Saturation Magnetistion

The room temperature hysteresis loops show the distinction between ferromagnetic, antiferromagnetic and weak ferromagnetic/uncoupled samples.

The samples with a $15\ensuremath{\unskip\,\mathrm{\AA{}}}$ iron layer thickness have the lowest volume magnetisation. Both the 20/15 and 27/15 samples have saturation magnetisations which are consistent within experimental error, of $230\pm50\ensuremath{\unskip\,\mathrm{\nicefrac{\mathrm{EMU}}{\mathrm{cm}^{3}}}}$ and $300\pm60\ensuremath{\unskip\,\mathrm{\nicefrac{\mathrm{EMU}}{\mathrm{cm}^{3}}}}$ respectively This is as expected as both samples show antiferromagnetic iron layer coupling in the magnetisation vs temperature scans and have the same iron layer thickness.

The 27/20 sample has a larger volume magnetisation than the samples with a $15\ensuremath{\unskip\,\mathrm{\AA{}}}$ iron layer thickness, of $500\pm60\ensuremath{\unskip\,\mathrm{\nicefrac{\mathrm{EMU}}{\mathrm{cm}^{3}}}}$. As the layer coupling is also antiferromagnetic in this case this is expected for a thicker magnetic layer. The 40/20 has the same iron layer thickness but has a much larger volume magnetisation than the 27/20 sample. The 40/20 sample has weakly ferromagnetic or uncoupled iron layers rather than the antiferromagnetically coupled layers in the 27/20 sample.

The 16/10 and 20/10 samples show larger than expected magnetisations at room temperature, of $700\pm160\ensuremath{\unskip\,\mathrm{\nicefrac{\mathrm{EMU}}{\mathrm{cm}^{3}}}}$ and $2100\pm500\ensuremath{\unskip\,\mathrm{\nicefrac{\mathrm{EMU}}{\mathrm{cm}^{3}}}}$ respectively. These samples have the thinnest iron layers and so would be expected to have a lower $T_{C}$ than the thicker layers and hence have a lower magnetisation at room temperature.

The saturation magnetisation values at room temperature reflect strongly the rapidity of the decrease in $M$ with temperature seen in Figures 7.1 to 7.5. Samples that show a relatively slow decrease in $M$ with $T$, such as the 20/10 and 40/20 samples, show the greatest saturation magnetisation at room temperature.

The antiferromagnetically coupled samples 16/10, 20/15, 27/15 and 27/20 show much smaller saturation magnetisations at room temperature. This separation in behaviour is likely to arise from the fact that at room temperature the aligning influence on the layers are either ferromagnetic in addition to the applied field for ferromagnetic layers, solely from the applied field for uncoupled layers and applied field against antiferromagnetic alignment for the layers coupled antiferromagnetically below $T_{N}$.