Magnetic Properties Of Fe-Ag Multilayers With Varying Layer Thickness And Bilayer Number

Fe-Ag multilayers were prepared by vacuum evaporation in a wide range of Fe and Ag thicknesses (t(Fe), t(Ag)) and bilayer numbers (n), while the magnetic properties as a function of these parameters were measured. Samples with discontinuous Fe layers are superparamagnetic (SPM) and our paper shows that t(Ag) and n affect the superparamagnetic blocking temperature (T-B) not only by affecting the interactions between the Fe grains but also through influencing the growth process of Fe and thereby modifying the magnetic-grain-size distribution. A magnetic "phase diagram" of our Fe-Ag multilayers is constructed in the t(Fe), t(Ag), n parameter space, where the SPM and ferromagnetic behaviors are separated by a mixed zone showing the characteristics of both. The measured trend of the susceptibilities attained at the blocking temperature (T-B), increasing with increasing T-B, was explained by the volume distribution of the magnetic particles, as illustrated by calculations for an ensemble of interaction-free magnetic particles.