Magnets are crucial components in everything from electric motors and wind turbines to everyday items like speakers and smartphones. One of the key characteristics that determine a magnet’s performance is coercivity - the ability to resist being demagnetized. Materials with high coercivity, known as hard magnets, are highly sought after for applications requiring reliable permanent magnetism. These magnets are integral to renewable energy technologies, such as wind turbines and electric vehicle motors, which are pivotal for a sustainable future.

For example, while the magnets that hold your souvenirs on the fridge might seem strong, they are far from the hard magnets needed for heavy-duty tasks like running a powerful electric motor.

A Breakthrough in Magnet Technology

In the past, scientists have used various techniques to enhance the coercivity of ferromagnetic materials, such as adding rare-earth elements, modifying grain sizes, magnetic anisotropy engineering, or surface and interface modifications. However, these methods often involve complex processes or come with trade-offs, such as weakening the material or increasing costs.

In a surprising twist, the researchers at the University of Augsburg discovered that simply applying moderate pressure along one axis of the material CeAgSb₂ - classified as a soft quasi-two-dimensional ferromagnet - can significantly increase its coercivity, effectively transforming it into a hard magnet.

“This method is strikingly simple, yet it has never been reported before,” said Dr. Bin Shen, an Alexander von Humboldt Postdoctoral Fellow at the University of Augsburg. “It’s fascinating how such a straightforward approach can have such a dramatic effect."

How Does It Work? The Role of Defects

The key to this transformation may lie in the introduction of defects into the material when uniaxial stress is applied. These defects play a crucial role by pinning the magnetic domain walls - the boundaries between different magnetic regions within the material. This pinning effect increases the material’s coercivity, making it more resistant to demagnetization.

However, there’s a delicate balance: while some defects are necessary to pin domain walls and enhance coercivity, too many defects can disrupt the material’s magnetic order. This can weaken the magnet’s overall structure and compromise its effectiveness. And it’s not just the number of defects that matters - the type of defect is equally important. The researchers suspect they may have discovered a very special type of defect that is exceptionally effective at pinning domain walls while leaving other magnetic properties largely unaffected.

“We don’t yet know exactly what kind of defect we’ve introduced,” explains Dr. Anton Jesche, leader of the research group at the Chair of Experimental Physics VI. “But whatever it is, it appears to strike an ideal balance between enhancing coercivity and preserving the material’s structural integrity. Understanding these defects in greater detail will be a key focus of future research.”