N. Kunitomi

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.

High-Pressure Cell for Neutron Scattering

We have developed a high-pressure cell for neutron scattering. The cell uses a barrel-shaped support cylinder made of sintered ceramics. Samples 6 mm in diameter and 10 mm long can be accommodated. The cell is suitable for use at low and high temperatures, after a pressure generated at room temperature is locked. The change of pressure on cooling to cryogenic temperatures is estimated by measuring the lattice parameter of NaCl. Besides the pressure locking technique, continuous pressurization can be achieved at room temperature by using a built-in mini-press while the cell is mounted on a goniometer of neutron spectrometer.

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.

Neutron diffraction study on the hyperfine-enhanced nuclear spin order of HoVO4☆

Abstract A neutron diffraction experiment on the hyperfine enhanced nuclear spin system of HoVO4 has been carried out following adiabatic demagnetization cooling. Below 4.5 mK we observed magnetic diffraction peaks due to antiferromagnetic order of the hyperfine enhanced nuclear spin system. A spin-flop transition in an applied magnetic field of about 80 Oe was also observed. The neutron diffraction results are consistent with the magnetic structural model proposed by Bleaney on the basis of dipolar energy considerations.

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 CrFe 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 CrFe was determined.

Diffusion of Cadmium into Single Crystals of Copper

The diffusivity of cadmium into single crystals of copper has been measured in the temperature range from 725°C to 950°C using radioactive isotope Cd 115 as a tracer. The results indicate that D 0 =0.935 cm 2 /sec and H =45,700 cal/mol. These values are compared with the corresponding values for the diffusion of zinc into copper in order to investigate the effect of the difference in atomic radii.

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 (1  1/2  0) and the (1  1/2 ±δ 0) 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 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.