Modifying Critical Exponents of Magnetic Phase Transitions via Nanoscale Materials Design.

We demonstrate a nanoscale materials design path that allows us to bypass universality in thin ferromagnetic films and enables us to tune the critical exponents of ferromagnetic phase transitions in a very wide parameter range, while at the same time preserving scaling in an extended phase space near the Curie temperature. Our detailed magnetometry results reveal that single crystal CoRu alloy films, in which the predefined depth dependent exchange coupling strength follows a V-shaped profile, exhibit critical scaling behavior over many orders of magnitude. Their critical exponents, however, can be designed and controlled by modifying their specific nanoscale structures, thus demonstrating full tunability of critical behavior.