  We investigate the entanglement arising naturally in a 1D Ising chain in a
magnetic field in an arbitrary direction. We find that for different
temperatures, different orientations of the magnetic field give maximum
entanglement. In the high temperature limit, this optimal orientation
corresponds to the magnetic field being perpendicular to the Ising orientation
(z direction). In the low temperature limit, we find that varying the angle of
the magnetic field very slightly from the z direction leads to a rapid rise in
entanglement. We also find that the orientation of the magnetic field for
maximum entanglement varies with the field amplitude. Furthermore, we have
derived a simple rule for the mixing of concurrences (a measure of
entanglement) due to mixing of pure states satisfying certain conditions.
