Some peculiarities of room-temperature ferromagnetism in ensembles of mixed-phase TiNx-TiOy nanoparticles

Abstract

Mixed-phase TiNx-TiOy nanoparticles with an average particlesize of 27–120 nm were prepared by the levitation-jet generator through condensation of Ti metal vapor in inert gas flow with gaseous nitrogen/air additive. The nanoparticles were characterized by Scanning electron microscopy, X-ray diffraction, Ultraviolet-visible spectroscopy, Fourier transform infrared spectroscopy, Raman spectroscopy, X-ray photoelectron spectroscopy, and Vibrating sample magnetometry. Room-temperature ferromagnetism with a maximum magnetization of up to 0.14 emu/g was discovered in the nanoparticles. The observed ferromagnetic ordering was related to the defect Ti-N-O structures at the interfaces between crystal phases. This suggestion is in good correlation with data obtained during spectroscopic studies. All the results demonstrate that the predominant role of the nitrogen and oxygen vacancies at the interfaces between titanium nitride, anatase, rutile, as well as the other mixed Ti-N-O phases contribute to the evolution of the room-temperature ferromagnetism. The maximum saturation magnetization of nanoparticles was extremely dependent on the N/O ratio, and area of peaks core-levels N 1s and O 1s. For the first time, an unknown phenomenonof a temporary “turn-off” effect of magnetization in hysteresis loops of some mixed-phase nanoparticles was discovered. The obtained results could be used in the search for new spintronic materials.