Comparison of the magnetar parameters among GRBs (assuming η_x = 0.5), SLSNe, and FRBs. The populations of GRBs and SLSNe can be roughly separated by the line B_p = 10^14.5 G. The blue rectangles mark the inferred magnetar parameter regions for three FRBs (FRB 20121102A (middle), FRB 20190520B (right), and FRB 20240114A (left)). The polar magnetic field B_p shown here is approximated by roughly taking one-tenth of the internal magnetic field B_int obtained from modeling the spectra and light curves of the persistent radio sources (i.e., B_p ∼ B_int/10; Zhao et al. 2026, in preparation). The initial spin period, which lacks direct observational constraints, is assumed to be uniformly distributed between 1 and 10 ms. The magnetic field strengths of these FRB sources are notably similar to those of the GRB sample, suggesting that both populations may be powered by a similar type of strongly magnetized magnetar engine.