Speaker
Description
Antiferromagnets are promising for spintronics and ultrafast data storage. While femtosecond lasers efficiently quench antiferromagnetic (AFM) order, demagnetization timescales in AFM insulators vary dramatically from picoseconds to nanoseconds. The mechanism behind this variability remains poorly understood. Here, we report the ultrafast melting of AFM order in the insulator Cr$_2$O$_3$ compared to the isostructural compound FeBO$_3$. We observe a 100-fold difference: FeBO$_3$ demagnetizes on a sub-nanosecond scale, whereas Cr$_2$O$_3$ exhibits rapid demagnetization in under 2 ps. Furthermore, we show this naturally fast process in Cr$_2$O$_3$ can be accelerated even further by thermally driving the system above its Néel temperature. Using first-principles calculations and atomistic spin-lattice dynamics, we trace this disparity to how ionic displacements modify spin interactions. The Heisenberg exchange striction in Cr$_2$O$_3$ is ten times stronger than in FeBO$_3$. We identify spin-lattice coupling strength as the decisive factor dictating AFM demagnetization timescales, offering a pathway to design faster memory devices.