X-ray diffractometry at grazing incidence has been performed upon Nin/Fen multilayers with 6<2n<30mpl (n = no. of monolayers per nn layer, mpl), as a further test that the observed reduction in magnetisation (as n decreases) was not due to interfacial alloying. The results show that the interfaces are terraced to the extent that pinholes occur in the thinner layers. The layers became continuous for modulations 2n>10mpl. Each X-ray scan revealed a series of peaks which corresponded to integer monolayer differences in modulation periodicity. In contrast, interfacial alloying would have produced a broad single peak.
M-H loops were performed on the samples for the range of temperatures 6<T<300K using a vibrating sample magnetometer with the field always applied in the plane of the sample. The sample coercivity was observed to vary with modulation wavelength such that at a modulation of 2n=16mpl it was about a factor of three greater than at either 2n=6mpl or 2n=30mpl. The coercivity peak occurs at a value of n equal to the critical layer thickness for the transformation of the Fe from FCC to BCC. High angle X-ray diffractometry shows an apparent change in planar spacing at the same modulation layer thickness (n=8mpl).
The ratio of remnant magnetisation at low temperature to that at room temperature, RT, was greater than unity for all the samples measured. The ratio increased as the modulation period of the samples decreased. This is consistent with a modulation period dependence of the Curie temperature of the Ni/Fe multilayers.