Structural and magnetic transitions in PbV6O11 -: art. no. 174404

PbV6O11 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)mc at room temperature, whereas in hexagonal P6(3)/mmc above T-t = 560 K. No charge distribution change was evidenced on the transition. The symmetry centers loss is accompanied by a drastic change within the kagome 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 K, PbV6O11 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 muB/f.u. at 0 K. This value is very close to the integer value of 2, which would involve two effective V4+ or one V3+ 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.