Coexistence of double alternating antiferromagnetic chains in (VO)_2P_2O_7 : NMR study

TL;DR

This study uses NMR to reveal that (VO)_2P_2O_7 contains two independent antiferromagnetic chains with distinct spin gaps, indicating separate magnetic excitations linked to different V chains, aligning with neutron scattering results.

Contribution

It demonstrates the coexistence of two magnetic subsystems with different spin gaps in (VO)_2P_2O_7, providing detailed NMR analysis and linking structural differences to magnetic properties.

Findings

Two independent spin components with gaps of 35 K and 68 K.

Confirmation of two magnetic subsystems via NMR and neutron scattering.

Differences in V-V distances influence exchange interactions.

Abstract

Nuclear magnetic resonance (NMR) of 31P and 51V nuclei has been measured in a spin-1/2 alternating-chain compound (VO)_2P_2O_7. By analyzing the temperature variation of the 31P NMR spectra, we have found that (VO)_2P_2O_7 has two independent spin components with different spin-gap energies. The spin gaps are determined from the temperature dependence of the shifts at 31P and 51V sites to be 35 K and 68 K, which are in excellent agreement with those observed in the recent inelastic neutron scattering experiments [A.W. Garrett et al., Phys. Rev. Lett. 79, 745 (1997)]. This suggests that (VO)_2P_2O_7 is composed of two magnetic subsystems showing distinct magnetic excitations, which are associated with the two crystallographically-inequivalent V chains running along the b axis. The difference of the spin-gap energies between the chains is attributed to the small differences in the V-V distances, which may result in the different exchange alternation in each magnetic chain. The exchange interactions in each alternating chain are estimated and are discussed based on the empirical relation between the exchange interaction and the interatomic distance.