Revisiting neutron studies of reentrant spin glasses: the role of small-angle scattering

Abstract

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 Au1−x Fe x and amorphous a-Fe1−x Mn 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.

Probing Short‐Range Correlations in the van der Waals Magnet CrSBr by Small‐Angle Neutron Scattering

“…Here, we employ small-angle neutron scattering (SANS) in order to determine the correlation length of the short-range fluctuations, as well as its temperature dependence. In the context of magnetism, SANS is a technique able to resolve structures on a length scale between a few and a few hundred nanometers, thus being able to resolve magnetic short-range correlations, as already demonstrated, [33][34][35][36] while being insensitive to the long-range ones. [37][38][39][40] Our results show the appearance of short-range correlations below ≈200 K, characterized by correlations lengths up to ≈3 nm at T N , and highlight SANS as a powerful technique for characterizing vdW magnets.…”

Introduction to the special issue on Magnetic small-angle neutron scattering – from nanoscale magnetism to long-range magnetic structures

“…SANS with polarized neutrons is capable of determining the spin-wave stiffness and energy gap of low-energy magnons, even for amorphous ferromagnetic samples. The role of SANS in the investigation of reentrant spin glasses close to a canonical spin glass is discussed and revisited by Mirebeau & Martin (2022), focusing on the prototypical materials Au 1Àx Fe x and amorphous a-Fe 1Àx Mn x .…”