Defect types and room-temperature ferromagnetism in undoped rutile TiO₂single crystals

Abstract

Room-temperature ferromagnetism has been experimentally observed in annealed rutile TiO2 single crystals when a magnetic field is applied parallel to the sample plane. By combining X-ray absorption near the edge structure spectrum and positron annihilation lifetime spectroscopy, Ti3+—VO defect complexes (or clusters) have been identified in annealed crystals at a high vacuum. We elucidate that the unpaired 3d electrons in Ti3+ ions provide the observed room-temperature ferromagnetism. In addition, excess oxygen ions in the TiO2 lattice could induce a number of Ti vacancies which obviously increase magnetic moments.

The Use of Ultra-Small Fe3O4 Magnetic Nanoparticles for Hydrothermal Synthesis of Fe3+-Doped Titanate Nanotubes

“…Since the discovery of room temperature ferromagnetism in Co-doped TiO 2 thin films [ 63 ] understanding the causes of ferromagnetism in TiO 2 materials is a subject of lively discussion [ 64 , 65 , 66 , 67 , 68 , 69 ]. The hysteresis loop diagram for S1 resembles the results obtained in paper [ 70 ] for TiO 2 single crystals annealed in a high vacuum where the investigated samples were diamagnetic at room temperature with a characteristic low-field ferromagnetic behavior. In paper [ 70 ], it was concluded that the unpaired 3d electrons in Ti 3+ ions can be responsible for the observed room temperature ferromagnetism.…”

“…The hysteresis loop diagram for S1 resembles the results obtained in paper [ 70 ] for TiO 2 single crystals annealed in a high vacuum where the investigated samples were diamagnetic at room temperature with a characteristic low-field ferromagnetic behavior. In paper [ 70 ], it was concluded that the unpaired 3d electrons in Ti 3+ ions can be responsible for the observed room temperature ferromagnetism. In sample S1, a similar mechanism can explain its ferromagnetic properties at a weak magnetic field.…”

Titanium 3d ferromagnetism with perpendicular anisotropy in defective anatase

“…This work presents a way to produce a magnetic layer at the surface of TiO 2 anatase by low-energy Ar + -ion irradiation [65]. Defect-induced magnetism in TiO 2 has been studied in the past [7,[66][67][68][69][70], achieving Curie temperatures of up to 880 K [10,69]. The main difference between our approach and those published is related to the low ion energy and fluences we use, which allow us to produce a robust magnetic layer close to the surface of the films.…”

Function ofTiO2Lattice Defects toward Photocatalytic Processes: View of Electronic Driven Force

“…Here a hypothesis is made that such heat do not or has little influence on the separation and migration of charge carriers. [64] and it could be seen that the potential field of the neighbouring Ti is The atomic lattice is blurred Maybe exists [72,123] Ultraviolet-visible spectroscopy (UV-vis) An optical absorption band above 400 nm Maybe exists [30] Photoemission spectroscopy (PL) The emission position and intensity Type, relative concentration of defects [124] Raman spectroscopy Variation in vibration of O and Ti-related region Type of defects [30,38,72] X-ray photoelectron spectroscopy (XPS) Valence state variation Type of defects mainly Ti 3+ [30,37,72,89] Electron paramagnetic resonance (EPR) factor calculated from the position of the sharp signal Type of paramagnetic defects [35,123,125,126] Positron annihilation lifetime spectroscopy (PALS) The lifetime of the positrons Size, type, and relative concentration of defects [68] Scanning tunneling microscopy (STM) Light dot in pictures The type, position of defects [31,113,120] Atomic force microscopy (AFM) Comparison of pictures The type, position of defects [38] Temperature programmed deoxidation (TPD) A narrow peak related to partial oxygen loss according to temperature. the most influenced site whereas the variations die largely in distance.…”

“…Considering the oxygen activity and temperature, surface treatment methods (e.g., annealing in vacuum condition [68], thermal treatment under reducing atmosphere (H 2 , CO, NO), and bombardment using electron beam [69,70], neutron, or -ray) are introduced to obtain defective surfaces. The bulk ODTs can be directly obtained from sputtering method without further modifications on the TiO 2 samples.…”