Crystal structure and magnetic ordering of the rare-earth and Cu moments in [ital R]Ba[sub 2]Cu[sub 2]NbO[sub 8] ([ital R]=Nd,Pr)

Journal Article · Tue Jun 01 00:00:00 EDT 1993 · Physical Review, B: Condensed Matter; (United States)

DOI:https://doi.org/10.1103/PhysRevB.47.15256· OSTI ID:6786834

Rosov, N; Lynn, J W ^[1]; Radousky, H B; Bennahmias, M ^[2]; Goodwin, T J; Klavins, P; Shelton, R N ^[3]

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1. Reactor Radiation Division, National Institute of Standards and Technology, Gaithersburg, Maryland 20899 (United States) Center for Superconductivity Research, Department of Physics, University of Maryland, College Park, Maryland 20742 (United States)
2. University of California, Lawrence Livermore National Laboratory, Livermore, California 94550 (United States)
3. Department of Physics, University of California, Davis, California 95616 (United States)

Using neutron diffraction, we have studied the crystal structure and magnetic ordering of the rare-earth and Cu moments in the layered perovskite systems NdBa[sub 2]Cu[sub 2]NbO[sub 8] (Nd 2:2:1:8) and PrBa[sub 2]Cu[sub 2]NbO[sub 8] (Pr 2:2:1:8). These are systems similar to [ital R]Ba[sub 2]Cu[sub 3]O[sub 6+[ital x]] [[ital R] 1:2:3:(6+[ital x])] for which the chain Cu-O layers have been fully replaced by layers of Nb-O octahedra. Powder profile refinements below 20 K show that both Nd 2:2:1:8 and Pr 2:2:1:8 are in space group [ital I]4/[ital mcm], because the near-neighbor Nb-O octahedra are rotated about the [ital c] axis in opposite senses. The Cu moments are ordered below 375(10) K for Nd 2:2:1:8 and 340(15) K for Pr 2:2:1:8, with saturation moments in both cases of 0.5(1)[mu][sub [ital B]]. The near-neighbor Cu spins are aligned antiparallel, just as for the Cu plane'' ordering in [ital R] 1:2:3:(6+[ital x]). The rare-earth moments order at 1.69(5) and 12.6(1) K for Nd 2:2:1:8 and Pr 2:2:1:8, respectively, with saturated values of [l angle][mu][sub [ital z]][r angle]=0.74(5)[mu][sub [ital B]] and 1.2(1)[mu][sub [ital B]]. The near-neighbor [ital R] spins, both in the [ital ab] plane and along the [ital c] axis, are also aligned antiparallel. As in the case of Pr 1:2:3:(6+[ital x]), the Pr sublattice of Pr 2:2:1:8 has an ordering temperature that is much higher than other rare-earth moments in these layered perovskites, suggesting that the Pr in Pr 2:2:1:8 experiences the same [ital f]-electron hybridization as has been observed in Pr 1:2:3:(6+[ital x]). The rare-earth ordering of both Nd 2:2:1:8 and Pr 2:2:1:8 is not completely three-dimensional in nature: rather, the ordering within the [ital a]-[ital b] plane is two-dimensional with only short-range order along the [ital c] axis. The presence of oxygen defects appears to affect the [ital c]-axis correlation length.

• DOE Contract Number: W-7405-ENG-48
• OSTI ID: 6786834
• Journal Information: Physical Review, B: Condensed Matter; (United States), Vol. 47:22; ISSN 0163-1829
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
BARIUM OXIDES
MAGNETIC PROPERTIES
COPPER OXIDES
NEODYMIUM OXIDES
NIOBIUM OXIDES
PRASEODYMIUM OXIDES
CRYSTAL STRUCTURE
HIGH-TC SUPERCONDUCTORS
NEUTRON DIFFRACTION
ORDER-DISORDER TRANSFORMATIONS
TEMPERATURE RANGE 0000-0013 K
TEMPERATURE RANGE 0013-0065 K
ALKALINE EARTH METAL COMPOUNDS
BARIUM COMPOUNDS
CHALCOGENIDES
COHERENT SCATTERING
COPPER COMPOUNDS
DIFFRACTION
NEODYMIUM COMPOUNDS
NIOBIUM COMPOUNDS
OXIDES
OXYGEN COMPOUNDS
PHASE TRANSFORMATIONS
PHYSICAL PROPERTIES
PRASEODYMIUM COMPOUNDS
RARE EARTH COMPOUNDS
REFRACTORY METAL COMPOUNDS
SCATTERING
SUPERCONDUCTORS
TEMPERATURE RANGE
TRANSITION ELEMENT COMPOUNDS
360202* - Ceramics
Cermets
& Refractories- Structure & Phase Studies
360204 - Ceramics
Cermets
& Refractories- Physical Properties