Magnetic transition in MoO3: Influence of Mo5+/Mo6+ ratios on paramagnetic to diamagnetic behavior

Abstract

This study examines the transition from paramagnetic to diamagnetic response in MoO₃, a phenomenon previously documented in the literature where the magnetic response of MoO₃ varies with the applied field, changing from paramagnetic at low fields to diamagnetic at high fields. MoO₃ samples were synthesized with controlled Mo⁶⁺/Mo⁵⁺ ratios while maintaining high crystallinity to elucidate this phenomenon. The samples were prepared in a chemical vapor deposition (CVD) furnace under an oxygen environment at two different temperatures, 550 and 650 °C, and two annealing times, 4 and 8 h. The resulting samples were subjected to characterization using powder X-ray diffraction (XRD), Raman spectroscopy, Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), and vibrating sample magnetometry (VSM). The XRD results demonstrated the formation of highly crystalline MoO₃ in all samples, which is confirmed by Raman and FTIR. The XPS results demonstrate the concentration of Mo⁵⁺ and Mo⁶⁺ present in each sample. The results of the VSM experiments demonstrated that the observed change in the magnetic response of MoO₃ is due to the intensity of the material's response being comparable to that of the sample holder's response. Moreover, vibrating sample magnetometry and X-ray photoelectron spectroscopy analysis revealed that MoO₃ can exhibit both paramagnetic and diamagnetic behavior, depending on the quantity of Mo⁵⁺ present in the sample.