Fe-spin reorientation in PrFeAsO : Evidences from resistivity and specific heat studies

We report the magnetic field dependence of resistivity ($\rho$) and specific heat ($C$) for the non-superconducting PrFeAsO compound. Our study shows a hitherto unobserved anomaly at $T_{SR}$ in the resistivity and specific heat data which arises as a result of the interplay of antiferromagnetic (AFM) Pr and Fe sublattices. Below the AFM transition temperature ($T_N^{\mathrm{P}\mathrm{r}}$), Pr moment orders along the crystallographic c axis and its effect on the iron subsystem causes a reorientation of the ordered inplane Fe moments in a direction out of the $ab$ plane. Application of magnetic field introduces disorder in the AFM Pr sublattice, which, in turn, reduces the out-of-plane Pr-Fe exchange interaction responsible for Fe spin reorientation. Both in $\rho$($T$) and $d(C\mathrm{/}T)\mathrm{/}dT$ curves, the peak at $T_{SR}$ broadens with the increase of $H$ due to the introduction of the disorder in the AFM Pr sublattice by magnetic field. In $\rho$($T$) curve, the peak shifts towards lower temperature with $H$ and disappears above 6 T while in $d(C\mathrm{/}T)\mathrm{/}dT$ curve the peak remains visible up to 14 T. The broadening of the anomaly at $T_N^{\mathrm{P}\mathrm{r}}$ in $C(T)$ with increasing $H$ further confirms that magnetic field induces disorder in the AFM Pr sublattice.