The ultimate speed limit of the control of spins in a solid-state magnetic material has been determined. The results pave the way to the unprecedented frequency range of 20 THz for magnetic recording devices, which can be employed also at the nanometer scale. The practical implementation of schemes of magnetic control, based on the use of electric currents, has historically been hampered by significant heating, which requires cooling systems. Artistic representation of coherent control of femtosecond nanomagnons. Courtesy of Radboud University. Instead, researchers from Radboud University and the University Politecnico di Milano, Italy, used an approach that relied on the magnetic moment of electrons (that is, the spin) rather than the charge. The phenomenon has recently turned into two major research fields: spintronics and magnonics. The team followed in real time the ultrafast dynamics of the macroscale magnetic order parameter in the Heisenberg antiferromagnet KNiF3, triggered by the impulsive optical generation of spin excitations with the shortest possible nanometer wavelength and femtosecond period. Magneto-optical pump-probe experiments also demonstrated the coherent manipulation of the phase and amplitude of the femtosecond nanomagnons, whose frequencies were defined by the exchange energy. The researchers said the findings open up opportunities for fundamental research on the role of short-wavelength spin excitations in magnetism and strongly correlated materials. They also suggest that nanospintronics and nanomagnonics can employ coherently controllable spin waves with frequencies in the 20 THz domain. The research was published in Nature Communications (doi: 10.1038/ncomms10645).