Y. Tsunoda

Strain wave in pure chromium

Abstract New satellites were observed in a single crystal of pure chromium below the Neel point by X-ray diffraction at the positions apart by 2 δ from the Bragg points. The observed anisotropy of the satellite intensity around the Bragg point and the temperature dependence of 2 δ yield the conclusion that the lattice spacing in the direction of the wave vector of the spin density wave are modulated periodically and that the period is a half of that of the SDW. The experimental results coincide with the prediction made by a theory of the exchange striction in transition metal alloys.

Anomalous lattice contraction and magnetism of γ-Fe precipitates in Cu

The lattice parameter of FCC ( gamma -)Fe precipitates in a Cu matrix is investigated as a function of the size of the precipitates. With prolonged aging, noncoherent gamma -Fe precipitates with about 0.2% smaller lattice spacings than the coherent ones are found. The structural phase transition, the magnetic structure and the Neel temperature of this new state are studied using X-ray and neutron diffraction methods. Antiferromagnetic ordering takes place accompanying a structural phase transition as in the coherent state. The observed Neel temperature is slightly higher than the previously reported value TN=67 K. Various magnetic properties of gamma -Fe precipitates in Cu are discussed on the basis of the present experimental data.

Structural phase transition of γ-Fe precipitates in Cu

The structural phase transition of gamma -Fe precipitates in a Cu matrix is studied using the X-ray diffraction technique. At low temperature, the FCC lattice uniformly contracts along the c axis by 0.17%. In the c plane the mean value of the lattice spacing expands by 0.19%, but the atomic positions are modulated by a sinusoidal wave propagating along the (110) direction with the (110) polarisation vector. Various properties of the periodic lattice wave (PLW) are studied. The wavelength and amplitude of the PLW depend on the size of the precipitates. The origins of the PLW and the size effects are discussed.

Magnetic structure of γ-Fe precipitates in a Cu matrix

The recent discovery of a periodic distortion of the lattice structure of gamma -Fe precipitates in Cu motivated the authors to re-examine the magnetic structure of these precipitates using a neutron diffraction technique. They find that the spin structure is that of a longitudinal type-1 antiferromagnet as is well known but the spins are within a c plane and modulated in space with a wavevector Q which is the same as that of the displacement wave of the lattice. Several features of the spin structure are discussed.

Strain wave in Cr rich CrFe alloys

Abstract Satellite reflections due to the strain wave were observed in Cr rich Crue5f8Fe alloys by X-ray diffraction. The magnitude of the wave number vector of the strain wave decreases whenever the temperature approaches the ISDW-CSDW transition. From the temperature and concentration dependences of the strain wave and the lattice parameter observed by X-ray diffraction the magnetic phase diagram of Crue5f8Fe was determined.

Magnetic excitation in CuMn spin glass alloy

The spin dynamics of a spin glass alloy Cu78.7Mn21.3 have been studied by neutron inelastic scattering. Measurements have been made at 20, 150, and 290 K by the constant E mode of operation. Magnetic excitations with rather large energy transfer have been observed around the (1u2009 1/2 u20090) and the (1u2009 1/2 ±δu20090) magnetic diffuse peak positions above and below the spin freezing temperature (Tf∼90 K). The results indicate the existence of strong space and time correlations of the spins over the temperature range of the measurements. The experimental data are well explained by a model of dynamically fluctuating spin clusters with a broad distribution of relaxation times.

Elastic Moduli of γ-MnCu Alloys

The temperature dependence of elastic moduli has been measured for γ-MnCu alloys with Mn contents of 40, 70, 80 and 85 at.% by means of ultrasonics. In contrast to the Invar alloys, softening of C 11 and C (=1/2(C 11 -C 12 )) is observed at the paramagnetic region and C 11 , C 44 and C show stiffening below T N . Apart from the elastic anomaly associated with the martensitic transformation, a drastic decrease of bulk modulus with the increase of Mn content is observed for the wide concentration range of γ-MnCu system.

Elastic anomalies of γ-Fe precipitated in Cu

Abstract The elastic moduli of γ-Fe precipitates in Cu matrix have been measured by ultrasonic method. The elastic moduli C 11 and C′ show distinct anomalies associated with fcc-fct martensitic transformation which takes place at the onset of the antiferromagnetic order. The similarities of γ-Fe and γ-MnCu alloys not only in the magnetic structure but also in the elastic properties are emphasized.

Inclined spin axis of Mn-rich γ-MnCu alloy

Abstract An existence of (0 0 1) magnetic elastic peak was confirmed by a neutron diffraction study of Mn-rich γ-MnCu alloy single crystals, which indicates that the magnetic moments of γ-MnCu alloys are also inclined from the c-axis as well as those of γ-Fe and γ-Fe alloys.

Phonon modes in mass-defect disordered alloy NiPt

Abstract The phonon dispersion relations of 00σT branch were measured for Ni95Pt5 and Ni70Pt30. The dispersion curves breaks up into two branches. Th general shape and its concentration dependence can be explained qualitatively by Taylors coherent potential approximation theory.