IISc research points to new era of quantum devices

Researchers at the Indian Institute of Science (IISc) may have found a way to develop compact and energy-efficient electronic devices that can store information, perform calculations and even connect with future quantum computers. The breakthrough comes from a new method developed by the researchers to use electric current to switch a material between two different magnetic states. Published in Nature Communications, the work was led by Bhagwati Prasad, Assistant Professor in the Department of Materials Engineering, together with first author Suryakanta Mondal, PhD student, and a team of national and international collaborators.

Many magnetic memory technologies rely on changing the direction of a material’s magnetisation. In this study, however, instead of simply flipping the direction of magnetisation, the team used an electric current to completely transform the material from one magnetic state to another. The researchers studied a complex oxide which is known for hosting multiple magnetic states. “Our initial motivation was to understand whether the closely competing magnetic states could be controlled directly using an electrical current,” explained Mondal.

At low current, the material exists in a ferromagnetic state in which its atomic magnetic moments are largely aligned in the same direction. In this state, electric current flows easily, and resistance is low. But when the applied current crossed a critical value, the material abruptly switched to an antiferromagnetic-like state in which neighbouring magnetic moments tend to point in opposite directions. This state has much higher electrical resistance. The team demonstrated that this electrically-driven transition is reversible and is accompanied by the collapse of long-range ferromagnetic order and a rearrangement of the material’s electronic orbitals. This makes the switch different from ordinary heating or conventional current-driven reversal of magnetisation. “What is fundamentally new is that the electric current does not merely rotate the magnetisation; it changes the magnetic phase of the material itself. This gives us two clearly distinguishable resistance states that may be useful for cryogenic memory and logic technologies,” said Prasad.

The researchers then used the material to fabricate nanoscale tunnel devices measuring about 250 by 250 nanometres in size. These miniature devices displayed two stable resistance states, with magnetoresistance exceeding 200 per cent. The switching could be controlled by electric current, temperature and magnetic field. Because the effect is strongest at low temperatures, the discovery is particularly promising for cryogenic memory and logic circuits that can support quantum computing platforms, which typically operate at extremely low temperatures.

The researchers now plan to work on reducing the current and energy required for switching, adapting the device for a wide range of operating temperatures. This could potentially lead to a new generation of low-power electronic and quantum devices.