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 (${t}_{\mathrm{Fe}}$, ${t}_{\mathrm{Ag}}$) 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 ${t}_{\mathrm{Ag}}$ and $n$ affect the superparamagnetic blocking temperature (${T}_{\mathrm{B}}$) 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 ${t}_{\mathrm{Fe}}$, ${t}_{\mathrm{Ag}}$, $n$ 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 (${T}_{\mathrm{B}}$), increasing with increasing ${T}_{\mathrm{B}}$, was explained by the volume distribution of the magnetic particles, as illustrated by calculations for an ensemble of interaction-free magnetic particles.