Evidence of collinear ferrimagnetism in (Fe, Tb)B metallic glasses from polarized beamneutron scattering

Abstract

The atomic-scale magnetic structures of two terbium-substituted(Fe0.83−xTbx)B0.17 metallic glasses have been determined by polarized beam neutron scattering measurementsusing the IN20 spectrometer at the Institut Laue-Langevin, Grenoble. The fourspin-dependent, neutron scattering cross-sections were measured in absolute units for thetwo glasses. The spin-flip cross-sections and were found to be small; they were independent of the scattering vectorQ, independent of the temperature and were also of the same magnitude as the nuclearincoherent cross-section, within experimental errors. These observations indicate that themagnetic structure in these glasses must be collinear. The non-spin-flip cross-sections werefound to have a hitherto unobserved shift of the first peak between the and channels. A (collinear) ferrimagnetic state which is consistent with the spin-flip cross-sections istherefore proposed for these glasses. The magnetic moments on the terbium atoms are alignedantiparallel to those on the iron atoms, and the values of both moments reduce to zero byx = 0.50 terbium, in agreement with magnetization data. A calculation of the non-spin-flipcross-sections based on this model correctly predicts the shift of the first peaks. Thisbehaviour arises because of the ferrimagnetic correlations between the magnetic momentsand the very strong magnetic scattering from the terbium atoms.