Structural and magnetic transitions in PbV 6 O 11
2001; American Physical Society; Volume: 64; Issue: 17 Linguagem: Inglês
10.1103/physrevb.64.174404
ISSN1095-3795
AutoresOlivier Mentré, Y. Kanke, A-C. Dhaussy, P. Conflant, Yoshiaki Hata, Eiji Kita,
Tópico(s)Catalysis and Oxidation Reactions
Resumo${\mathrm{PbV}}_{6}{\mathrm{O}}_{11}$ was prepared as a single phase using a high-pressure high-temperature synthesis allowing a wide characterization of its structural and magnetic properties using both single crystals and polycrystalline samples. It crystallizes in hexagonal ${P6}_{3}\mathrm{mc}$ at room temperature, whereas in hexagonal ${P6}_{3}/mmc$ above ${T}_{t}=560\mathrm{K}.$ No charge distribution change was evidenced on the transition. The symmetry centers loss is accompanied by a drastic change within the kagom\'e lattice formed by vanadium atoms commonly labeled V(1). In the same way, a phenomenon discussed in terms of V(1) energy gap is evidenced below ${T}_{t}$ on the inverse magnetic susceptibility. Below ${T}_{C}=91.2\mathrm{K},$ ${\mathrm{PbV}}_{6}{\mathrm{O}}_{11}$ shows uniaxial magnetic anisotropy with an easy axis of magnetization parallel to the [001] direction. The saturated magnetization was successfully analyzed using a linear ${M}_{s}^{2}$ versus ${T}^{2}$ law leading to ${M}_{s}=1.95\ensuremath{\mu}\mathrm{B}/\mathrm{f}.\mathrm{u}.$ at 0 K. This value is very close to the integer value of 2, which would involve two effective ${\mathrm{V}}^{4+}$ or one ${\mathrm{V}}^{3+}$ electrons in the ordered state, in agreement with the V(1) negligible spin moment at low temperatures. Therefore, the matching of such a plot suggests that the mechanism of magnetization is spin fluctuation. Finally, a third magnetic transition is observed around 40 K accompanied by a intense peak of the thermal Seebeck curve.
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