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摘要翻译：
在前人的工作中，我们提出了一个计算局域磁矩晶体相变的模型，该模型在低温下具有“圆锥形”排列，在变得完全无序之前，它在更高的温度下转变为更对称的结构（取决于化合物）。该模型假设磁矩之间的相互作用为双线性和双二次直到五次邻域，对于任意给定的T，通过平均场近似(MFA)得到自由能最小的结构。相互作用常数由从头算能量计算得到。在本工作中，我们对该模型进行了改进，修正了MFA，使系统具有连续（而不是不连续）的激发态谱。在前人对LaMn_2Ge_2和LaMn_2Si_2的研究中，我们发现随着T的增加，可以得到不同结构的跃迁，这与实验有很好的定性一致性。然而，临界温度过高。用新的MFA我们得到了基本相同的相变行为，临界温度更接近实验值。
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英文标题：
《Transitions involving conical magnetic phases in a model with bilinear
and biquadratic interactions》
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作者：
Vittorio Massidda
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最新提交年份：
2007
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分类信息：
一级分类：Physics 物理学
二级分类：Statistical Mechanics 统计力学
分类描述：Phase transitions, thermodynamics, field theory, non-equilibrium phenomena, renormalization group and scaling, integrable models, turbulence
相变，热力学，场论，非平衡现象，重整化群和标度，可积模型，湍流
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英文摘要：
In a previous work a model was proposed for the phase transitions of crystals with localized magnetic moments which at low temperature have a "conical" arrangement that at higher T transforms into a more symmetrical structure (depending on the compound) before becoming totally disordered. The model assumes bilinear and biquadratic interactions between magnetic moments up to the fifth neighbours, and for any given T the structure with the least free energy is obtained by a mean-field approximation (MFA). The interaction constants are derived from ab initio energy calculations. In this work we improve upon that model modifying the MFA in such a way that a continuous (instead of discontinuous) spectrum of excited states is available to the system. In the previous work, which dealt with LaMn_2Ge_2 and LaMn_2Si_2, we found that transitions to different structures can be obtained for increasing T, in good qualitative agreement with experiment. The critical temperatures, however, were exaggerately high. With the new MFA we obtain essentially the same behaviour concerning the phase transitions, and critical temperatures much closer to the experimental ones.
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PDF链接：
https://arxiv.org/pdf/708.3345
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