phases in Ni-Al alloys with L1o ↔ B2 thermoelastic martensitic transformation has been studied by X-ray analysis. Ni 5 Al 3 can form from both the L1o and B2 structures, but the kinetics of L1o → Ni 5 Al 3 and B2 → Ni 5 Al 3 reactions are significantly different. A homogeneous mechanism for the former reaction and a mechanism of precipitation and growth for the latter are proposed. Ni 2 Al forms from the B2 structure by the complex rearrangement of atoms. The initial stage of this reaction proceeds very rapidly and involves segregation of Ni atoms into Ni-rich zones leading to a Ni depletion in the surrounding regions. The nucleation of Ni 2 Al retards the Ni 5 Al 3 formation, so preaging in the B2 region affects the kinetics of the L1o → Ni 5 Al 3 reaction on further aging in the L1o region. The microstructural mechanism for this effect is suggested.

Magnetic and crystalline structure as well as magnetic and damping properties of binary iron-aluminum (Fe-Al) alloys in the region from 3 to 12 wt.% aluminum have been investigated by using transmission electron microscopy (TEM), X-ray scattering, neutron scattering, magnetic hysteresis loops, and magnetostriction studies. It was found that independent of the impurity content (vacuum or air melting of alloys) the concentration dependence of damping capacity displays a pronounced maximum in the region of ̃5.5 wt.% aluminum, where the maximum value of the logarithmic decrement δ exceeds 25%. It was found that the magnetic domain structures in the bulk materials differ strongly for the alloys in the high damping state and for the alloys with the same composition after suppressing the high damping by heat treatment. The analysis of obtained magnetic data and microstructural analysis shows that the necessary condition for the appearance of the high damping state is the formation of a special magnetic domain structure with an enhanced fraction of movable 90-deg domain walls. An additional condition is the formation of a crystalline structure which provides a moderate value of magnetic hysteresis losses and coercive force. For the Fe-Al alloys investigated, it means that the most favorable structural condition for high δ-values is an intermediate stage of short-range ordering of the D03 structure.

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A systematic study of temperature dependence of magnetic inelastic neutron scattering for itinerant antiferromagnet Mn(12%Ge) is presented. At low temperatures the experimental data are well described in terms of damped spin waves. This description becomes insufficient at least 150 K below TN. In the temperature range 200-400 K the integrated intensity of distribution for energy transfer 13 THz increases by one third and the shape of the deconvoluted neutron scattering cross-section changes. These changes suggest that ca. 200 K below TN an additional contribution to the inelastic neutron scattering starts to appear and that its origin is different from spin waves.PACS numbers: 75.30.Ds, 75.50.EeThe magnetic excitations in itinerant antiferromagnets are not yet satisfactorily understood. In particular more detailed studies of their temperature dependence are needed. The aim of our experiment was to study the evolution of the neutron scattering by spin waves at low temperature into the paramagnetic scattering above TN.The crystal structure of the γ-Mn alloys with high: manganese concentration (fcc in the paramagnetic phase) becomes tetragonal with c < a in the antiferromagnetic (AF) phase. Many alloys with lower manganese concentration remain fcc in the AF phase. In some narrow concentration region (different for different diluents) two other crystal structures: orthorhombic and tetragonal with c > a appear in the AF phase. The composition of the investigated alloy is close to the composition for the tricritical point for paramagnetic fcc, AF tetragonal and AF (483)