  We in this paper study quantum correlations for two neutral spin-particles
coupled with a single-mode optical cavity through the usual magnetic
interaction. Two-spin entangled states for both antiparallel and parallel
spin-polarizations are generated under the photon coherent-state assumption.
Based on the quantum master equation we derive the time-dependent quantum
correlation of Clauser-Horne-Shimony-Holt (CHSH) type explicitly in comparison
with the well known entanglement-measure concurrence. In the two-spin singlet
state, which is recognized as one eigenstate of the system, the CHSH
correlation and concurrence remain in their maximum values invariant with time
and independent of the average photon-numbers either. The correlation varies
periodically with time in the general entangled-states for the low average
photon-numbers. When the photon number increases to a certain value the
oscillation becomes random and the correlations are suppressed below the Bell
bound indicating the decoherence of the entangled states. In the high
photon-number limit the coherence revivals periodically such that the CHSH
correlation approaches the upper bound value at particular time points
associated with the cavity-field period
