Spintronics research reveals that the magnetic state of certain materials can be changed using surface-induced stress.

Electronics is based on the transport of electrical charges from one place to another. Electrons move, current flows, and signals are transmitted by applying an electrical voltage. However, there is also another way to manipulate electronic currents and signals: by using the properties of spin, the intrinsic magnetic moment of the electron. This is called “spintronics” and has become an increasingly important area in contemporary electronics research.

An international research team involving TU Wien and the Czech Academy of Sciences has made an important breakthrough. They successfully reversed spins in an antiferromagnetic material using surface deformation. This could lead to an important new line of research in electronic technologies. The research is published in the journal Advanced functional materials.

“There are different types of magnetism,” explains Sergii Khmelevskyi from the Vienna Science Center Research Center, TU Wien. “The best known is ferromagnetism. It occurs when the atomic spins of a material are all aligned in parallel. But there is also the opposite, antiferromagnetism. In an antiferromagnetic material, neighboring atoms always have opposite spins .” Their effects therefore cancel each other out and no magnetic force can be detected from the outside.

“In 2010, however, scientists from TU Wien and the Czech Academy of Sciences came up with the idea that such antiferromagnetic materials had promising properties for spintronic applications,” says Khmelevskyi. This was the beginning of the new research field of “antiferromagnetic spintronics”, which has developed rapidly since.

Intensive work has been carried out recently by TU Wien, the Institute of Physics of the Czech Academy of Sciences and the Ecole Polytechnique (Paris). The biggest challenge was that the spins of antiferromagnetic materials are difficult to manipulate, but finding a way to manipulate them reliably and precisely is crucial. Only if magnetic states can be switched from one state to another in a targeted manner does it become possible to produce computer memory cells (e.g. MRAM).

Magnetic frustration: small effects make all the difference

Manipulating ferromagnets is simple: simply apply an external magnetic field to influence its internal magnetic properties. This is not possible with antiferromagnets, but there is a way out: you can work with surface deformations.

However, this requires very specific types of crystals. Depending on the geometry and arrangement of the atoms in the crystal, several different antiferromagnetic spin arrangements may be possible. The crystal adopts the state with the lowest energy. But it may be a situation where several different rotation orders have the same energy. This phenomenon is called “magnetic frustration”. “In this case, tiny interactions, which otherwise would not play any role, can decide the magnetic state of the crystal,” explains Khmelevskyi.

Experiments with uranium dioxide have shown that mechanical stress can be used to compress the crystal lattice just a little bit, which is enough to change the magnetic order of the material.

“We have now shown that antiferromagnets can actually be modified using the magnetic frustration properties existing in many known materials,” says Khmelevskyi. “This opens the door to many exciting developments in the direction of functional antiferromagnetic spintronics.”