Magnetic properties of vanadium-oxide nanotubes probed by static magnetization and {51}V NMR

TL;DR

This study investigates the magnetic behavior of vanadium-oxide nanotubes using static magnetization and {51}V NMR, revealing complex low-dimensional magnetic interactions, spin gaps, and mixed valency effects.

Contribution

It provides new insights into the magnetic structure and interactions in vanadium-oxide nanotubes, highlighting the presence of antiferromagnetic dimers, trimers, and nonmagnetic ions.

Findings

Approximately 30% of vanadium ions form dimers with a 700 K spin gap.

About 30% of ions are individual spins or trimers, indicating diverse magnetic states.

Remaining 40% of vanadium ions are nonmagnetic.

Abstract

Measurements of the static magnetic susceptibility and of the nuclear magnetic resonance of multiwalled vanadium-oxide nanotubes are reported. In this nanoscale magnet the structural low-dimensionality and mixed valency of vanadium ions yield a complex temperature dependence of the static magnetization and the nuclear relaxation rates. Analysis of the different contributions to the magnetism allows to identify individual interlayer magnetic sites as well as strongly antiferromagnetically coupled vanadium spins (S = 1/2) in the double layers of the nanotube's wall. In particular, the data give strong indications that in the structurally well-defined vanadium-spin chains in the walls, owing to an inhomogeneous charge distribution, antiferromagnetic dimers and trimers occur. Altogether, about 30% of the vanadium ions are coupled in dimers, exhibiting a spin gap of the order of 700 K, the other ~ 30% comprise individual spins and trimers, whereas the remaining \~ 40% are nonmagnetic.