학술논문
Synthesis, Structures, and Magnetic Properties ofRare-Earth Cobalt Arsenides, RCo2As2(R = La, Ce, Pr, Nd).
Document Type
Article
Author
Source
Subject
*RARE earth metal compound synthesis
*MAGNETIC properties of rare earth metals
*SINGLE crystals
*X-ray absorption near edge structure
*X-ray powder diffraction
*ELECTRONIC band structure
*TEMPERATURE effect
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Language
ISSN
0897-4756
Abstract
Four rare-earth cobalt arsenides,RCo2As2(R = La, Ce, Pr, Nd), were obtainedby reactions of constituentelements in molten Bi. The use of Bi flux also allowed the growthof representative single crystals. All compounds are isostructuraland belong to the ThCr2Si2type (space group I4/mmm). The formation of Co vacanciesis observed in all structures, while the structures of La- and Ce-containingcompounds also show incorporation of minor Bi defects next to theR crystallographic site. Correspondingly, the general formula of thesematerials can be written as R1–xBixCo2−δAs2, with x/δ = 0.03/0.1, 0.05/0.15, 0/0.2,and 0/0.3 for R = La, Ce, Pr, and Nd, respectively. All compoundsexhibit high-temperature ferromagnetic ordering of Co magnetic momentsin the range 60–200 K. Electronic band structure calculationsrevealed a high peak in the density of states at the Fermi level,thus supporting the itinerant nature of magnetism in the Co sublattice.The magnetic ordering in the lanthanide sublattice takes place atlower temperatures, with the R moments aligning antiparallel to theCo moments to give a ferrimagnetic ground state. The measurementson oriented single crystals demonstrated significant magnetic anisotropyin the ferrimagnetic state, with the preferred moment alignment alongthe caxis of the tetragonal lattice. Neutron powderdiffraction failed to reveal the structure of magnetically orderedstates but confirmed the presence of Co vacancies. X-ray absorptionnear-edge structure spectroscopy on Ce1.95Bi0.05Co1.85As2showed the average oxidation stateof Ce to be +3.06. Solid state NMR spectroscopy revealed a substantiallyreduced hyperfine field on the Co atoms in the vicinity of Bi defects. [ABSTRACT FROM AUTHOR]