High-temperature ferromagnetism of Li-doped vanadium oxide nanotubes

• Published in: Europhysics letters Vol. 88; no. 5; pp. 57002 - 57006
• Main Authors: Popa, A. I, Vavilova, E, Arango, Y. C, Kataev, V, Täschner, C, Klauss, H.-H, Maeter, H, Luetkens, H, Büchner, B, Klingeler, R
• Format: Journal Article
• Language: English
• Published: IOP Publishing 01.12.2009; EDP Sciences
• Subjects: 73.22.-f; 75.20.-g; 75.75.+a
• ISSN: 0295-5075; 1286-4854
• DOI: 10.1209/0295-5075/88/57002

The nature of a puzzling high-temperature ferromagnetism of doped mixed-valent vanadium oxide nanotubes reported earlier by Krusin-Elbaum et al., Nature, 431 (2004) 672, has been addressed by static magnetization, muon spin relaxation, nuclear magnetic and electron spin resonance spectroscopy techniques. A precise control of the charge doping was achieved by electrochemical Li intercalation. We find that it provides excess electrons, thereby increasing the number of interacting magnetic vanadium sites, and, at a certain doping level, yields a ferromagnetic-like response persisting up to room temperature. Thus we confirm the surprising previous results on the samples prepared by a completely different intercalation method. Moreover our spectroscopic data provide first ample evidence for the bulk nature of the effect. In particular, they enable a conclusion that the Li nucleates superparamagnetic nanosize spin clusters around the intercalation site which are responsible for the unusual high-temperature ferromagnetism of vanadium oxide nanotubes.