20. Spin and Ferroic Glasses

Spin glasses are a broad class of magnetic materials that exhibit varying degrees of disorder and magnetic frustration, resulting in characteristic glassy relaxation behavior including frequency-dependent susceptibility, aging, and memory. Ferroic glasses include spin glasses and also relaxor ferroelectrics and strain glasses, which exhibit glassy dynamics in polarization and strain respectively, in similar ways to spin glasses. This chapter introduces ferroic and spin glasses, their phenomenological classification, and some parallels with structural (amorphous) glasses. A brief theoretical treatment is given, including modeling of the relaxation phenomena in ferroic glasses. Strain glasses and relaxors are discussed, followed by a detailed taxonomy of spin glasses and comparison with collectively behaving particle systems and structurally amorphous magnetic materials. Finally, some characteristic experimental methods are discussed, and an outlook for the future involvement of glass scientists in the study of spin glasses is offered.