The origin of magnetism in crystals and the techniques for characterizing magnetic structures: From microscopic ions to macroscopic magnetic expressions

Investigating the magnetic structure of crystals is a crucial area of research in magnetic materials. Different crystals exhibit magnetic features related to their ionic composition and crystal structure. Manipulating the magnetic properties of materials requires a better understanding of the mechanisms regulating the magnetic properties and the magnetic structure of crystals. Currently, characterization techniques with high spatial resolution and spin sensitivity are the main tools to study the magnetic structure of materials. Meanwhile, the high-speed development of magnetic simulation and computation techniques has minimized the experimental cost, predicted the basic information about the magnetic structure of crystals, and verified the accuracy of the characterization techniques. This review first looks at the origin of crystal magnetism. It analyses the mechanisms regulating crystal magnetism in different perspectives (from single ions to macroscopic magnetic expressions), and then summarizes the main methods used to characterize the magnetic structure, outlining the specifics of the various techniques in the existing studies, which have used either a single magnetic characterization technique or a combination of techniques to study the magnetic structure of crystals in all scales. Finally, it discusses how magnetic characterization techniques and computational simulations can be better applied to the analysis of the magnetic structure of crystals, which has important applications for establishing crystallographic laws for magnetic materials.