  The composition of gamma-ray burst (GRB) jets remained a mystery until
recently. In practice, we usually characterize the magnetization of the GRB
jets ($\sigma_0$) through the ratio between the Poynting flux and matter
(baryonic) flux. With the increasing value of $\sigma_0$, magnetic energy
gradually takes on a dominant role in the acceleration and energy dissipation
of the jet, causing the proportion of thermal component in the prompt-emission
spectrum of GRBs to gradually decrease or even be completely suppressed. In
this work, we conducted an extensive analysis of the time-resolved spectrum for
all \textit{Fermi} GRBs with known redshift, and we diagnose $\sigma_0$ for
each time bin by contrasting the thermal and nonthermal radiation components.
Our results suggest that most GRB jets should contain a significant magnetic
energy component, likely with magnetization factors $\sigma_{0}\geq 10$. The
value of $\sigma_{0}$ seems vary significantly within the same GRB. Future
studies with more samples, especially those with lower-energy spectral
information coverage, will further verify our results.
