Thickness and magnetic field dependence of the ferromagnetism of ultrathin Gd films in Gd/W multilayers

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The magnetization of Gd/W multilayers with a constant W film thickness d W=18 Å prepared by electron-beam evaporation in UHV has been studied by SQUID magnetometry as functions of the Gd layer thickness in the range of 8–85 Å and of the external magnetic field. For the multilayer with 8 Å Gd films, the Curie temperature T c is reduced to 13 K. The thickness dependence of T c follows the finite-size scaling except for the thinnest Gd films of 8 and 11 Å. The magnetization induced by the external field at T c is found to increase with decreasing Gd film thickness. These observations are consistent with a change from three- to quasi-two-dimensional Gd film behavior.