Researchers from the University of Twente have developed new models to describe how fast magnetic bits relax to their ground state. The models are mainly intended for the design of nano-devices and represent a significant improvement on previous models.
The hard disk of a computer stores information in magnetic bits. A fundamental limitation on how fast information can be written is the speed with which the polarity of a magnetic bit can be reversed. Writing new information involves lifting the magnetisation from one of two equivalent ground states to the other - adding energy to the system and removing it again. The faster this removal can take place, the faster the possible write speed. The removal process is called magnetisation damping.
Parameter not constant
Up until now scientists predicted how fast a bit returns to its ground state with the help of a constant parameter α. For small structures, however, this Gilbert damping parameter proved not to be constant at all. That is because the magnetisation dampens faster where there are interfaces present.
Scientists at the University of Twente managed to calculate the damping at interfaces between permalloy, an important magnetic alloy, and various non-magnetic materials. They did this with the help of scattering matrices that were calculated fully 'ab-initio' i.e. making only use of the fundamental physical constants.
Thanks to the research at the University of Twente, scientists can now more accurately predict how fast magnetisation reversal occurs for small structures. This is good news for researchers who design new nano-devices and want to be able to predict their behaviour.