Coexisting magnetic structures and spin-reorientation in Er${}_{0.5}$Dy${}_{0.5}$FeO${}_3$: Bulk magnetization, neutron scattering, specific heat, and \emph{Ab-initio} studies

Abstract

The complex magnetic structures, spin-reorientation and associated exchange interactions have been investigate in Er${}_{0.5}$Dy${}_{0.5}$FeO${}_3$ using bulk magnetization, neutron diffraction, specific heat measurements and density functional theory calculations. The Fe${}^{3+}$ spins order as G-type antiferromagnet structure depicted by ${\Gamma }_4$($G_x$,$A_y$,$F_z$) irreducible representation below 700K, similar to its end compounds. The bulk magnetization data indicate occurrence of the spin-reorientation and rare-earth magnetic ordering below $\sim$75 K and 10 K, respectively. The neutron diffraction studies confirm an "incomplete" ${\Gamma }_4$$\to$ ${\Gamma }_2$($F_x$,$C_y$,$G_z$) spin-reorientation initiated $\le$75 K. Although, the relative volume fraction of the two magnetic structures varies with decreasing temperature, both co-exist even at 1.5 K. At 8 K, Er${}^{3+}$/Dy${}^{3+}$ moments order as $c_y^R$ arrangement develop, which gradually increases in intensity with decreasing temperature. At 2 K, magnetic structure associated with $c_z^R$ arrangement of Er${}^{3+}$/Dy${}^{3+}$ moments also appears. At 1.5 K the magnetic structure of Fe${}^{3+}$ spins is represented by a combination of ${\Gamma }_2$+${\Gamma }_4$+${\Gamma }_1$, while the rare earth moments coexists as $c_y^R$ and $c_z^R$ corresponding to ${\Gamma }_2$ and ${\Gamma }_1$ representation, respectively. The observed Schottky anomaly at 2.5 K suggests that the "rare-earth ordering" is induced by polarization due to Fe${}^{3+}$ spins. The Er${}^{3+}$-Fe${}^{3+}$ and Er${}^{3+}$-Dy${}^{3+}$ exchange interactions, obtained from first principle calculations, primarily cause the complicated spin-reorientation and $c_y^R$ rare-earth ordering, respectively, while the dipolar interactions between rare-earth moments, result in the $c_z^R$ type rare-earth ordering at 2 K.

15 pages, 11 figures

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