Experimental study of the structural and magnetic properties of Fe/Tb multilayers

Sputtered Fe/Tb multilayers of various Fe and Tb thicknesses (0.22 less than or equal to t(Fe) less than or equal to 3.3 nm, 0.2 less than or equal to t(Tb) less than or equal to 1.9 nm) have been investigated by x-ray diffraction, Mossbauer spectrometry, and magnetic measurements in the 4.2-300 K temperature range. A compositionally modulated structure is shown with the appearance of pure-amorphous iron in the center of the Fe layers thicker than 1.2 nm. When the Fe layers are thick enough (greater than or equal to 2.2-2.4 nm), the Fe layers will crystallize. The magnetic properties (M, T-comp, T-c,...) were analyzed in relation with Fe and Tb thicknesses and also with mean Tb composition. In agreement with the structure, the departure of magnetic properties from those of the corresponding amorphous alloys is observed when pure amorphous iron appears in the center of the layers. The dependence of the magnetic anisotropy axis on temperature and thicknesses is interpreted taking into account the composition modulation in the multilayers and the dominant magnetic subnetwork.