Fluctuation effects on the quadrupolar ordering in magnetic field
Fluctuation effects on the quadrupolar ordering in magnetic field
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磁场涨落对四极有序的影响
DOI：
10.1143/jpsj.67.2460
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发表时间：
1997
影响因子：
1.7
通讯作者：
Y. Kuramoto
中科院分区：
文献类型：
--
作者：
N. Fukushima;Y. Kuramoto
考虑到序参量的涨落，研究了磁场对四极有序的影响。对于最近邻四极相互作用的最简单模型，利用最近提出的有效介质理论导出了相变温度和比热。结果表明，磁场H对四极有序有两种相互竞争的作用，一种是通过抑制有序参数各分量之间的涨落来促进有序化，另一种是阻碍有序化，如反铁磁体.发现前者为H2阶，后者为H4阶。因此，在弱磁场下，涨落被抑制，相变温度随磁场的增加而升高。涨落效应是如此之强，以至于即使没有近藤效应，四极序下释放的熵也只有全值ln 4的四分之一左右。
Effects of magnetic field on the quadrupolar ordering are investigated with inclusion of fluctuation of order parameters. For the simplest model with the nearest-neighbor quadrupolar interaction, the transition temperature and the specific heat are derived by the use of the recently proposed effective medium theory. It is shown that magnetic field H has two competing effects on the quadrupolar ordering; one is to encourage the ordering by suppressing the fluctuation among different components of order parameters, and the other is to block the ordering as in antiferromagnets. The former is found to be of order H 2 and the latter of order H 4 . Hence the fluctuation is suppressed for weak fields, and the transition temperature increases with magnetic field. The fluctuation effect is so strong that the entropy released at the quadrupolar ordering is only about a quarter of the full value ln 4 even without the Kondo effect.