Successive spin reorientations and rare earth ordering in Nd0.5Dy0.5FeO3: Experimental and ab initio investigations

Article

关键词: TEMPERATURE SPECIFIC-HEAT;    NEUTRON-DIFFRACTION;    MAGNETIC-STRUCTURE;    ORTHOCHROMITES;    TRANSITIONS;   

DOI  :  10.1103/PhysRevB.102.144432

来源: SCIE

【 摘 要 】

In the present paper, 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 Fe3+ spins in Nd0.5Dy0.5FeO3 belongs to Gamma(4) irreducible representation (G(x), F-z) as observed in both parent compounds (NdFeO3 and DyFeO3). The neutron-diffraction study also confirms the presence of a spin-reorientation transition where the magnetic structure of Fe3+ spins changes from Gamma(4) to Gamma(2)(F-x, G(z)) representation between 75 and 20 K while maintaining a G-type antiferromagnetic configuration. Such a gradual spin reorientation is unusual since the large single ion anisotropy of Dy3+ ions is expected to cause an abrupt Gamma(4) -> Gamma(1)(G(y)) rotation of the Fe3+ spins. At 10 K, the Fe3+ magnetic structure is represented by Gamma(2) (F-x, G(z)). Unexpectedly, the Gamma(4) structure of Fe3+ spins re-emerges below 10 K, which also coincides with the development of rare-earth (Nd3+/Dy3+) magnetic ordering having c(y)(R) 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 Nd3+-Fe3+ and Nd3+-Dy3+ exchange interactions. These interactions suppress the independent rare-earth magnetic ordering observed in both parent compounds due to Nd3+/Dy3+-Nd3+/Dy3+ 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 (Nd3+/Dy3+), with Gamma(2) (Fx, Gz) configuration for Fe3+ moments, is energetically very close to a phase with the same rare-earth magnetic ordering but Gamma(4) (Gx, Fz) configuration of Fe3+ spins. Further, the Nd3+-Fe3+ and Nd3+-Dy3+ exchange interactions are observed to play significant roles in the complex Fe3+ spin reorientation with the re-emergence of Gamma(4) at low temperature. Consistent with the experimental observations, our calculations established the mixed phase (Gamma(2) and Gamma(4)) to be the magnetic ground state of Fe3+ moments.

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