Laser Pulse Flips Ferromagnet Polarity Without Heat in Groundbreaking Experiment

Scientists at ETH Zurich and the University of Basel have achieved a major breakthrough by using a short laser pulse to invert the magnetic polarity of a special ferromagnet, eliminating the need for heat. Traditionally, flipping a ferromagnet's polarity—like reorienting a compass needle—requires heating the material above its critical temperature to allow electron spins to realign before cooling. The team, led by Professors Ataç Imamoğlu and Tomasz Smolenski, accomplished this in a micrometer-sized sample made of twisted layers of molybdenum ditelluride, a moiré material that hosts robust topological states.

The experiment combines three pillars of modern condensed matter physics: strong electron interactions, topological properties, and light-based dynamical control. In this material, electrons form ferromagnetic order where spins align parallel in both insulating and conducting topological states. A single laser pulse reorients these spins collectively and permanently, with topology dictating the switching dynamics. Researchers confirmed the flip by measuring reflections from a weaker probe laser, revealing the new spin orientation.

This heat-free method enables repeated patterning of ferromagnetic regions, allowing dynamic control over topological properties. It matters for tech because it paves the way for optical writing of adaptable topological circuits on chips, potentially enabling tiny interferometers for detecting minute electromagnetic fields in precision sensing and quantum devices.

Looking ahead, the team aims to scale this to create arbitrary light-programmable circuits, revolutionizing spintronics and topological electronics with energy-efficient, ultrafast magnetic control.