Exchange scaling of ultrafast angular momentum transfer in 4f antiferromagnets
With use of time-resolved soft x-ray resonant diffraction the ultrafast demagnetization of an antiferromagnetic lanthanide intermetallics has been determined. These results could directly determine the angular momentum transfer between different spin sublattices in the magnetization dynamics of 4f moments. By a systematic comparison of the ultrafast angular momentum transfer rates with ab initio calculations, the rate of this transfer channel is found proportional to the magnitude of the antiferromagnetic indirect Ruderman-Kittel-Kasuya-Yosida (RKKY) exchange interaction. This enables to tune the demagnetization rate of selected sublattices and the transfer rate between them, which opens the possibility to engineer such devices, either shortening or prolonging the short-lived collective spin states.