Spin-glass state of Fe/Cr multilayer structures with ultrathin iron layers

The evolution of the magnetic properties of Fe/Cr superlattices with a decrease in the nominal thickness of the iron layers down to atomic dimensions at which these layers are not continuous has been analyzed. Investigations have been carried out with multilayer samples with Fe-layer thicknesses in a range of 2–6 Å and Cr-layer thicknesses of 10 and 20 Å. It has been found that the system with various Fe-layer thicknesses and at various temperatures exhibits various magnetic phases—superparamagnetic, magnetically ordered, and nonergodic—characterized by the dependence of the magnetization of the sample on its magnetic prehistory. It has been shown that the observed nonergodic phase has the properties of a spin glass. A qualitative phase diagram of the magnetic states of the system has been obtained.