In this thesis, the essential concepts of entanglement and some of its criterion have been discussed. Then introducing thermal entanglement in spin chain, thermal entanglement in Ising, and in star and ring-star structure have been studied.
A summary of result follows:
1- In all structure discussed in this thesis, increasing tempradure cause to decrease entanglement gradually.
2- In star structure, in and model by increasing coupling coefficient entanglement increased. Also, by comparison between and model, we found that anistropic in XYZ cause to in specific value of magnetic fields entanglement becomes zero and suddenly increased.
3- In Ising ring-star structure, by increasing frustration parameter entanglement in star part decreased and in ring part increased. But in model by increasing frustration parameter, entanglement in two parts decreased.