Origin of magnetism in undoped TiO2 nanotubes

• Published in: Nanotechnology 2013-07, Vol.24 (27), p.275704-275704
• Main Authors: Alivov, Yahya, Grant, Ted, Capan, Cigdem, Iwamoto, W, Pagliuso, P G, Molloi, Sabee
• Format: Article
• Language: English
• Subjects: Applied sciences; Condensed matter: electronic structure, electrical, magnetic, and optical properties; Cross-disciplinary physics: materials science; rheology; Electronics; Exact sciences and technology; Magnetic properties and materials; Magnetic properties of nanostructures; Materials science; Methods of nanofabrication; Molecular electronics, nanoelectronics; Nanoscale materials and structures: fabrication and characterization; Nanotubes; Physics; Semiconductor electronics. Microelectronics. Optoelectronics. Solid state devices
• ISSN: 0957-4484; 1361-6528
• DOI: 10.1088/0957-4484/24/27/275704

Magnetic properties of undoped anatase, rutile, and amorphous titanium dioxide (TiO2) nanotubes grown by electrochemical anodization were studied by superconducting quantum interference device (SQUID) and electron spin resonance (ESR) methods in the temperature range 1.8-300 K. All anatase, rutile, and amorphous TiO2 nanotubes were found to exhibit paramagnetic behaviors in the entire temperature range when tested with magnetic center concentrations of 6×1017, 3×1016, and 3 × 1015 cm−3, respectively. The diameter of the TiO2 nanotubes varied from 40-160 nm and has no significant effect on the magnetic properties observed. SQUID data showed strong nonlinear M-H relationships for anatase at low temperatures, and Arrot plot analysis suggested ferromagnetism in the sample with a Curie temperature TC ∼ 6 K. However, ESR studies showed no evidence for long-distance magnetic ordering. ESR studies revealed two magnetic centers with g1 = 1.928 and g2 = 2.028 that were common to all samples. The resonance peak at g1 = 1.922 was ascribed to Ti3+ cations centers resulting from oxygen vacancies, while the peak at g2 = 2.028 was ascribed to surface absorbents. The amorphous sample ESR spectrum contained additional resonance peaks with corresponding g values at 2.228, 1.873, and 1.715 that possibly resulted from the disordered nature of these samples.