Experimental Study on Interlayer Magnetic Coupling in Sputtered Al/Fe/Al/Gd Magnetic Multilayer Films: II. Hysteresis Curves of X-ray Magnetic Circular Dicroism at the Gd-$L_{3}$ Edge

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The spacer thickness dependence of the interlayer magnetic coupling (IMC) between Gd and Fe layers separated by Al spacers has been studied. Magnetization measurement and X-ray magnetic circular dicroism (XMCD) spectroscopy at the Gd-$L_{3}$ edge have been carried out on sputtered Fe (20 Å)/Al ($R$ Å)/Gd (40 Å) multilayer films (MLFs) for $R = 0$, 5, 10, and 100 and on some reference films. Experimental data at low magnetic fields below 1 kOe are carefully investigated. A simple theoretical model is introduced to evaluate the strength of IMC. The energy of IMC is represented by the term $J \mathbf{M}_{\text{Fe}} \cdot \mathbf{M}_{\text{Gd}}$, in which $\mathbf{M}_{\text{Fe}}$ and $\mathbf{M}_{\text{Gd}}$ denote the average overall magnetic moments of Fe and Gd layers, respectively. It is found that $J$, which is evaluated from the magnetization curves and the Gd-XMCD signals, is $370 \times 10^{4}$ Oe$\cdot$cm2/emu for MLF of $R = 0$, and can be reduced by one order of magnitude when $R$ is changed from 0 to 10. Most of characteristic features of the experimental data are ascribed to the varing magnetization of Gd layers. It is found that 40 Å Gd layers, which are paramagnetic at 5 K when isolated using 100 Å Al spacers, show magnetic hysteresis when sandwiched between Fe layers.
2010-06-15