Successive spin reorientations and rare earth ordering in Nd0.5Dy0.5FeO3 : Experimental and ab initio investigations (original) (raw)
In present study, the magnetic structure and spin reorientation of mixed rare-earth orthoferrite Nd0.5Dy0.5FeO3 have been investigated. At room temperature, our neutron diffraction measurements reveal that the magnetic structure of Fe 3+ spins in Nd0.5Dy0.5FeO3 belongs to Γ4 irreducible representation (Gx, Fz) as observed in both parent compounds (NdFeO3 and DyFeO3). The neutron diffraction study also confirms the presence of spin reorientation transition where magnetic structure of Fe 3+ spins changes from Γ4 to Γ2(Fx, Gz) representation between 75 and 20 K while maintaining G-type antiferromagnetic configuration. Such a gradual spin reorientation is unusual since the large single ion anisotropy of Dy 3+ ions is expected to cause an abrupt Γ4→ Γ1(Gy) rotation of the Fe 3+ spin. Between 20 and 10 K, the Fe 3+ magnetic structure is represented by Γ2 (Fx, Gz). Unexpectedly, Γ4 structure of Fe 3+ spins re-emerges below 10 K which also coincides with the development of rare-earth (Nd 3+ /Dy 3+) magnetic ordering having c R y configuration. Such re-emergence of a magnetic structure has been a rare phenomenon in orthoferrites. The absence of a second order phase transition in rare-earth ordering, interpreted from heat capacity data, suggests the prominent role of Nd 3+-Fe 3+ and Nd 3+-Dy 3+ exchange interactions. These interactions suppress the independent rare-earth magnetic ordering observed in both parent compounds due to Nd 3+ /Dy 3+-Nd 3+ /Dy 3+ exchange interactions. Our density functional theory calculations including Coulomb correlation and spin-orbit interaction effects (DFT+U +SO) reveal that the C-type arrangement of rare-earth ions (Nd 3+ /Dy 3+), with Γ2 (Fx, Gz) configuration for Fe 3+ moments, is the ground state whereas a combination of C-type magnetic ordering (rare-earth) and Γ4 (Gx, Fz) configuration of Fe 3+ spins is energetically very close to the ground state. Further, the Nd 3+-Fe 3+ and Nd 3+-Dy 3+ exchange interactions are observed to play significant roles in the complex Fe 3+ spin reorientation with the re-emergence of Γ4 at low temperature.
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