Successive spin reorientations and rare earth ordering in Nd 0.5 Dy 0.5 Fe O 3 : Experimental and ab initio investigations

摘要: In the present paper, magnetic structure and spin reorientation of mixed rare-earth orthoferrite ${\mathrm{Nd}}_{0.5}{\mathrm{Dy}}_{0.5}\mathrm{Fe}{\mathrm{O}}_{3}$ have been investigated. At room temperature, our neutron-diffraction measurements reveal that ${\mathrm{Fe}}^{3+}$ spins in belongs to ${\mathrm{\ensuremath{\Gamma}}}_{4}$ irreducible representation (${G}_{x}, {F}_{z}$) as observed both parent compounds ($\mathrm{Nd}\mathrm{Fe}{\mathrm{O}}_{3}$ $\mathrm{Dy}\mathrm{Fe}{\mathrm{O}}_{3}$). The study also confirms presence a spin-reorientation transition where changes from ${\mathrm{\ensuremath{\Gamma}}}_{2}({F}_{x}, {G}_{z}$) between 75 20 K while maintaining G-type antiferromagnetic configuration. Such gradual is unusual since large single ion anisotropy ${\mathrm{Dy}}^{3+}$ ions expected cause an abrupt ${\mathrm{\ensuremath{\Gamma}}}_{4}\ensuremath{\rightarrow}\phantom{\rule{4pt}{0ex}}{\mathrm{\ensuremath{\Gamma}}}_{1}({G}_{y}$) rotation spins. 10 K, represented by ${\mathrm{\ensuremath{\Gamma}}}_{2}$ (${F}_{x}, {G}_{z}$). Unexpectedly, re-emerges below which coincides with development (${\mathrm{Nd}}^{3+}/{\mathrm{Dy}}^{3+}$) ordering having ${c}_{y}^{R}$ re-emergence has rare phenomenon orthoferrites. absence second-order phase ordering, interpreted heat capacity data, suggests prominent role ${\mathrm{Nd}}^{3+}\ensuremath{-}{\mathrm{Fe}}^{3+}$ ${\mathrm{Nd}}^{3+}\ensuremath{-}{\mathrm{Dy}}^{3+}$ exchange interactions. These interactions suppress independent due ${\mathrm{Nd}}^{3+}/{\mathrm{Dy}}^{3+}\ensuremath{-}{\mathrm{Nd}}^{3+}/{\mathrm{Dy}}^{3+}$ Our density-functional-theory calculations including Coulomb correlation spin-orbit interaction effects ($\mathrm{DFT}+U+\mathrm{SO}$) C-type arrangement (${\mathrm{Nd}}^{3+}/{\mathrm{Dy}}^{3+}$), configuration for moments, energetically very close same but Further, are play significant roles complex at low temperature. Consistent experimental observations, established (${\mathrm{\ensuremath{\Gamma}}}_{2}$ ${\mathrm{\ensuremath{\Gamma}}}_{4}$) be ground state moments.