mu SR study of YMn12

The Mn ions occupy three different sites (8i, 8j, 8f) in equal population i n YMn12, which has the tetragonal ThMn12 structure with space group I4/mmm. They possess a different magnetic moment at the 8f site (0. 14 mu(B)) comp ared to the 8i and 8j sites (0.42 mu(B)). The compound orders antiferromagn etically with T-N approximate to 100 K. Above T-N the muon-spin relaxation is dominated by the nuclear dipole fields of Mn-55. The influence of the el ectronic moments on Mn is only weakly felt near T-N when critical slowing d own occurs. Below T-N, no spontaneous spin precession is observed and the z ero-field spectra can be described by a Lorentzian Kubo-Toyabe pattern. Thi s shows that the muon must occupy an interstitial site where all contributi ons to the local field cancel for the antiferromagnetic spin structure. Lon gitudinal field measurements demonstrate that the spectra are essentially s tatic in nature. It is remarkable that the different Mn sites with their di fferent Mn moments do not show in the mu SR spectra. The likely muon stoppi ng sites are discussed. (C) 2000 Published by Elsevier Science B.V. All rig hts reserved.