  We study the effects of external magnetic fields on the precision of
parameter estimation with thermal entanglement of two spins in XX model, in the
presence of Dzyaloshinskii-Moriya (DM) interaction. Calculating the quantum
Fisher information, we show that homogeneous magnetic field B, inhomogeneous
magnetic field b or DM interaction D increases the precision of parameter
estimation, overwhelming the destructive effects of thermalization. We also
show that for the model in consideration, the effects of b and D are the same.
However, the existence of both b and B (or both D and B) decreases the
precision. We find that in order to increase the precision in parameter
estimation tasks, applying b in the ferromagnetic case and B in the
antiferromagnetic case should be preferred.
