Ultrafast Optical Control of Magnetism in Europium Chalcogenides: Phenomena and Mechanisms

Europium chalcogenides Eu X ( X = O, S, Se, and Te) represent a unique class of intrinsic magnetic semiconductors in which light can be used to directly control magnetic order on ultrafast time scales. This review synthesizes a series of pioneering magneto-optical phenomena in these materials, driven by their electronic structure: a valence band of highly localized 4f 7 spins and a conduction band of empty 5d states. Optical excitation across the bandgap dramatically enhances the exchange interaction between 5d electrons and the 4f spin lattice, triggering remarkable effects. We demonstrate how femtosecond laser pulses can initiate magnetization precession through the optical orientation effect, generate colossal magnetic polarons with moments exceeding 10 5 μ B , and enable coherent control over spin dynamics. These findings elucidate the fundamental principles behind ultrafast light–spin coupling, elevating europium chalcogenides to a model system for this class of phenomena. The uncovered mechanisms inform the search for material platforms where magnetism can be controlled at the high speed.