Spin-glasslike behavior of K+-containing α-MnO2 nanotubes

Magnetic properties of K+-containing alpha-MnO2 nanotubes have been systematically investigated by dc magnetic measurements. Zero-field-cooled and field- cooled susceptibilities display divergences at low temperature, and a spin-glass temperature of 33.1 K is determined from the de Almedia-Thouless line by extrapolating the applied field to zero. The dc magnetic measurements, such as the field dependent magnetic susceptibility, hysteresis effect, thermoremanent magnetization, and memory effect, further confirm the spin-glass feature of the tetragonal alpha-MnO2 sample, which can be attributed to the geometrical frustration on the triangular lattices and the mixed valence of Mn3+ and Mn4+. (C) 2009 American Institute of Physics. [DOI: 10.1063/1.3117495]