In a recent open-access paper published in Nature Communications by researchers from the MIT Plasma Science and Fusion Center (PSFC), namely Hang Chi, Yunbo Ou, Jagadeesh Moodera, and their co-authors, an intriguing exploration of the possibilities presented by versatile magnets is presented. They investigated the “Strain-tunable Berry curvature in quasi-two-dimensional chromium telluride,” delving into the potential innovations that could arise from manipulating the physical properties of magnets.
To understand the significance of their discovery, we must go back in time to Edwin Hall’s 1879 experiment. He observed that when a magnet was placed at right angles to a strip of metal with an electric current passing through it, one side of the strip developed a greater charge than the other. This became known as the Hall effect, and back then, the understanding of physics was classical, where predictable and unchanging forces like gravity and magnetism governed matter.
However, as quantum mechanics emerged, scientists discovered that the Hall effect can also be observed without an external magnetic field, known as the anomalous Hall effect. Quantum mechanics can be likened to a car journey through a desert, where random events (like an armadillo crossing the road) cannot be predicted from a macro-level map (classical physics). Instead, quantum spaces have localized rules, and the “Berry phase,” named after physicist Michael Berry, acts like a GPS logger for the journey. It records the entire trip, revealing the curvature of the quantum landscape, which can shift electrons and induce the Hall effect even without an external magnetic field.
The authors of the paper focused on the “Berry curvature” and its relation to the anomalous Hall effect in a unique magnet made of thin layers of chromium telluride grown on crystal bases of aluminum oxide or strontium titanate. By squeezing or stretching these layers, they were able to manipulate the anomalous Hall effect and Berry curvature. Neutron scattering experiments conducted in collaboration with Oak Ridge National Laboratory (ORNL) provided valuable insights into the material’s chemical and magnetic properties.
The implications of this discovery are substantial. For instance, in the realm of data storage, strain-tunable materials like the ones studied could enable hard drives to store additional data in regions that have been stretched differently. Robotics could benefit from strain-tunable materials as precise sensors for feedback on movements and positioning, particularly in “soft robots” that mimic biological organisms. Additionally, magnetic devices that change behavior when bent or flexed could be used for environmental monitoring or highly sensitive health monitoring equipment.