  THz magnetization dynamics is a key property of antiferromagnets as well as
ferrimagnets that could harness the THz forefront and spintronics. While most
of the present THz measurement techniques are for bulk materials whose
sensitivities rely on the volume of the material, measurement techniques
suitable for thin films are quite limited. In this study, we explored and
demonstrated electrical detection of the antiferromagnetic dynamics in
ferrimagnetic Gd-Co thin films by using a 154 GHz gyrotron, a high-power
electromagnetic wave source. Captured resonant modes allow us to characterize
the peculiar magnetization dynamics of the Gd-Co around the net angular
momentum compensation. As the gyrotron frequency is scalable up to THz, our
demonstration can be an important milestone toward the THz measurements for
antiferro- and ferri- magnetic thin films.
