Magnetic anisotropy in Ce/Fe and Ce/FeCoV multilayers

Abstract

Multilayer samples of Ce/Fe and Ce/FeCoV, fabricated by sputtering and characterized by means of x-ray diffraction and reflectivity, were studied by 57Fe Mössbauer spectroscopy and polarized neutron reflectivity. In the Ce/Fe system a paramagnetic Fe phase is observed at room temperature for Fe thicknesses below 20 Å. This phase is ordered at 4.2 K, and is attributed to amorphous Fe at the interface with Ce. In contrast, the Ce/FeCoV system is ferromagnetic at room temperature for all layer thicknesses studied. From the relative intensity of the Mössbauer lines we show that both systems exhibit a perpendicular magnetic anisotropy for magnetic layers of less than 17 Å thickness, indicating a positive interface anisotropy constant, KS. For a selection of Ce/Fe samples, the reorientation of the magnetic moments in magnetic fields applied normal to the layers enabled the magnetic anisotropy energy Keff of each sample to be evaluated. The trend of the values of Keff gave volume and interface anisotropy constants KV = 1.1 (±1.2)×105 J m-3 and KS = 0.98 (±0.15)×10-3 J m-2 for the Ce/Fe system, where the positive values indicate a preference for an out-of-plane orientation of the magnetization.

Magnetism of uranium/iron multilayers: I. Fabrication and characterization

“…The magnetic phases grown in the fabrication of these U/Fe multilayers show some similarities to and some differences from Fe/rare-earth (RE) multilayers reported in the literature. In evaporated Fe/Gd multilayers [31] a magnetic phase identified as amorphous iron is detected at interfaces whereas in Ce/Fe [30] and in the present U/Fe multilayers this is not present. As noted above, the doublet component observed at room temperature splits into a magnetic sextet at 4.2 K in Ce/Fe systems but remains unsplit at this temperature in U/Fe.…”

“…The spectrum of this sample at 300 K contains the doublet component only and in figure 7(a) it can be seen that the spectrum remains as a doublet and does not show magnetic splitting at 4.2 K. This is not consistent with the intermetallic compound UFe 2 , which orders magnetically at 167 K [28,29] to give a magnetically split spectrum. It is also not consistent with the Ce/Fe multilayer system, in which the room temperature doublet component shows magnetic splitting consistent with impure metallic iron at 4.2 K [30].…”

“…The more recent work of this group, using both resonant x-ray reflectivity and x-ray dichroism techniques [13] has shown that the profile of polarization across the Ce layer may be obtained. In addition, in some samples strong interfacial magnetic anisotropy acts to align the Fe moments normal to the layer plane [14].…”