| Jan 19, 2026 |
How a small molecule offers a new window into atomic-scale magnetism.
(Nanowerk News) A Czech and Spanish-led research team has demonstrated the ability to distinguish subtle differences between magnetic ground states using a new form of scanning probe microscopy.
|
|
In the last few years, a magnetic characterisation technique involving scanning tunnelling microscopy (STM) measurements with a magnetic nickelocene molecule has been developed. This technique provides insight into magnetic properties based on the interaction between nickelocene and a magnetic sample.
|
|
Led by researchers at FZU and at IMDEA Nanoscience, a new study (Journal of the American Chemical Society, “Magnetic Ground State Discrimination of a Polyradical Nanographene Using Nickelocene-Functionalized Tips”) uses nickelocene-based STM measurements to unambiguously discriminate between magnetic ground states of nanographene molecules, and to image their spin distribution at the atomic scale. The demonstration of these two properties show that this new technique is a powerful magnetic characterisation tool for unveiling the properties of correlated materials.
|
 |
| The interaction between the spin of a nickelocene (Nc) molecule at the apex of an STM probe with the spins of a magnetic nanographene molecule allow the molecule’s magnetic ground state to be determined. (Image: Courtesy of the researchers)
|
Mixing things up: extracting magnetic information with nickelocene
|
|
Measurements using STM involve the “jumping” of electrons between an atomically sharp metal probe and a sample of interest at sub-nanometre distances. At this proximity, when the apex of the probe is decorated with a nickelocene molecule, the nickelocene spin can interact with the spins of a magnetic sample resulting in a mixing of their magnetic properties (via a process called exchange-coupling). The strength of this effect can be carefully controlled by precisely varying the probe-sample distance.
|
|
The magnetic properties of nickelocene itself are well understood. So, by comparing the mixed magnetic properties of nickelocene and a magnetic sample to models, the authors can extract information about the magnetic properties of the sample itself.
|
|
“One of my favourite things about this project is that the key to the problem was finding a simple spin model,” explains first author Diego Soler Polo, who recently finished his role as a postdoctoral researcher in the Nanosurf Lab group at FZU and begun a position at IMDEA Nanoscience. “And not just a heavy ab initio simulation… although of course we also did that.”
|
|
In this study, the authors compared two nanographene molecules with almost identical structures. Nickelocene spectroscopy measurements revealed subtly different signatures for each molecule. This allowed the researchers to conclude that, despite their structural similarity, the molecules have different magnetic ground states.
|
 |
| Subtle differences in the experimental nickelocene (Nc) spectroscopy measurements (middle row) between the two structurally similar nanographene molecules (structures shown in top row) allowed the researchers to identify their distinct magnetic ground states (bottom row). (Image: Courtesy of the researchers)
|
A slice of the pi
|
|
The nanographene molecules in this study are examples of a class of magnetic materials known as π (pi)-magnets. Some carbon-based materials feature delocalised electrons within so-called π-states – such as the two possible arrangements of alternating double and single bonds in a benzene ring. Unlike conventional magnetic materials, whose magnetism arises from unpaired electrons in metal centres, π-magnets have spins which live within these delocalised π-states.
|
|
“π-magnets are a recent class of materials which are too reactive to stabilise using traditional chemical methods” explains corresponding author José I. Urgel, a group leader at IMDEA Nanoscience, “developments in synthetic protocols on-surfaces allowed for their synthesis for the first time – opening the door to this new field of magnetism.”
|
|
The nickelocene technique used by the authors is especially useful for studying π-magnets. Along with determining the magnetic ground state, it can also be used to image the spatial distribution of delocalised magnetic properties at the atomic scale.
|
 |
| Experimental measurements using a nickelocene molecule can also image the distribution of delocalised spins in the nanographene π-magnets. (Image: Courtesy of the researchers)
|
What’s next?
|
|
The demonstrated sensitivity to unique magnetic ground states and atomic-scale resolution makes the nickelocene a promising tool for characterizing correlated materials. As well as further characterisation of π-magnets, this technique might be able to shed new light on more exotic magnetic phases in 2D materials.
|
|
Urgel’s group at IMDEA, who are experts in π-magnetism, will continue to push towards new frontiers in these materials. As well as individual molecules, they will be working on π-magnetism in periodic structures which have the potential to be tuneable, flexible, and affordable platforms for realising quantum phenomena as the basis for new technologies.
|
