Incommensurate magnetic structure of β-MnO2 -: art. no. 172401

beta-MnO2 has a well-known screw type magnetic structure. According to Yoshimori [J. Phys. Soc. Jpn. 14, 807 (1959)] the pitch of this screw is exactly 7/2c. We performed neutron powder diffraction measurements which show that the pitch of the screw is about 4% shorter than <7/2c so beta-MnO2 has an incommensurate magnetic ordering. This result has important consequences on the calculation of the values of the exchange integrals in beta-MnO2 by Yoshimori, and Ohama and Hamaguchi [J. Phys. Soc. Jpn. 30, 1311 (1971)]. The present results are compared with the neutron powder diffraction data measured on beta-MnO2 by Gonzalo and Cox [An. Fis. 66, 407 (1970)] and recent magnetic x-ray diffraction by Sato [J. Phys. Soc. Jpn. 70, 37 (2001)]. The values of the magnetic moments of Mn+4 ions are estimated.