FM-AFM crossover in vanadium oxide nanomaterials

The magnetic properties of nanomaterials based on vanadium oxide (multiwall nanotubes, nanorods, and nanolayers) have been investigated in the temperature range of 1.8–220 K by high-frequency (60-GHz) EPR. A transition from a ferromagnetic temperature dependence to an antiferromagnetic temperature dependence has been observed in nanorods and nanotubes with a decrease in the temperature. The FM-AFM crossover observed near T _C ~ 110 K is accompanied by a low-temperature increase in the Curie constant by a factor of 2.7–7. The comparison of the experimental data for various VO _x nanoparticles indicates that the most probable cause of the change in the type of magnetic interaction is a change in the concentration of V⁴⁺ magnetic ions.