Entanglement in a quantum mixed-spin chain

The pairwise entanglement between neighboring spins in a general mixed-spin chain with arbitrary spins S and 1/2 is investigated in the thermodynamical limit. The entanglement is witnessed by the magnetic susceptibility which determines a characteristic temperature for an entangled thermal state. The characteristic temperature is nearly proportional to the interaction J and the mixed-spin S. The bound of negativity is obtained on the basis of the magnetic susceptibility. It is found that the macroscopic magnetic properties are affected by the quantum entanglement in the real solids.