HoFe$_2$

As can be seen in Figure 6.3 the HoFe$_2$ film has a markedly different Mössbauer spectrum compared to YFe$_2$ and DyFe$_2$. Unfortunately this may not be a pure HoFe$_2$ spectrum as, due to the thinness of the sample layer, part of the spectrum will be recorded from the YFe$_2$ seed layer.

Using the CEMS theory outlined in Section 2.5.2 an upper limit can be placed on the relative spectral contributions from the two layers. For a $500\ensuremath{\unskip\,\mathrm{\AA{}}}$ sample layer the ratio of sample to seed layer is $55\%$:$45\%$. Thus the spectrum is more akin to that from a HoFe$_2$/YFe$_2$ bilayer. Hence we cannot analyse the spectrum to give any accurate information about a HoFe$_2$ thin film due to the overlap of the two sub-spectra and any possible interface effects.

In the $750\ensuremath{\unskip\,\mathrm{\AA{}}}$ DyFe$_2$ thin film this ratio is $85\%$:$15\%$ giving a more representative spectrum of the sample layer. In the YFe$_2$ thin film this effect does not apply as the sample and seed layer are the same material and continuous.