Room-temperature ferromagnetism evolution in nanostructured titanium nitride superconductors—the influence of structural defects

Abstract

Titanium nitride (TiN) nanoparticles were obtained by calcining nanotubular titanic acid (NTA) in flowing ammonia. The morphology, crystal structure, and chemical features of as-prepared products were investigated by means of transmission electron microscopy, energy-dispersive X-ray spectrometry, X-ray diffraction, and Raman spectrometry. In the meantime, their magnetic properties were examined using a superconducting quantum interference device. Surprisingly, it was found that as-prepared TiN nanoparticles experienced a gradual diamagnetic to ferromagnetic transition at room temperature with extending nitridation time, accompanied by a noticeable shift of X-ray diffraction peaks towards lower 2θ therewith. More importantly, the magnetic properties of as-prepared TiN nanoparticles can be manipulated not only by adjusting nitridation time but also by doping non-magnetic elements during the calcining process. We speculate that the observed magnetic properties of the as-synthesized products without any magnetic impurities may be attributed to their structural defects, and there is an inner relationship between their composition and magnetic properties. As an initial study to probe the inner relationship between the composition features and magnetic properties of nanostructured dilute magnetic nitrides, this study, we believe, provides a rare example of a room-temperature magnetic transition of a superconductor and could help in acquiring insights into the origin of ferromagnetism in a broad range of non-magnetic nanostructures.