Synthesis, structure, and ferromagnetism of the oxygen defect pyrochlore system Lu{sub 2}V{sub 2}O{sub 7-x} (x=0.40-0.65)

Journal Article · Wed Aug 01 00:00:00 EDT 2007 · Physical Review. B, Condensed Matter and Materials Physics

DOI:https://doi.org/10.1103/PHYSREVB.76.054439· OSTI ID:21055107

Knoke, G T; Niazi, A; Hill, J M; Johnston, D C ^[1]

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1. Ames Laboratory and Department of Physics and Astronomy, Iowa State University, Ames, Iowa 50011 (United States)

A fcc oxygen defect pyrochlore structure system Lu{sub 2}V{sub 2}O{sub 7-x} with x=0.40-0.65 was synthesized from the known fcc ferromagnetic semiconductor pyrochlore compound Lu{sub 2}V{sub 2}O{sub 7} which can be written as Lu{sub 2}V{sub 2}O{sub 6}O{sup '} with two inequivalent oxygen sites O and O{sup '}. Rietveld x-ray diffraction refinements show significant Lu-V antisite disorder for x > or approx. 0.5. The lattice parameter versus x (including x=0) shows a distinct maximum at x{approx}0.4. We propose that these observations can be explained if the oxygen defects are on the O{sup '} sublattice of the structure. The magnetic susceptibility versus temperature exhibits Curie-Weiss behavior above 150 K for all x, with a Curie constant C that increases with x as expected in an ionic model. However, the magnetization measurements also show that the (ferromagnetic) Weiss temperature {theta} and the ferromagnetic ordering temperature T{sub C} both strongly decrease with increasing x instead of increasing as expected from C(x). The T{sub C} decreases from 73 K for x=0 to 21 K for x=0.65. Furthermore, the saturation moment at a field of 5.5 T at 5 K is nearly independent of x, with the value expected for a fixed spin 1/2 per V. The latter three observations suggest that Lu{sub 2}V{sub 2}O{sub 7-x} may contain localized spin 1/2 vanadium moments in a metallic background that is induced by oxygen defect doping, instead of being a semiconductor as suggested by the C(x) dependence. We present evidence of magnetic granularity in Lu{sub 2}V{sub 2}O{sub 7-x} with increasing x, due to the random distribution of oxygen vacancies and associated Lu-V antisite mixing. For x=0.65, isothermal magnetization versus magnetic field M(H) and low-field M(T) measurements indicate the formation of interacting nanoscopic ferromagnetic domains below T{sub C}.

• OSTI ID: 21055107
• Journal Information: Physical Review. B, Condensed Matter and Materials Physics, Vol. 76, Issue 5; Other Information: DOI: 10.1103/PhysRevB.76.054439; (c) 2007 The American Physical Society; Country of input: International Atomic Energy Agency (IAEA); ISSN 1098-0121
• Country of Publication: United States
• Language: English

Related Subjects

75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
DEFECTS
FCC LATTICES
FERROMAGNETISM
LATTICE PARAMETERS
LUTETIUM COMPOUNDS
MAGNETIC FIELDS
MAGNETIC SUSCEPTIBILITY
MAGNETIZATION
OXYGEN
PYROCHLORE
SEMICONDUCTOR MATERIALS
SPIN
SYNTHESIS
TEMPERATURE DEPENDENCE
VACANCIES
VANADIUM
VANADIUM OXIDES
X-RAY DIFFRACTION