Abstract
In ferromagnetic materials, such as iron, cobalt, or nickel, the magnetic moments of the atoms are all ordered parallel, leading to a macroscopic net magnetization of the material. This magnetization can be reoriented between two directions at fast GHz rates, which is used to encode binary bits of information (0s and 1s) in hard disk drives (HDDs). Currently, more than half of the global digital data is stored this way. Unfortunately, the use of ferromagnets has hit its fundamental limits in terms of speed, stability, and power consumption. An alternative approach would be to use antiferromagnets, where the magnetic moments of neighbouring atoms are ordered antiparallel. These magnetic materials are more robust and up to thousands of times faster than ferromagnets. However, antiferromagnets do not immediately appear magnetic, making them notoriously difficult to control. Over the past years, it has become clear that using ultrashort pulses of light might be the fastest and most energy-efficient way to obtain control of antiferromagnets. This PhD thesis explores new methods to control the orientation of the atomic moments in antiferromagnets by creating and exploring new "coherent and non-equilibrium states" using ultrashort pulses of light.
