  Polymers are among the most important materials in the modern society being
found almost in every activity of our daily life. Understanding their chemical
and physical properties lead to improvements of their usage. The correlation
functions are one of most important quantities to understand a physical system.
The characteristic way it behaves describe how the system fluctuates, and much
of the progress achieved to understand complex systems has been due to their
study. Of particular interest in polymer science are the space correlations
which describe its mechanical behavior. In this work I study the stiffness of a
polymer immersed in a magnetic medium and trapped in an optical tweezers. Using
Monte Carlo simulations the correlation function along the chain and the force
in the tweezers are obtained as a function of temperature and density of
magnetic particles. The results show that the correlation decay has two
regimes: an initial very fast decay of order the monomer-monomer spacing and a
power law in the long distance regime. The power law exponent has a minimum at
a temperature $T_{min}$ for any non zero density of magnetic particles
indicating that the system is more correlated in this region. Using a formula
for the persistence length derived from the WLC theory one observed that it has
a maximum at the same temperature. These results suggest that the correlations
in the system may be a combination of exponential and power law.
