Department of Radiological Sciences, University of California, Irvine, Irvine, CA 92697, USA.
Nanotechnology. 2013 Jul 12;24(27):275704. doi: 10.1088/0957-4484/24/27/275704. Epub 2013 Jun 14.
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 6×10(17), 3×10(16), and 3 × 10(15) 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 T(C) ~ 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 Ti(3+) 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.
通过超导量子干涉仪（SQUID）和电子自旋共振（ESR）方法，在 1.8-300 K 的温度范围内，研究了电化学阳极氧化生长的未掺杂锐钛矿、金红石和无定形二氧化钛（TiO2）纳米管的磁性。当测试的磁性中心浓度分别为 6×10(17)、3×10(16)和 3×10(15)cm(-3)时，所有锐钛矿、金红石和无定形 TiO2 纳米管在整个温度范围内都表现出顺磁行为。TiO2 纳米管的直径从 40-160nm 不等，对观察到的磁性没有显著影响。SQUID 数据显示，在低温下，锐钛矿的 M-H 关系具有很强的非线性，Arrot 图分析表明，该样品具有约 6K 的居里温度 T(C)的铁磁性。然而，ESR 研究没有显示出长程磁有序的证据。ESR 研究揭示了两个 g1 = 1.928 和 g2 = 2.028 的磁性中心，它们存在于所有样品中。g1 = 1.922 的共振峰归因于氧空位导致的 Ti(3+)阳离子中心，而 g2 = 2.028 的共振峰归因于表面吸附剂。无定形样品的 ESR 光谱包含了额外的共振峰，相应的 g 值为 2.228、1.873 和 1.715，这可能是由于这些样品的无序性质所致。
