This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Researchers in the U.S. and China have created a biocompatible, metal-free magnet that can be safely implanted and generate signals from deep inside the body. Led by Wubin Bai at the University of North Carolina, the team revealed how magnetism can emerge from the rearrangement of atoms in heated carbon nitride, which strengthens the coupling between unpaired electrons.
Published in Nature Materials, their research could lead to new types of wireless sensors that provide valuable medical data, without any need for potentially harmful radiation. Magnetic fields are ideally suited to medical monitoring. With their ability to penetrate deep into living tissue and track the real-time movements of organs wirelessly, techniques including MRI are now routinely used to create detailed medical images without subjecting the body to ionizing radiation.
But as Bai explains, the approach has so far proven far less suitable for wearable or implantable sensors. "Conventional strong magnets usually contain metals that can corrode or remain in the body, while metal-free magnets have generally been too weak for reliable sensing through tissue," he says. In metals such as iron, magnetism arises when the magnetic moments of unpaired electrons are locked into a strong, long-range alignment.
While this behavior can also emerge in metal-free compounds, the coupling between their unpaired electrons is generally far weaker. Ultimately, this means that the alignment is easily disrupted, leaving these materials only weakly magnetized once they are removed from an external magnetic field. Yet through their previous research, Bai's team uncovered an effect which appeared to upend this trend.
When carbon nitride is heated to temperatures of several hundred degrees, they found that it produces a tiny amount of magnetically attracting residue. To investigate the effect, Bai's team studied the material using a combination of advanced analytical techniques. The observations revealed that the heating had removed some nitrogen atoms from the compound, leaving behind sites which could host unpaired electrons.
At the same time, the reshaping of the compound's atomic layout introduced a new type of bonding structure, creating pathways that enabled these electrons to couple together. As a result, the alignment of their magnetic moments could persist even after the material was removed from an external magnetic field. Building on this discovery, Bai's team created their magnet from heat-treated graphitic carbon nitride: a semiconductor made from stacked 2D layers, best known for its use in absorbing visible light.
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