The mystery of the Hall effect in a Weyl antiferromagnet unveiled

An advance in the use of antiferromagnetic materials in memory storage devices.

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Antiferromagnets have internal magnetism produced by electrons’ spin. However, these materials have no external magnetic field, meaning there is enough space to pack data units – bits densely; hence, they are a topic of interest because of their potential for data storage.

The property measured to read out an antiferromagnetic bit is called the Hall effect, which is a voltage that appears perpendicular to the applied current direction. The Hall voltage changes sign when the antiferromagnet’s spins are entirely flipped. As a result, the Hall voltage has two signs, one corresponding to a “1” and the other to a “0”. 

Although scientists have known about the Hall effect in ferromagnetic materials for a long time, the impact in antiferromagnets has only been recognized in the past decade and is still poorly understood. 

Now, A team of researchers at the University of Tokyo in Japan, Cornell and Johns Hopkins Universities in the USA, and the University of Birmingham in the UK have suggested an explanation for the ‘Hall effect’ in a Weyl antiferromagnet (Mn3Sn). This material has a particularly strong spontaneous Hall effect.

Mn3Sn is not perfectly antiferromagnetic but has a weak external magnetic field. Researchers were keen to determine if this weak magnetic field was responsible for the Hall effect.

Their study used a device to apply tunable stress to the tested material. By applying this stress to this Weyl antiferromagnet, they observed that the residual external magnetic field increased.

The voltage across the material would change if the magnetic field were driving the Hall effect. The researchers demonstrated that the voltage does not vary significantly, demonstrating that the magnetic field is insignificant. They concluded that the Hall effect is caused by how spinning electrons are arranged within the material.

Dr. Clifford Hicks at the University of Birmingham said“These experiments prove that the Hall effect is caused by the quantum interactions between conduction electrons and their spins. The findings are important for understanding – and improving – magnetic memory technology.”

Journal Reference:

  1. Ikhlas, M., Dasgupta, S., Theuss, F. et al. Piezomagnetic switching of the anomalous Hall effect in an antiferromagnet at room temperature. Nat. Phys. (2022). DOI: 10.1038/s41567-022-01645-5
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