Zhang W Maldonado P Jin Z Seifert TS Arabski J Schmerber G Beaurepaire E Bonn M Kampfrath T Oppeneer PM Turchinovich D 2020 A material's magnetic state and its dynamics are of great fundamental research interest and are also at the core of a wide plethora of modern technologies. However, reliable access to magnetization dynamics in materials and devices on the technologically relevant ultrafast timescale, and under realistic device-operation conditions, remains a challenge. Here, we demonstrate a method of ultrafast terahertz (THz) magnetometry, which gives direct access to the (sub-)picosecond magnetization dynamics even in encapsulated materials or devices in a contact-free fashion, in a fully calibrated manner, and under ambient conditions. As a showcase for this powerful method, we measure the ultrafast magnetization dynamics in a laser-excited encapsulated iron film. Our measurements reveal and disentangle distinct contributions originating from (i) incoherent hot-magnon-driven magnetization quenching and (ii) coherent acoustically-driven modulation of the exchange interaction in iron, paving the way to technologies utilizing ultrafast heat-free control of magnetism. High sensitivity and relative ease of experimental arrangement highlight the promise of ultrafast THz magnetometry for both fundamental studies and the technological applications of magnetism. application/pdf https://sonar.ch/global/documents/98835 eng info:eu-repo/semantics/altIdentifier/doi/10.1038/s41467-020-17935-6 info:eu-repo/semantics/altIdentifier/pmid/32843645 info:eu-repo/semantics/openAccess Nature communications. - 2020 General Biochemistry, Genetics and Molecular Biology General Physics and Astronomy General Chemistry Ultrafast terahertz magnetometry. http://purl.org/coar/resource_type/c_6501