Magnetization and FMR studies of [Fe/Cr]_n structures with ultrathin iron layers

Abstract

Magnetic multilayer structures [Fe(tFe)/Cr(tCr)]n with ultrathin (tFe<5Å) iron layers prepared by a molecular beam epitaxy were studied using SQUID-magnetometry and ferromagnetic resonance technique. For the samples with t Fe 3Å, the obtained magnetization curves and resonance spectra are typical for regular magnetic superlattices. On the contrary, the samples with tFe 3Å demonstrate superparamagnetic-like behavior. These samples show a strong temperature dependence of their static and resonance magnetic properties. To explain the obtained results, we propose a theoretical model considering a cluster structure of thin iron layers. Magnetization curves and resonance spectra are calculated using an effective field approximation taking into account an interlayer interaction and cluster size distribution. The calculated dependencies show a qualitative agreement with the experimental data.