Yutaka Nakai

Magnetic Structure of α-Mn

A neutron diffraction study has been made on single crystal specimens of α-Mn at 4.4°K, 60°K, and several other temperatures. Five types of magnetic form factor were in turn employed in the analysis. The magnetic structure is described by a single non-collinear configuration throughout the temperature range below T N with relatively large magnetic moments in Sites I, II and small moments in Sites III, IV, irrespective of which form factor is chosen. The experimental results seem to favor a localized moment model rather than a spin density wave model. When the analysis is based on the localized moment model, moments of 1.9, 1.7, 0.6 and 0.2 5 µ B may be assigned to Site I, II, III, and IV, respectively at 4.4°K, and the spin density in the atom is a superposition of a positive 3d-density and a negative 4s-density. The dependence of the effective exchange interaction coefficient on the inter-atomic distance is discussed.

The Crystal Structures of Magnesium Formate Dihydrate and Manganous Formate Dihydrate

Magnesium and manganous formate dihydrates crystallize in the space group P 2 1 / c , with the unit cell dimensions:

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.

Magnetic Moment Distribution in bcc Fe-Mn Alloys

It has been obtained by the experiments of diffuse scattering of neutrons that the magnetic moments of Fe and Mn atoms in α-FeMn alloys are 2.23±0.01 and 0.7±0.25µ B at 0 K, respectively. the magnetic moment of Fe agrees with the theoretical value obtained by CPA calculation, while that of Mn is smaller than the theoretical one. The spatial fluctuation of the magnetic moment of Fe and Mn atoms cannot be observed within the experimental accuracy. The temperature dependence of the magnetic moments of Fe and Mn has been studied, and we have found an anomalous behavior in . This behavior cannot be explained by the molecular field theory proposed by Jaccarino et al.

Third Harmonics of Spin Density Wave in Cr and Its Alloys

The third harmonics of the spin density wave in pure Cr, CrMn and CrV alloys were studied by means of neutron diffraction, and the following results were obtained. The phase relation between the third and the primary spin density wave was determined to be “rectangular like” in pure Cr and in CrMn alloy. The ratio of the amplitude of the third harmonics spin density wave to that of the primary spin density wave, | S 3 / S 1 |, increases in CrMn and decreases in CrV alloys compared with that of the pure Cr. These results can be qualitatively explained by both of the theories based on the two band nesting model and the virtual bound state approach to the spin density wave.

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.

Preparation of α‐Manganese Single Crystals and Their Physical Properties

Single crystals of α‐manganese were grown by the distillation method. These weigh about 300 mg. Crystallographic parameters which define the positions of manganese atoms have been determined by x‐ray diffraction. The magnetic structure was determined with better accuracy than that determined by the powder method. It is concluded that the collinear model cannot explain the experimental data very well and therefore a noncollinear model is proposed, in which the magnetic moments in sites I and II are much larger than those in sites III and IV.

Internal Field Distribution in Au (Fe) Spin Glass System and Stable Distribution

The internal field distribution for a Au 0.97 Fe 0.03 spin-glass system is obtained from the Mossbauer absorption experiment using a relation between a hyperfine field and an internal field, which holds in the case of RKKY interaction. The obtained distribution is well explained with the stable distribution with the characteristic index α of 0.86. It is shown that the internal field distribution is close to Lorentzian but far from Gaussian distribution.

Phase relation between SDW and strain wave in chromium

Abstract The phase relation between SDW and strain wave in Cr has been studied by neutron diffraction and analysed on the basis of the rigid spin model. The intensity ratio between two satellites (1 ± δ 0 0) has been determined from observed results as 1.044, after making corrections mainly due to the magnetic form factor and the Lorentz factor. This result can be understood by a model that the largest elongation of the lattice spacing appears at atoms having the maximum spin magnetic moment.

Neutron Diffraction and Mössbauer Spectroscopic Studies of β-Mn(Sn) Alloys

About 90% of Sn atoms in β-Mn structure are found by means of neutron diffraction to occupy site II and neither antiferromagnetic long range order nor remarkable short range order was observable. By Mossbauer spectroscopy of 119m Sn, the magnitude of the electric field gradient (EFG) decreases with an increase in Sn concentration. The EFG distribution functions are expressed by the sum of two Lorentz distributions. From the stable distribution analysis of internal field distributions, it becomes clear that the magnetic moments randomly freeze in the noncollinear manner.