The spin-singlet states in the double trellis-layer bronzesNa0.56V2O5 with a uniformvalence and Sr0.5V2O5 with a valence order

Abstract

The structural, transport and magnetic properties of theδ-phasebronzes Na0.56V2O5 and Sr0.5V2O5 with double trellis layers have been explored by means of x-ray diffraction and throughmeasurements of electrical resistivity, thermoelectric power, magnetization and electronspin resonance. The properties of the Na compound with a uniform valence depend on thecooling rate likely due to the configuration for the order of Na: the slow cooling conditiongives rise to a thermal hysteresis for the semiconducting transport and the spin-singletstate due to the large exchange coupling for the rung in the trellis layer. On the otherhand, fast cooling leads to the absence of hysteresis and the metastable spin statedepending on the measurement time. The Sr compound with a valence order close toV4+ and V5+ is insulating due to electron correlation, and it exhibits the singlet state originating fromthe alternating-exchange chain effect.