Principles of nuclear magnetic ordering
Principles of nuclear magnetic ordering
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核磁有序原理
DOI：
10.1103/physrevb.10.226
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发表时间：
1974
影响因子：
3.7
通讯作者：
A. Abragam
中科院分区：
文献类型：
--
作者：
M. Goldman;M. Chapellier;Vu Hoang Chau;A. Abragam
我们在本文中描述了在偶极子-偶极子相互作用的核自旋系统中产生和观察磁序的原理。产生有序化所需的冷却（仅涉及原子核）是通过两步过程获得的：高场中的动态极化，然后是绝热核退磁。该研究主要限于旋转框架中的绝热退磁，其中有效的核自旋-自旋相互作用是截断偶极相互作用。我们简要列出了一些可以进行的测量，主要与磁共振技术相关，以及它们在订购时产生的信息。通过使用局部韦斯场近似来预测正温度和负温度下有序结构的性质。在自旋为 1/2 的简单立方系统的情况下，人们预测会出现三种不同的反铁磁结构。韦斯场近似，偶尔辅以自旋温度理论的高温近似，最终用于预测反铁磁态的熵的各种特性：亚晶格磁化强度、跃迁熵、横向和纵向磁化率、跃迁场以及快通道色散信号的形状。
We describe in this article the principles of production and observation of magnetic ordering in systems of nuclear spins subjected to dipole-dipole interactions. The cooling necessary for producing ordering, which concerns only the nuclei, is obtained by a two-step process: dynamic polarization in a high field followed by adiabatic nuclear demagnetization. The study is mostly limited to adiabatic demagnetization in the rotating frame, for which the effective nuclear spin-spin interactions are truncated dipolar interactions. We list briefly a number of measurements that can be made, mostly relevant to magnetic resonance techniques, together with the information they yield on the ordering. The prediction of the nature of ordered structures, both at positive and negative temperatures, is made through the use of the local Weiss-field approximation. In the case of simple cubic systems of spins 1/2, one predicts the occurrence of three different antiferromagnetic structures. The Weiss-field approximation, occasionally supplemented with high-temperature approximation to spin temperature theory, is finally used for predicting as a function of entropy various properties of the antiferromagnetic states: sublattice magnetizations, transition entropy, transverse and longitudinal susceptibilities, transition field, and shape of the fast-passage dispersion signal.