The application is discussed of neutron methods to the study of reentrant spin glasses (RSGs), close to the transition towards a `canonical' spin glass (SG). The focus is on two emblematic systems, namely Au_1−xFe_x and amorphous a-Fe_1−xMn_x. A set of experimental results is presented to highlight their peculiar static and dynamic properties. The role of small-angle neutron scattering (SANS) is stressed as an important tool to unravel the structure of these complex systems over mesoscopic length scales. Finally, recent SANS results performed under an applied magnetic field in the region of the RSG → SG transition are presented. They show that vortex-like defects are present in the RSG region up to the critical line and vanish in the SG region. These defects, which develop only in a ferromagnetic medium, could be a key feature to probe the emergence of long-range magnetic order.

中文翻译：

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重入自旋玻璃的中子研究：小角散射的作用

讨论了中子方法在研究重入自旋玻璃 (RSG) 中的应用，接近向“规范”自旋玻璃 (SG) 的过渡。重点是两个标志性系统，即 Au _{1− x} Fe _x和无定形 a-Fe _{1− x} Mn _x. 提出了一组实验结果，以突出它们独特的静态和动态特性。强调小角中子散射 (SANS) 的作用是在介观长度尺度上解开这些复杂系统结构的重要工具。最后，介绍了在 RSG → SG 过渡区域的外加磁场下执行的最新 SANS 结果。他们表明，涡流状缺陷存在于 RSG 区域直至临界线，并在 SG 区域消失。这些仅在铁磁介质中发展的缺陷可能是探测长程磁序出现的关键特征。