Comment on “Spin crossover in (Mg,Fe)O: A Mössbauer effect study with an alternative interpretation of x-ray emission spectroscopy data”

In a recent paper, Kantor et al. presented Mössbauer spectroscopy data on the pressure dependence of the Fe spin state in ${\mathrm{Mg}}_{1-x}{\mathrm{Fe}}_x\mathrm{O}$ [Phys. Rev. B 73, 100101(R) (2006)] and found that the transition was completed at significantly higher pressures than what had been found by x-ray emission spectroscopy (XES) studies. In order to account for the discrepancy, the authors reanalyzed the XES spectra using a simple spectral decomposition and achieved good agreement for the two types of data. In this paper, we show that the proposed alternative analysis of the XES spectra is inadequate, prove that previous XES work had correctly identified the low-spin state at the highest pressures, and provide a complete reanalysis of the XES data.

Figure 1

(Color online) Experimental (left panel) and theoretical (right panel) $K\beta$ spectra of $\left[\mathrm{Fe}{\left(\mathrm{phen}\right)}_2{\left(\mathrm{NCS}\right)}_2\right]$, in its HS (top) and LS (bottom) forms. Insets in the experimental part display the Mössbauer spectra.

Figure 2

(Color online) Four spectra on the spin transition of $\left[\mathrm{Fe}{\left(\mathrm{phen}\right)}_2{\left(\mathrm{NCS}\right)}_2\right]$. Differences from the LS line shape are also shown below the spectra.

Figure 3

(Color online) Left: fitting of the LS data with the model of Kantor et al. Right: the LS data convoluted with a Gaussian of $2.2\mathrm{eV}$ FWHM compares well with the $79\mathrm{GPa}$ ${\mathrm{Mg}}_{0.75}{\mathrm{Fe}}_{0.25}\mathrm{O}$ spectrum from Ref. 6.

Figure 4

(Color online) Selected spectra reflecting the spin transition in ${\mathrm{Mg}}_{0.75}{\mathrm{Fe}}_{0.25}\mathrm{O}$ from Ref. 6. Differences from the LS reference are also shown.

Figure 5

(Color online) Comparison of the different analyses of the ${\mathrm{Mg}}_{0.75}{\mathrm{Fe}}_{0.25}\mathrm{O}$ XES data.