Electrical tuning of magnetism in some exotic states of matter can lead to bizarre optical effects

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New Delhi, Aug 12 (PTI) Scientists have discovered that the electrical tuning of magnetism in certain exotic states of matter can lead to striking optical effects that are useful in certain optical devices, the Department of Science and Technology said Thursday.

They found that when an electric field is applied, electrons in the upper and lower layers of a special type of magnetic insulator called an anti-ferromagnetic axion insulator spontaneously deflect in opposite directions.

This property, called the Hall layer effect, allows the magnetism of these materials to be effectively controlled by an external electric field leading to electrical tuning of the magnetism with important applications in next-generation magnetic and optical devices.

Anti-ferromagnetic axion insulators are an exotic state of matter proposed decades ago, but remain experimentally elusive to this day. The manganese-bismuth telluride (MnBi2Te4) series of compounds has emerged as a promising class of anti-ferromagnetic axion insulators, and scientists are exploring its unique properties to use them in more innovative ways, the DST said.

A team from IIT Kanpur came across the “layer Hall effect” property in nanometer-thick devices made of manganese-bismuth telluride layers, he said.

The Hall effect refers to the generation of a transverse voltage in response to an electric field. It occurs in materials in the presence of a magnetic field.

More recently, it has been shown to occur even in the absence of a magnetic field, stemming from the “geometry” of electron movement in a crystalline solid in a paper published in the journal Nature.

The IIT Kanpur team led by Prof. Amit Agarwal experimentally observed a new type of Hall effect called the layer Hall effect, in which the top and bottom layers of the device generate cross current in opposite directions, which is made possible by a geometric property of the electron in crystals.

Moreover, the IIT Kanpur team observed that the magnetic state of MnBi2Te4 can be effectively switched by a coupled magnetic and electric field known as an axionic field.

This study, supported by the Science Engineering and Research Board (SERB) and the DST, opens the field to explore more exotic transport and optical effects in MnBi2Te4 using axionic electromagnetic coupling, the department said. PTI PR IJT

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