F. Hippert

Magnetic order and canting in a reentrant alloy studied by magnetization, mössbauer and neutron scattering

Abstract Inelastic neutron scattering and Mossbauer measurements have been carried out on the reentrant alloy (Fe0.765Mn0.235)75P16B6Al3, using samples from the same ribbon. The canting temperature deduced from Mossbauer data coincides with the appearance of a central peak in the inelastic neutron scattering. Polarized neutron transmission experiments are consistent with a ferromagnetic domain-like structure at all temperatures below the Curie point.

Magnetic defects observed by small angle neutron scattering in applied magnetic fields in a weakly frustrated system

Abstract Small angle neutron diffraction measurements have been performed on a “reentrant” polycrystalline Ni 1- x Mn x alloy as a function of temperature and applied magnetic field. In applied fields, the scattering I ( q ) exhibits a peak which moves towards higher value as the field increases, while the total intensity strongly decreases. All these variations take place at nearly constant magnetization. The magnetic scattering I ( q ) obtained for different field values is shown to obey an approximate scaling law. These results can be interpreted in terms of the existence of rather well defined clusters (magnetic defects). Within this model, these experiments provide the observation of the variation of their size and density with field and temperature. Finally, very similar observations have been made for amorphous (FeMn) 75 P 16 B 6 Al 3 .

Origin of magnetism in Al–Mn and Al–Pd–Mn quasicrystals, related crystals and liquids

Abstract Whereas most of crystalline Al(Si)–Mn and Al(Si)–Pd–Mn phases are non-magnetic, measurements show the existence of localized magnetic moments on a small fraction of the Mn atoms in quasicrystals and in a few crystalline approximants. We develop a new model that shows that an indirect Mn–Mn interaction via the conduction band is determinant for the existence or not of a magnetic moment, even when Mn–Mn distance is 5 A or more. These models allow us to understand experimental measurements.

Spin waves in the low temperature phase of the “reentrant” (Fe0.77Mn0.23)75 P16B6AI3

Inelastic neutron scattering studies in a “reentrant” (Fe 1- x Mn) 75 P 16 B 6 Al 3 amorphous alloy reveal a series of anomalies in the temperature evolution of the spin wave spectrum, almost identical to those previously reported in a Ni 1- x Mn x reentrant alloy. As the temperature decreases below to, we observe first an increase of the damping and a decrease of the stiffness constant then, at still lower temperature a reversed evolution i.e. an increase of the stiffness and a decrease of the spin wave linewidth at small q . The same anomalies persist under a moderate applied field (1.5 kG). Therefrom this behaviour appears to be an intrinsic property of the reentrant alloy. It emphasizes the influence of dynamical processes on the low temperature properties of these systems.

Small angle neutron scattering in reentrant spin glasses

Abstract Neutron scattering measurements at very low q values were performed in reentrant spin glasses (Fe1−xMnx)75P16B6Al3 and Au1−xFex. By fitting the data with a phenomenological law A (q 2 + K 2 ) α we show that the exponent α varies continuously with the temperature. The data are discussed in relation to the scattering from a dilute non-frustrated ferromagnet and neutron depolarisation experiments.