Researchers show how to actively change magnetism through pressure

The development of magnetism depends on the behavior of electrons. For example, elementary particles can use their electric charges to generate electric currents, thereby inducing magnetic fields. However, magnetism can also arise through the collective arrangement of magnetic moments (spins) in a material. However, it has so far been impossible to continuously change the type of magnetism in a crystal.

An international research team led by Professor Andrej Pustogow of the Technical University of Vienna has now succeeded in doing just that: changing magnetism “at the push of a button”. To do this, the team continuously changed the magnetic interactions in the single crystal by applying pressure.The researchers recently published their findings in Physical Review Letters.

People have been fascinated by magnetism for thousands of years, and it first made many technological applications possible. From compasses to electric motors to generators, these and other devices would not exist without ferromagnetism.

Although ferromagnetism has been well studied, fundamental research is increasingly interested in other forms of magnetism. These are of particular interest for secure data storage and as potential platforms for quantum computers. “However, finding new forms of magnetism and completely controlling them is an extremely difficult endeavour,” said study leader Andre Pustogo.

Spins can be thought of as little compass needles that align themselves in an external magnetic field, as well as having a magnetic field themselves. In the case of ferromagnetism for permanent magnets, all electron spins are aligned parallel to each other. In certain arrangements of electron spins, such as in an ordinary square, checkerboard lattice, an antiparallel arrangement of spins is also possible: adjacent spins always point alternately in opposite directions.

For a triangular lattice (or a lattice in which a triangular structure occurs, such as the more complex Kagome lattice), a completely antiparallel arrangement is not possible: if two corners of the triangle have opposite spin directions, the remaining sides must be aligned with Match in one of the two directions. The two options, Rotate Up or Rotate Down, are exactly the same.

“This possibility of having multiple identical alternatives is called ‘geometric frustration’ and occurs in crystal structures where the electron spins are arranged in a triangle, kagome or honeycomb lattice,” explains solid-state physicist Pustogo. .” As a result, randomly arranged pairs of spins are formed, some of which find no partners at all.

“The remaining unpaired magnetic moments could potentially become entangled and manipulated by external magnetic fields for use in data storage or computational operations in quantum computers,” Pustogo said.

“In real materials, we are still far from this ideal frustrated state. First, we need to be able to precisely control the symmetry of the crystal lattice and thus the magnetism,” Pustog said. Although materials with strong geometric frustration can already be produced, a continuous change from weak to strong frustration and vice versa is not yet possible, especially within the same crystal.

To change the magnetism of the materials they studied “at the push of a button,” the researchers put the crystals under pressure. Starting with the Kagome structure, the lattice deforms due to uniaxial stress, changing the magnetic interactions between electrons.

“We use mechanical pressure to force the system into the preferred magnetic orientation. Sometimes in real life, pressure can reduce frustration because we are forced to make a decision that we don’t have to make ourselves,” Pustogo said.

The team successfully increased the magnetic phase transition temperature by more than 10%. “This may not seem like a big deal at first, but if the freezing point of water increased by 10 percent, it would freeze at 27 degrees Celsius, which would have serious consequences for the world as we know it,” Pustogo explained.

While in the current case mechanical pressure reduces geometric frustration, the team now aims to increase frustration to completely eliminate antiferromagnetism and achieve quantum spin liquids as described above. “The possibility of actively controlling geometric frustration through uniaxial mechanical stress opens the door to unexpected manipulation of material properties at the push of a button,” Pustogo said.