  The discovery of atomic monolayer magnetic materials has stimulated intense
research activities in the two-dimensional (2D) van der Waals (vdW) materials
community. The field is growing rapidly and there has been a large class of 2D
vdW magnetic compounds with unique properties, which provides an ideal platform
to study magnetism in the atomically thin limit. In parallel, based on
tunneling magnetoresistance and magneto-optical effect in 2D vdW magnets and
their heterostructures, emerging concepts of spintronic and optoelectronic
applications such as spin tunnel field-effect transistors and spin-filtering
devices are explored. While the magnetic ground state has been extensively
investigated, reliable characterization and control of spin dynamics play a
crucial role in designing ultrafast spintronic devices. Ferromagnetic resonance
(FMR) allows direct measurements of magnetic excitations, which provides
insight into the key parameters of magnetic properties such as exchange
interaction, magnetic anisotropy, gyromagnetic ratio, spin-orbit coupling,
damping rate, and domain structure. In this review article, we present an
overview of the essential progress in probing spin dynamics of 2D vdW magnets
using FMR techniques. Given the dynamic nature of this field, we focus mainly
on broadband FMR, optical FMR, and spin-torque FMR, and their applications in
studying prototypical 2D vdW magnets. We conclude with the recent advances in
laboratory- and synchrotron-based FMR techniques and their opportunities to
broaden the horizon of research pathways into atomically thin magnets.
