Yasunori Tanji

Lattice Distortion and Elastic Properties of Antiferromagnetic γ Mn-Ni Alloys

Lattice parameters and elastic moduli of polycrystalline γ Mn alloys containing 12–40 at% Ni have been measured in a temperature range between –180° and 250°C. The face-centred cubic lattice undergoes a tetragonal distortion, either c / a 1, or an orthorhombic distortion at low temperatures. Both Youngs modulus and shear modulus exhibit a step-type change at the Neel point and a broad minimum near the transition temperature of lattice distortion. The elastic behaviour is discussed on the basis of the so-called Δ E effect due to the displacement of antiferromagnetic domain walls. This effect may possibly be enhanced by the lattice softening in the γ Mn–Ni alloys.

Debye Temperature and Lattice Deviation of Fe-Ni (fcc) Alloys

Debye temperature \(\varTheta_{\text{M}}\) and maximum lattice deviation \(\sqrt{\overline{U^{2}}}\) of Fe-Ni( fcc ) alloys are calculated in the range of 0°∼500°C using the values of Youngs modulus and shear modulus previously obtained with the same specimens. The results obtained are the following: (1) In its concentration dependence, Debye temperature at the paramagnetic state \(\varTheta_{\text{Mp}}\) shows a minimum at around 40% of Ni. (2) In its concentration dependence \(\sqrt{\overline{U^{2}}}\) shows a maximum at around 40% of Ni. As T becomes higher, the concentration showing \(\sqrt{\overline{U^{2}}}\) maximum gradually moves toward the Fe-rich side. (3) The concentration dependence of resistivity at the paramagnetic state ρ p does not follow Nordheims rule. As one of the significant factors causing this “shift” from the rule, the contribution of thermal agitation of lattice cannot be neglected.

Circular magnetic X-ray dichroism at the K-absorption edge in Fe-Ni alloys

The first systematic measurements of circular magnetic X-ray dichroism (CMXD) effects at the K -edge in 3 d -transition metal alloys have been made in Fe–Ni alloy over a wide composition range. It has been found that the CMXD spectrum at the Fe K -edge is similar to that at the Ni K -edge in each alloy, indicating that the CMXD spectra at the K -edge mainly reflect an itinerant character of 4 p -states. The features of the CMXD spectra correspond to those of X-ray absorption near-edge structure (XANES) spectra, reflecting the change of crystal structure. The signal intensities around the absorption edge energy, E 0 , have strong Ni concentration dependence, suggesting a close relationship between the CMXD effects around E 0 and the spin polarization of 3 d -states.