anisotropy, whereas Co chian shows easy-plane anisotropy. Moreover, the in-plane anisotropy energy is close to zero except for V chain.\

This work is supported by the Program for New Century Excellent Talents in University (Grant No. NCET-10-0169), the Scientific Research Fund of Hunan Provincial Education Department (Grant No. 10K065), the National Natural Science Foundation of China (Grant Nos. 10874143,11274262, 11274029), the Hunan Provincial Innovation Foundation for Postgraduate (Grant No. CX2012B273).\

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