Magnetic states of multilayer Fe ∕ Cr structures with ultrathin iron layers

The evolution of the magnetic properties of Fe ∕ Cr superlattices is studied as the nominal thickness of the iron layers is reduced to atomic values, when these layers are no longer continuous. The studies were done on multilayer samples with Fe thicknesses of 2 – 6 Å and chromium spacer thicknesses of 10 and 20 Å . The samples were prepared by molecular beam epitaxy. The static magnetization and complex magnetic susceptibility were measured and FMR spectra taken. It was found that, depending on the thickness of the Fe layers and temperature, different magnetic phases are realized in the system: supermagnetism, magnetic ordering, and a nonergodic state characterized by a dependence of the magnetization of a sample on its magnetic prehistory. The observed nonergodic phase is found to exhibit spin glass properties. A qualitative phase diagram of the magnetic states of this system is constructed.