Published online by Cambridge University Press: 10 February 2011
A comprehensive study of transport properties and magnetism on β-MnO2 reveals the strong coupling between the conduction electrons and the localized spins which are supposed to form a magnetic helix below TN ∼ 92 K. We also show the direct evidences of the helical magnetism by means of the measurements of the anisotropy in the magnetic susceptibility and the observation of x ray magnetic scatterings on a single crystal of β-MnO2. These results are consistent with proper-type helix model proposed by Yoshimori [J. Phys. Soc. Jpn. 14, p. 807 (1959)]. This model also qualitatively agrees with the anisotropy in magnetoresistance that appears below TN. The pitch of the magnetic helix is not commensurate to the lattice and it is slightly temperature dependent. The intensity of several Bragg peaks drastically changes at TN suggesting that the magnetic ordering is accompanied by a lattice distortion.