  We give a near-linear time sampler for the Gibbs distribution of the
ferromagnetic Ising models with edge activities $\boldsymbol{\beta} > 1$ and
external fields $\boldsymbol{\lambda}<1$ (or symmetrically,
$\boldsymbol{\lambda}>1$) on general graphs with bounded or unbounded maximum
degree.
  Our algorithm is based on the field dynamics given in [CFYZ21]. We prove the
correctness and efficiency of our algorithm by establishing spectral
independence of distribution of the random cluster model and the rapid mixing
of Glauber dynamics on the random cluster model in a low-temperature regime,
which may be of independent interest.
