Temperature dependence of the high-field magnetization in Fe-Ag granular alloys and discontinuous multilayers

Fe-Ag co-deposited granular alloy and discontinuous multilayer samples with 10-36 at% Fe average compositions were prepared by vacuum evaporation onto Si(111) single crystal substrates at room temperature. The magnetic properties of the samples were studied by SQUID and in-field Moessbauer spectroscopy. Superparamagnetic behaviour was observed for all the samples with blocking temperatures (TB) steeply increasing with increasing Fe concentration. The bulk magnetization (M) measured in 5 T shows linear temperature dependence for both types of samples, and the relative decrease with temperature is much larger for a granular alloy than for a multilayer sample of equal TB. The Moessbauer spectroscopy results indicate that the faster decrease of the high field magnetization in granular alloys is explained by the larger amount of small grains that are not aligned by the 5 T field.