Figure 3a shows magnetization curves for 60-repeat (Fe40Å/Si14Å) multilayers grown simultaneously on glass and MgO(001). The saturation fields H s appear to be similar for the two films. On the other hand, the remanent magnetization is 58% for the film on glass and 7% for the film grown on MgO. A remanence as low as 1% has been observed for other multilayers grown on MgO substrates. SQUID magnetometer data taken up to higher fields gives a saturation field of 9.75 kOe for the multilayer on MgO at room temperature. Assuming for a moment that the interlayer coupling is purely bilinear in nature, a well-known formula relates the saturation field to the AF coupling strength: A12 = Hs MS tFe / 4 where M S is the saturation magnetization and t Fe is the thickness of an individual Fe layer.[8] Use of this equation with H S = 9.75 kOe and the measured magnetization MS = 1271 emu/cm3 gives A 12 = 1.2 erg/cm2. This AF coupling value is comparable in size to the coupling measured in metal/metal multilayers multilayers[9].
Figure 3b shows magnetization curves for Fe100Å/Si14Å/Fe100Å trilayer films grown on Al2O3 (1120), Ge(001), and MgO(001) substrates. All three of the magnetization curves in Fig. 3b were taken with the field applied along an Fe(100) easy direction. Significant in-plane anisotropy of the magnetization curves occurs for the films on the Ge and MgO substrates, similar to what has been observed for Fe/Cr/Fe trilayers.[8] The observation of magnetocrystalline anisotropy in the film on MgO but not in the film grown on Al2O3 is consistent with expectations from the ø scans, which show that the in-plane orientation of the film on MgO is much stronger.
Figure 3b once again demonstrates that the degree of remanence in Fe/Si multilayers is strongly related to the quality of layering. While the remanent magnetization of the epitaxial trilayers on Ge and MgO is only about 5% of the saturated value, the remanence of the polycrystalline trilayer on Al2O3 is close to 50%. The remanent magnetization of the trilayers on Ge and MgO is about 5% in the in-plane hard direction (H || Fe(110)) as well.
A SQUID magnetometer has been used to measure the magnetization curves of the IBS-grown Fe/Si multilayers at lower temperatures.[10] The temperature dependence of the remanent magnetization of these films is similar to that reported by other authors.[3]