Concentration and temperature dependence of magnetic susceptibilities in lithium vanadium oxide bronzes in the cryogenic region
Abstract
A series of β-phase lithium vanadium oxide bronzes, Li xV 2O 5, ranging in lithium content from x = 0.25 to x = 0.49, have been measured by the Gouy method from 1.2°K to 300°K. Although the data above 60°K can be represented by laws of the Curie-Weiss type with negative Weiss temperatures, below 60°K the effective magnetic moment defined by (χT) {1}/{2} rapidly goes to zero as T approaches zero. Over the entire range of temperature studied the μeff vs. T curve can be calculated from a ligand-field model in which V 4+ levels are split by the combined effect of axial distortion and spin-orbit coupling to yield a lowest-lying nonmagnetic Γ6( E) state. As lithium content increases, the spin-orbit coupling constant is observed to increase from 0.012 eV to 0.021 eV, the electron localization to decrease from 0.9 to 0.6, and the axial distortion to remain essentially unchanged at about 0.007 eV. A discontinuous transition from localized to collective electron behavior is predicted at x = 0.37, but no such discontinuity appears in the magnetic behavior. However, there are observed small inflections in the χ-1 vs. T curve in the range 7-10°K when x exceeds 0.35, which suggest incipient antiferromagnetic ordering, but these inflections are not evident in the μeff vs. T curve. When x exceeds 0.35, a small break also appears in the χ-1 vs. T curve at 170°K. As supported by DTA measurements, imperceptible structure changes may be occurring which the system adopts to avoid a metallic transition.
- Publication:
-
Journal of Solid State Chemistry France
- Pub Date:
- January 1970
- DOI:
- 10.1016/0022-4596(70)90007-1
- Bibcode:
- 1970JSSCh...1..152K