An evidence of local structural disorder across spin-reorientation transition in DyFeO₃ : An Extended X-ray Absorption Fine structure (EXAFS) study.

The present work is aimed at exploring the local atomic structure modifications related to the spin reorientation transition (SRT) in DyFeO$_3$ orthoferrite exploiting x-ray absorption fine structure (XAFS) spectroscopy. For this purpose we studied by XAFS the evolution of the local atomic structure around Fe and Dy as function of temperature (10-300 K) in a DyFeO$_3$ sample having the SRT around 50-100K. For sake of comparison we studied a YFeO$_3$ sample having no SRT. The analysis of the extended region (EXAFS) has revealed an anomalous trend of Fe-O nearest neighbour distribution in DFO revealing i) a weak but significant compression with increasing temperature above the SRT and ii) a peculiar behavior of mean square relative displacement (MSRD) [$\sigma^2$] of Fe-O bonds showing an additional static contribution in the low temperature region, below the SRT. These effects are absent in the YFO sample supporting these anomalies related to the SRT. Interestingly the analysis of Dy $L_3$-edge data also reveal anomalies in the Dy-O neighbour distribution associated to the SRT, pointing out a role of magnetic \emph{Re} ions across $\mathrm{T_{SRT,Fe}}$. These results point out micro-structural modification at both Fe and Dy sites associated to the magnetic transitions in DFO, it can be stated in general terms that such local distortions across $\mathrm{Fe^{3+}}$ and magnetic \emph{Re}$^{3+}$ may be present in other orthoferrites exhibiting multiferroic nature.