Resolving weak moments in canted antiferromagnets via time-domain terahertz emission spectroscopy

Canted antiferromagnets host weak net magnetization arising from spin canting while preserving the ultrafast response of antiferromagnetic order. Probing such minute moments—especially in thin films—remains challenging, as conventional magneto-optical and electrical techniques lack sufficient sensitivity. Here, we employ time-domain terahertz emission spectroscopy as a contact-free probe of such weak magnetism. Using epitaxial TmFeO 3 /Pt heterostructures as a model system, the emitted THz signal directly follows the orientation of the canted Fe 3+ moment, allowing real-time tracking of its continuous rotation through the spin reorientation transition. Moreover, the THz hysteresis polarity is reversed compared with conventional ferromagnet/Pt systems, indicating an unconventional interfacial magnetic configuration. Our findings establish THz emission spectroscopy as a powerful tool for resolving ultrafast THz emission response in canted antiferromagnetic thin and ultrathin films.