure for preparing atomically clean BSCCO surfaces was established at the host laboratory, enabling the subsequent vortex field measurements. A new experimental protocol was established for probing vortex fields on BSCCO with the molecular sensor, and preliminary data confirm the detection of enhanced magnetic fields at vortex cores.
In parallel, work on two-dimensional magnetic materials led to an unexpected discovery: monolayer nickel dibromide (NiBr2) was found to be a multiferroic material — simultaneously exhibiting magnetic and electric order. This finding has been submitted for publication in a leading journal. Training and knowledge transfer activities included supervision of multiple student theses, teaching, conference presentations, and public outreach.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

The OPTIMISTIC project advanced the state of the art in several ways. The development of nickelocene tip functionalization protocols on superconducting substrates is a methodological first, enabling molecular-scale magnetic sensing directly on superconductor surfaces. The shift to BSCCO as the experimental platform required establishing sample preparation protocols at the host laboratory, which also benefited other ongoing projects in the group.
The preliminary detection of enhanced vortex magnetic fields through molecular Zeeman splitting on BSCCO represents progress toward the first direct, nanometer-resolution mapping of vortex magnetic fields — a measurement that has not been possible with any existing technique. If confirmed by the ongoing experiments, these results could reshape our understanding of the magnetic field structure inside superconducting vortices.
The discovery that monolayer NiBr2 is multiferroic opens a new direction in the study of two-dimensional materials, with potential relevance for future low-power electronic and spintronic devices. The molecular spin sensing methodology developed in this project is being applied to probe the magnetic ordering in this material, with further publications in preparation.
These results require further research to reach their full potential. The vortex field mapping experiments continue at the host institution with new sample batches, and the two-dimensional materials work is progressing toward comprehensive characterization. The techniques and protocols established during the project provide a foundation for future investigations by the host group and the broader research community.