51V-NMR study of charge order induced by cation order in δ-Ag2/3V2O5

Y Kawasaki,M Isobe,Y Ueda,T Yamauchi,T Baba,T Mito,K Nakamura,K Nishiyama,T Koyama,Y Kishimoto,R Morioka

doi:10.1088/1742-6596/807/6/062001

Abstract

51V-NMR experiments have been performed to investigate the local magnetic and electronic properties of the mixed-valence oxide δ-Ag2/3V2O5, which shows the novel V4+/V5+ charge ordering trigged by Ag ion ordering. We have observed the abrupt loss of 51V-NMR signal coming from the non-magnetic V5+-like ions above Tc = 225 K. It indicates that the majority of V ions are magnetic above Tc and that the phase transition is accompanied by the charge separation and the charge ordering of 3d electrons on V sites. In the low-temperature phase below Tc, the nuclear spin-lattice relaxation rate 1/T1 shows the thermal activation-type temperature dependence with the activation energy of about 130 K. It has been clarified that the ground state of this material is the charge ordered one with the spin singlet of 3d electrons on V4+-V4+ pair from a microscopic point of view.

Highlights

Various exotic phenomena due to spin, charge, lattice and orbital degrees of freedom have attracted much attention in strongly correlated electron systems [1]
We focus on δ-Ag2/3V2O5, which shows the novel charge ordering induced by cation ordering [11]
The magnetic susceptibility shows a broad maximum at around 110 K followed by spin-gapped behavior, in contrast to Curie-Weiss behavior above the transition temperature. These results indicate that the magnetic V4+ ions have a specific geometrical arrangement required for the spin-gap state and that the geometrical arrangement is closely related to the Ag ion ordering

Summary

Introduction

Various exotic phenomena due to spin, charge, lattice and orbital degrees of freedom have attracted much attention in strongly correlated electron systems [1]. Spin-echo intensity as a function of external field at the fixed frequency of 67.1 MHz. For the measurements of the nuclear spin-lattice relaxation rate 1/T1, we used the saturation recovery method.

Results

Conclusion