Figure: Watching the ultrafast spin Seebeck effect

Figure: Watching the ultrafast spin Seebeck effect

At time 0 femtoseconds, a bilayer made of a magnetic insulator (with magnetization M) and a nonmagnetic metallic layer is heated by an extremely short ultrafast laser pulse. The resulting transport of spin from the magnet to the metal leads to the emission of a terahertz pulse whose measurement allows the researchers to monitor the dynamics of the excited metal electrons with an extremely fine time resolution of 20 femtoseconds. Their work reveals that the strength of the spin transfer is directly proportional to the number of heated metal electrons, which is maximal at about 100 femtoseconds after laser excitation. After about 1000 femtoseconds, the excited metal electrons have cooled down and transferred their excess energy to the atomic lattice.