  By using Monte Carlo simulation on a ferromagnetic core/antiferromagnetic
shell nanoparticle, we investigate in details the exchange bias of the magnetic
hysteresis as a function of both core radius and shell thickness, at low
temperature. It is found that the exchange bias is very sensitive to the core
radius and a small variation of the radius may lead to a big fluctuation of the
bias. In a general tendency the exchange bias is enhanced by increasing shell
thickness and decreasing core radius. The intrinsic correlation between the
exchange bias and the spin configuration on the core-shell interface is
demonstrated. We further investigate the dependence of the exchange bias on
temperature and random field inside the nanoparticle, indicating a monotonous
decreasing of the bias with the magnitude of random field and temperature,
respectively.
