Phase diagrams and multicritical points in randomly mixed magnets. II. Ferromagnet-antiferromagnet alloys.
Phase diagrams and multicritical points in randomly mixed magnets. II. Ferromagnet-antiferromagnet alloys.
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随机混合磁体中的相图和多临界点。
DOI：
10.1103/physrevb.19.3776
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发表时间：
1979
期刊：
影响因子：
--
通讯作者：
A. Aharony
中科院分区：
文献类型：
--
作者：
S. Fishman;A. Aharony
在平均场近似下，用重整化群方法研究了铁磁体和反铁磁体（或两个不同周期的反铁磁体）的淬火无序合金的相图和临界行为。反铁磁序参量被转化为铁磁序参量的组合，以研究铁磁和反铁磁序同时成为临界序的可能性。对随机变量求平均得到一个不变的有效哈密顿量，其中m分量序参数被替换为nm分量序参数，并且在计算结束时取极限n→ 0。在平均场近似下得到了浓度-温度平面上的相图，并讨论了有序相的性质。除了纯组分的有序相外，有时还发现混合相，当m> 1时，在该相中，铁磁序参量矢量和反铁磁序参量矢量相互垂直。重整化群被用来研究所有这些有序相相遇的多临界点。我们找不到一个稳定的不动点来描述这个多临界点。这一事实的物理影响进行了讨论。最后，对随机合金的实验进行了回顾，并提出了有待进一步研究的问题。
The phase diagrams and critical behavior of a quenched random alloy of a ferromagnet and an antiferromagnet (or of two antiferromagnets with different periodicities) are studied in the mean-field approximation and by renormalization-group techniques. The antiferromagnetic order parameters are transformed into combinations of ferromagnetic order parameters, in order to study the possibility that ferromagnetic and antiferromagnetic orderings will become critical simultaneously. Averaging over the random variables yields a translationally invariant effective Hamiltonian, in which the m-component order parameters are replaced by nm-component order parameters and the limit n→ 0 is taken in the end of the calculation. The phase diagram in the concentration-temperature plane is obtained in the mean-field approximation, and the nature of the ordered phases is discussed. In addition to the ordered phases of the pure ingredients, a mixed phase is sometimes found. For m> 1, the ferromagnetic-and antiferromagnetic-order-parameter vectors are perpendicular to each other in this phase. The renormalization group is applied to study the multicritical point at which all these ordered phases meet. We don't find a stable fixed point appropriate for the description of this multicritical point. The physical implications of this fact are discussed. Finally, experiments on random alloys are reviewed and problems that should be studied experimentally are raised.