Exploring long-range magnetism with graphene

Graphene is well known for its remarkable electronic properties. Now, researchers at INL have shown that it can also provide an exceptional platform for studying magnetism at the atomic scale, revealing magnetic interactions that extend across surprisingly long distances.

The research, carried out by INL researchers António Costa, João Henriques and Joaquín Fernández-Rossier, in collaboration with Universidad Autónoma de Madrid (UAM), provides new insight into how magnetic interactions behave at the smallest scales.

Magnetic interactions between spins are at the heart of many emerging quantum technologies, including quantum computing and quantum simulation. However, combining strong magnetic interactions with atomic-scale control remains a major challenge.

To tackle this problem, the team used a scanning tunnelling microscope to place individual hydrogen atoms onto graphene. Each hydrogen atom creates a localised magnetic moment, or spin, making it possible to build and study artificial magnetic structures with atomic precision.

Using advanced spectroscopy measurements and theoretical modelling, the team found that pairs of spins could interact strongly even when separated by more than 10 nanometres, revealing magnetic interactions that extend far beyond the distances typically observed in comparable atomically controlled systems. Depending on how the hydrogen atoms were arranged within the graphene lattice, the interactions could be either with spins aligning in the same direction (ferromagnetic), or with spins aligning in opposite directions (antiferromagnetic).

To better understand the experimental results, Rossier research group developed theoretical models capable of describing how these magnetic moments interact in graphene. The models helped interpret the observations and understand why these interactions remain strong over such long distances.

João Henriques adds: “This work shows how graphene presents itself as a unique platform to explore quantum magnetism. Graphene fragments have already been used to engineer molecular magnets in the past, and here we show how pristine graphene coupled with hydrogen generates unprecedented long range interactions, with the possibility of controlling them with atomic precision.”

The study, developed within the projects PiMag and FUNLAYERS, was recently published in the journal Nature Communications.

Spotlight by Catarina Moura, Clara Miranda, and Rui Andrade

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