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arXiv 0904.4790cond-mat.str-elcond-mat.mtrl-sci
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双交换模型中Jahn-Teller耦合对居里温度的影响

Effect of Jahn-Teller coupling on Curie temperature in the Double Exchange Model

Vasil Michev, Naoum Karchev

摘要:

我们考虑了具有Jahn-Teller(JT)耦合的锰氧化物的双带双交换模型,并探讨了由于JT畸变而导致的铁磁性的抑制。用Schwinger玻色子表示$\emph{t}_{2g}$电子的局域自旋,并引入两个自旋单态费米子算符代替$e_{g}$电子算符.在新的费米场中,在位Hund相互作用是对角形式的,并且可以精确地解释它。我们将自旋单重态费米子积分出来,导出了一个描述总磁化强度局域取向的有效矢量海森堡模型。交换常数随空间方向的不同而不同,并取决于$\emph{e}_{g}$电子的密度$n$和JT能量。在零温下,随着$\emph{e}_{g}$电子密度的增加,体系经历了从铁磁相$(0<n<n_c)$到A型反铁磁相$(n_c<n)$的相变。临界值$n_c$随着JT能量的增加而减小。在有限温度下,我们计算了不同JT能量下居里温度随电子密度的变化。结果表明,JT耦合强烈地抑制了自旋涨落,降低了居里温度。

英文摘要:

We consider the two-band double exchange model for manganites with Jahn-Teller (JT) coupling and explore the suppression of the ferromagnetism because of the JT distortion. The localized spins of the $\emph{t}_{2g}$ electrons are represented in terms of the Schwinger bosons, and two spin-singlet Fermion operators are introduced instead of the $e_{g}$ electrons' operators. In terms of the new Fermi fields the on-site Hund's interaction is in a diagonal form and one accounts for it exactly. Integrating out the spin-singlet fermions, we derive an effective Heisenberg model for a vector which describes the local orientations of the total magnetization. The exchange constants are different for different space directions and depend on the density $n$ of $\emph{e}_{g}$ electrons and JT energy. At zero temperature, with increasing the density of the $\emph{e}_{g}$ electrons the system undergoes phase transition from ferromagnetic phase $(0<n<n_c)$ to A-type antiferromagnetic phase $(n_c<n)$. The critical value $n_c$ decreases as JT energy is increased. At finite temperature we calculate the Curie temperature as a function of electron density for different JT energy. The results show that JT coupling strongly suppresses the spin fluctuations and decreases the Curie temperature.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

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