New ferromagnetic superconductor—CsEuFe4As4
Superconductivity (SC) and ferromagnetism (FM) are mutually antagonistic collective phenomena in solids. Macroscopically, a superconductor expels magnetic fluxes from its interior below the superconducting critical temperature TSC. By contrast, a ferromagnet magnetizes itself (for a single magnetic domain) spontaneously below the ferromagnetic transition temperature TFM. Although SC and FM are incompatible in most cases, there is still the possibility of their coexistence, which, since the 1950s, has become a long-standing issue for scientists who work in the field of superconductivity. Since the late 1970s, a few material systems called "magnetic superconductors" have been considered as the candidates of ferromagnetic superconductors (FMSC). However, bulk SC and full FM were rarely observed simultaneously.