12.11.2004: 
Professor Björgvin Hjörvarsson, Uppsala University, Department of physics, Uppsala, Sweden :
Dimensional games in solid state physics.

Phase transitions are fascinating ingredient in our every day life. Skiing and skating are examples of activities, which rely on a seasonal first order phase transition, namely the freezing of water. Furthermore, we are indirectly reminded of the liquid-gas phase boundary each time we dine. Hence, phase transitions are even important ingredients in our lives.

In this talk I will focus on the influence of extension and interaction on phase transitions and ordering. I will discuss the importance of broken symmetry in the exchange interactions on the dimensionality class of the resulting ordering. The main emphasis will be on studies of magnetic heterostructures, where the interlayer exchange can be altered. I will show how the ratio between the inter- and intra-layer interactions control the dimensionality of the fluctuations, and thereby the dimensionality of the phase transition. The influence of the lateral extension will be addressed and its importance for the phase boundary will be highlighted.