NUCLEAR AND MAGNETIC MEDIUM-RANGE ORDER IN TBXSI1-X AMORPHOUS-ALLOYS (X = 0.59, 0.87) CONTAINING HYDROGEN

Small-angle neutron scattering measurements were carried out on (Tb0.59Si0.41)Ho.15 and (Tb0.87Si0.13)H0.15 amorphous alloys above and below the magnetic ordering temperature for zero field cooled (ZFC) and field cooled (FC) samples. From the measurements we have determined the spatial variation of the nuclear and magnetic scattering length per unit volume and describe the nuclear and magnetic medium-range order (MRO) for ZFC and FC samples. The existence of large nuclear and magnetic domains (or of nuclear and magnetic fluctuations) extending over a few hundred Angstroms coexisting with less extended (a few tens of Angstroms) fluctuations is shown. Moreover some small nuclear or magnetic inhomogeneities are found to exist and they seem to contain most of the 15 atomic per cent of hydrogen which have been detected in our sample composition. An applied magnetic field tends to align the local magnetization, but does not increase the spatial extension of fluctuations or domains, locked by the nuclear MRO, although their contrast is found to decrease. The comparison with the amorphous alloy Tb65Cu35 shows the generality of these results but does not allow us to understand the difference in the macroscopic magnetic properties, in particular the difference between the hysteresis loops.