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    文林, 胡爱元

    Effect of biquadratic exchange and anisotropy on the critical temperature of antiferromagnet

    Wen Lin, Hu Ai-Yuan
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    • 本文基于双时格林函数方法, 通过对不同格点和同格点的高阶格林函数分别采用Tyablikov和Callen退耦近似, 系统研究了双二次型交换作用和各向异性对简单立方晶格反铁磁模型相变的影响. 得到了相变温度的解析表达式, 发现相变温度随着各向异性的增强而升高, 但随着双二次型相互作用的增强而下降.
      The existence of biquadratic exchange had been well established by Anderson, Huang and Allen. Early investigations indicated that the biquadratic exchange term in spin Hamiltonian was found to have significant effects on the magnetic properties of compounds containing iron-group ions or rare-earth metal ions. Recently, studying the anisotropic magnetic excitation of iron-based superconducting materials indicated that the experimental phenomenon cannot be explained well only by a simple collinear Heisenberg antiferromagnetic model. However, if the nearest neighbor biquadratic spin coupling is introduced, the experiment can be well explained. Similar results had also been obtained in the investigation of the superconducting material FeSe. As a result, exploring the effect of biquadratic exchange interactions on the magnetic properties of magnetic systems is significance. In this paper, we use the double-time Green's function method to study the properties of the spin-1 Heisenberg antiferromagnets with biquadratic exchange interactions and anisotropy on a three-dimensional lattice. We derive the equation of motion of the Green's function by a standard procedure. In the course of this, the higher order Green functions have to be decoupled. For the higher order Green functions of different lattice points, a Tyablikov or random phase approximation decoupling are used to decuple. For the higher order Green functions of the same lattice points, we adopt the Anderson-Callen decoupling to decouple. Based on the above procedures, the analytic expressions of the magnetization and critical temperature are obtained. The effects of biquadratic exchange interactions and anisotropy on the critical temperature are discussed in detailed. Our results show that the critical temperature increases with the increase of the anisotropy for a given biquadratic interaction. Regardless of the value of the anisotropy, the critical temperature always decreases with the increase of the biquadratic interaction. As the value of anisotropic parameter $\eta = 0$ , there is an obvious linear relationship between the critical temperature and the biquadratic interaction. However, when the anisotropy of the system becomes weaker, there is no such linear relationship between them. By comparing similar ferromagnetic models, it is found that the results of this paper are significantly different from those of the ferromagnetic model. When the biquadratic interaction is equal to 0, our results agree with other theoretical results.
          通信作者:胡爱元,huaiyuanhuyuanai@126.com
        • 基金项目:国家自然科学基金(批准号: 11875010)和重庆市自然科学基金(批准号: cstc2019jcyj-msxmX0217, cstc2019jcyj-msxmX0251)资助的课题
          Corresponding author:Hu Ai-Yuan,huaiyuanhuyuanai@126.com
        • Funds:Project supported by the National Natural Science Foundation of China (Grant No. 11875010), and the Chongqing Natural Science Foundation (Grant Nos. cstc2019jcyj-msxmX0217, cstc2019jcyj-msxmX0251)
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      • PDF下载量:96
      • 被引次数:0
      出版历程
      • 收稿日期:2020-01-12
      • 修回日期:2020-03-24
      • 刊出日期:2020-05-20

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