Spin fluctuations in the antiferromagnetic metal Nb12O29

We report a comprehensive study of the monoclinic Nb12O29 that includes material synthesis, chemical and structural characterization, and measurements of physical properties as a function of temperature, magnetic field, and high pressure. The high-pressure structural study has been carried out up to 71 kbar. Critical behavior analysis of ρ(T) and Cp(T) as TN is approached from TN+ is consistent with the picture of localized spins in this metallic antiferromagnet. These results also indicate that thermally driven critical fluctuations are confined to a temperature range in the vicinity of TN≈12 K. The thermoelectric power, however, is strongly enhanced at T<70 K. The peculiar temperature dependence of the thermoelectric-power enhancement at low temperatures is consistent with predictions based on quantum critical fluctuations. We have also shown that the enhancement is suppressed under either a magnetic field or hydrostatic pressure.