In ultrafast demagnetization of ferromagnetic metals after femtosecond laser excitation, a central question is how spin angular momentum can be transferred under the optically excited nonequilibrium conditions. One would expect this to happen on the timescale of spin-lattice relaxation, which has however been found to be on the order of 100 ps for Gd [1], much slower than ultrafast...
Antiferromagnetic (AFM) materials have been predicted to show ultrafast magnetic dynamics since no macroscopic magnetization exists and dynamics might not be restricted by conservation of angular momentum. Out of recent studies investigating ferromagnetic materials like pure 4f elements (Gd,Tb,..) or a combination of 3d and 4f elements with (GdFeCo,..) it turned out that that the fast...
