Being able to use antiferromagnets will make computer memory that is more energy efficient and smaller, faster with less corruption issues. Researchers at the Nanyang Technological University, Singapore (NTU Singapore) have discovered a new way of reading data in antiferromagnets. There were no practical methods to read data from antiferromagnets.
Computer memory traditionally comprises silicon microchips. But in the past few decades, researchers have been looking at using magnetic materials called ferromagnets, made from alloys of cobalt and iron, for memory chips, and that are now used in artificial intelligence and space applications. This is partly because ferromagnetic chips are more energy efficient than silicon ones.
Unique voltage solves data-reading problem
While studying the physical properties of a new antiferromagnetic material called manganese bismuth telluride, Assoc Prof Gao’s team stumbled on an observation that solved the data-reading problem.
They passed an alternating current through a very tiny device the size of a raindrop consisting of manganese bismuth telluride crystal flakes at extremely low temperatures of around 5 Kelvins or -268 degrees Celsius, which approaches the coldness of outer space.
They found a unique voltage signal across the crystals with a frequency double that of the alternating current. The scientists had expected the frequencies of the voltage and current to be the same.
They also found that depending on how the antiferromagnetic manganese bismuth telluride was configured, the sign of the voltage would change.
If the voltage was positive, it meant the antiferromagnet was in a state representing 0.
If the voltage was negative, the material was in a state representing 1. This observation solves the problem of not being able to easily read information stored in antiferromagnets.
Other antiferromagnets should display a similar behavior and their next step will be to test such materials that can encode data at room temperature.
The Berry curvature and quantum metric are the imaginary part and real part, respectively, of the quantum geometric tensor which characterizes the topology of quantum states. The former is known to generate a zoo of important discoveries such as quantum Hall effect and anomalous Hall effect (AHE) while the consequences of the quantum metric have rarely been probed by transport. Here we report the observation of quantum metric-induced nonlinear transport, including both nonlinear AHE and diode-like nonreciprocal longitudinal response, in thin films of a topological antiferromagnet, MnBi2Te4. Our observation reveals that the transverse and longitudinal nonlinear conductivities reverse signs when reversing the antiferromagnetic order, diminish above the Néel temperature, and are insensitive to disorder scattering, thus verifying their origin in the band structure topology. They also flip signs between electron and hole-doped regions, in agreement with theoretical calculations. Our work provides a pathway to probe the quantum metric through nonlinear transport and to design magnetic nonlinear devices.
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