Abstract
A hard disk drive (HDD) stores information in the form of small magnetic areas magnetized in opposite directions, like tiny bar magnets pointing north or south. Depending on the orientation of these bits the information can be later retrieved as 'ones' and 'zeros'. The conventional way to reverse a magnetic bit is by applying a magnetic field pulse. Although today a HDD stores a magnetic bit in ~1 nanosecond, the speed of this process was expected to be as high as desired, provided that sufficiently high fields would be available. However, it was recently predicted that no matter how short and strong the magnetic field pulse is, there is a natural limit of switching the magnetic bit on the picosecond time scale, beyond which magnetization reversal becomes chaotic [I. Tudosa et al., Nature 428, 831 (2004)]. Thus, finding new approaches to reverse magnetization in a reproducible way, on a time scale shorter than picoseconds, is a fundamental challenge with important consequences for magnetic data storage technology. This thesis demonstrates that the magnetic bit can be switched on a timescale shorter than picosecond by firing a very short pulse of circularly-polarized laser light at it. No external magnetic field was required to flip the bit. This means that that the bit value could be changed ~50.000 times faster than the fastest conventional memory, thus breaking what was previously called the speed limit of magnetic recording.
