Research: Magnetic Phase Transitions Become Faster
The Uppsala researcher Peter Oppeneer at the department of physics and astronomy has together with researchers from the University of Colorado Boulder, USA, shown on a faster magnetic phase transition than what one previously has been able to observe.
A magnetic phase transition means that the magnetic order in a material is transformed and for example goes from an ordered magnetic to a non-magnetic state when the temperature is slowly changed and the entire material adapts to the new temperature.
How fast a magnetic phase transition may take place is still unknown, but the results from the study which were published in the reputed Science Advances Mars 2, 2018 shows on the fastest magnetic phase transition that one has been able to observe to this date.
What the researchers have arrived at in the study is that the phase transition from a magnetic to a non-magnetic state in nickel is possible within 20 femtoseconds (10-15 s) without all the constituents of the material, such as the electron, the atom and the magnetic moment, having the same temperature.
The researchers made use of ultrashort pulses of light for time resolved measurements with two spectroscopy methods; photoemission spectroscopy to measure the state of the electron and magnetooptic spectroscopy to measure the magnetic state in nickel. Together the two spectroscopy methods gave a complete picture of the changes in the structure of the electron and in the magnetic moment showing that the same critical values in the heat capacity of the material which describes the material's behaviour in thermic equilibrium surprisingly also holds true when the material is far from equilibrium.
This research is pure basic research but the discovery may make way for new, faster ways to switch magnetic phases which may lead to faster optical elements in the future.
P. Tengdin et al., Critical behavior within 20 fs drives the out-of-equilibrium laser-induced magnetic phase transition in nickel, Science Advances 4, eaap9744 (2018)