Pressure-Induced Collapse of Magnetic Order in Jarosite

We report a pressure-induced phase transition in the frustrated kagomé material jarosite at $\sim 45\mathrm{GPa}$, which leads to the disappearance of magnetic order. Using a suite of experimental techniques, we characterize the structural, electronic, and magnetic changes in jarosite through this phase transition. Synchrotron powder x-ray diffraction and Fourier transform infrared spectroscopy experiments, analyzed in aggregate with the results from density functional theory calculations, indicate that the material changes from a $R\overline{3}m$ structure to a structure with a $R\overline{3}c$ space group. The resulting phase features a rare twisted kagomé lattice in which the integrity of the equilateral ${\mathrm{Fe}}^{3+}$ triangles persists. Based on symmetry arguments we hypothesize that the resulting structural changes alter the magnetic interactions to favor a possible quantum paramagnetic phase at high pressure.

Figure 1

The normalized lattice parameters for jarosite at ambient temperature are plotted as a function of pressure (top). These values were obtained from Pawley fits of the PXRD data using the $R\overline{3}m$ space group for the jarosite phase. The plot of $c/a$ vs pressure highlights the phase transitions at $P^{*,1}$ and $P^{*,2}$. The spline interpolation in the plot of $c/a$ vs pressure, which lies behind the data points over the entire measure pressure range, is a guide for the eye. Unless shown, error bars are commensurate with the symbol size. The dashed lines in the figure (top) are the normalized equation of state curves for the volume data (see Table S3 for parameters and Figs. S3–S6 in the Supplemental Material [46].).

Figure 2

The normalized XES data (left) illustrate that the electronic structure changes linearly with pressure, as shown by the plot of the IAD value vs pressure in the inset of the XES plot. The data from jarosite measured at 1.1 GPa overlays the high-spin ${\mathrm{Fe}}^{3+}$ reference data. In the plot of the IAD values, closed symbols originate from spectra reported herein, whereas open symbols originate from previously reported spectra [42]. The SMS data (center) show a change in spectral shape between 39.5 and 45.6 GPa. Spurious signals in the SMS data above 80 GPa are masked between 36 and 41 ns. Open circles denote the data points while the solid lines show the fits to these data. Fits of the data reveal a first order discontinuity in $\mathrm{\Delta }{E}_Q$ (right), which decreases from 2.24(2) to $1.62(2)\mathrm{mm}{\mathrm{s}}^{-1}$ through the phase transition at 43.7(4) GPa. Unless shown, error bars are commensurate with the symbol size. Open gray circles are previously reported data for the $\mathrm{\Delta }{E}_Q$ plot [42]. See Fig. S23 in the Supplemental Material [46] for an enlarged plot of the IAD values as a function of pressure.

Figure 3

The temperature-pressure magnetic phase diagram for jarosite up to 121 GPa. Closed symbols denote antiferromagnetic order. Open symbols denote measurements in which no magnetic ordering is observed. The antiferromagnetic region is highlighted in blue while the paramagnetic region is highlighted in pink. In the legend, AFM denotes antiferromagnetic ordering, while PM denotes paramagnetic. The measured values from a previous study are reported in Ref. [42]. The dashed lines indicate the linear trajectory of $T_N$ with pressure and the maximum measured $T_N$ value. In the inset, blue equilateral triangles and distorted pink hexagons highlight the twisted kagomé lattice of ${\mathrm{Fe}}^{3+}$ ions at 80 GPa in the $R\overline{3}c$ phase. Iron and oxygen ions are depicted as orange and red spheres, respectively, while the other atoms are omitted for clarity.