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A strange new magnetoelectric effect has been discovered in a symmetrical crystal



Magnetism and electricity are linked in many strange and wonderful ways in science, including the fascinating magnetoelectric effect that can be felt in some crystals – where the electrical properties of a crystal can be influenced by a magnetic field and vice versa.

Now it’s gotten even stranger because scientists discovered a brand new magnetoelectric effect in a symmetrical crystal – and that shouldn’t be possible.

The effect was found in a specific type of crystal called langasite, which is made up of lanthanum, gallium, silicon, and oxygen, as well as holmium atoms.

It is important that this particular crystal has a symmetrical structure, which is supposed to exclude the possibility of a connection between magnetism and electricity.

“Whether the electrical and magnetic properties of a crystal are coupled or not depends on the internal symmetry of the crystal,”

; says physicist Andrei Pimenov from the Vienna University of Technology (TU Vienna) in Austria.

“If the crystal has a high degree of symmetry, for example if one side of the crystal is exactly the mirror image of the other side, then for theoretical reasons no magnetoelectric effect can occur.”

In this case it was different: the symmetrical crystal could not only produce a magnetoelectric effect, but was also an effect not seen before.

Scientists say that while symmetry was maintained in a geometric sense, the magnetism of the holmium atoms broke the symmetry and allowed an effect that went into the realm of quantum physics.

This interruption meant that a polarization was possible in which the positive and negative charges in the crystal were shifted slightly.

This can easily be done using an electric field, but with langasite it can also be done using a magnetic field and the key is the strength of the magnetic field.

“The crystal structure is so symmetrical that it shouldn’t actually allow any magnetoelectric effect,” says Pimenov. “And with weak magnetic fields there is actually no coupling with the electrical properties of the crystal.”

“But when we increase the strength of the magnetic field, something remarkable happens: the holmium atoms change their quantum state and gain a magnetic moment. This breaks the internal symmetry of the crystal.”

While langasite showed a linear relationship between polarization and magnetic field strength, which is normal, the relationship between polarization and the direction of the magnetic field was not normal at all – it was highly non-linear.

This is the brand new aspect that even a small change in the rotation of the magnetic field can cause a large change in the electrical polarization effect.

The next step for the researchers is to see whether this newly discovered effect also works in the opposite direction and changes the magnetic properties through an electric field.

This may seem like a lot of high-end physics – and it is – but there are real world applications for storing and storing computer data. The magnetoelectric effect is also important for various types of sensor technologies.

“Magnetic fields are required in magnetic storage media such as computer hard drives today,” says Pimenov.

“They are generated with magnetic coils, which requires a relatively large amount of energy and time. If there was a direct way to replace the magnetic properties of a solid-state memory with an electric field, this would be a breakthrough.”

The research was published in NPJ quantum materials.


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