Structural and magnetic properties of UHV-evaporated Fe/Tb multilayers: Effect of the substrate temperature

Two series of (Fe/Tb)(20) multilayers deposited at two temperatures (150 K and 300 K) were investigated at room temperature by x-ray diffraction, conversion electron Mossbauer spectrometry, and magnetic measurements. The Fe layer thickness is varying in a large range (0.9-5.3 nm), while the Th layer thickness is fixed to 1.9 nm. Because of the two different types of amorphous modulated structures obtained at the two deposition temperatures, the crystallization of the Fe layers occurs following two different processes for the two series. Then, when the Fe layers are crystallized, experimental Mossbauer and magnetic results indicate a similar layered structure with the same extension for the Fe-Tb inter-faces at the same Fe thickness. For both series, when the crystallization of the Fe layers occurs, an enhancement of the perpendicular magnetic anisotropy (PMA) produced by a sharpening of the interfaces is evidenced. The strong PMA observed in the thinner (bcc-Fe/Tb) multilayers grown at 300 K comes from the dominant interface anisotropy compared to the volume anisotropy due to the thin bcc-Fe thickness. For (bcc-Fe/Tb) multilayers the variation of the saturation magnetization as a function of the Fe thickness allows us to quantify the different magnetic zones inside the multilayers. The deduced anisotropy constants for the interfaces and the volume are K-S = 2.32 mJ/m(2) and K-upsilon = -1.76x10(6) J/m(3).