Nobuhiko Kunitomi

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.

Antiferromagnetism in disordered B.C.C. Cr-Mn Alloys

The neutron diffraction, electrical resistivity and magnetic susceptibility measurements on b.c.c. Cr-Mn alloys containing manganese from 7.0 to 25.3 atomic percent have shown that the alloys are antiferromagnetic but disordered atomically. The obtained results are shown to be compatible with the theoretical conclusions from the spin density wave model.

Experimental Test of Rigid Band Models for Cr by Means of Cr-V-Mn Ternary Dilute Alloys

Electrical resistivity and powder neutron diffraction patterns for Cr-V-Mn ternary dilute alloys have been measured at various temperatures. From the measurement an estimation is made on the Neel temperature, spin arrangement, average magnetic moment and wave vector of spin density wave. The ternary data are compared with those already obtained on the Cr-V or Cr-Mn binary dilute alloys. This comparison is made on the same scale of effective concentration, i.e. the manganese concentration subtracted by the vanadium concentration in units of atomic percent. The results have shown that there is a good agreement between the data on the ternary and binary alloys. This fact supports the validity of rigid band approximation. The wave vector was evaluated using the three models which were proposed for explanation of the properties of chromium metal. The results were compared with the experimental results.

Neutron Diffraction Study on Chromium Alloy with Small Amounts of Vanadium

A neutron diffraction study has been performed on chromium alloy cantaining 0.45 atomic percent vanadium in comparison with the existing results on pure chromium. An experimental evidence has been obtained that both the magnetic period and magnetic moment decrease rapidly with increasing vanadium concentration supporting the theoretical prediction by Tachiki and Nagamiya. The implications of the experimental details are discussed in terms of the spin density wave mechanism.

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.

On the Neutron Diffraction Study of FeGe

A powder neutron diffraction study has been made of FeGe. Published neutron diffraction data do not show any antiferromagnetic diffraction lines, while Mossbauer effect measurements do show that this substance is an antiferromagnetic with a Neel temperature at 400°K. The present study has revealed the presence of (10\(\frac{1}{2}\)) line, which is consistent with the Mossbauer data. The Fe spins on a c -plane are coupled ferromagnetically and directed along the c -axis, while they are coupled antiparallel to those on next Fe-containg c -planes.

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.

Ferromagnetism of the Intermetallic Compound UFe2

The magnetic properties of UFe/sub 2/ were investigated at 300 deg K to 100 deg K. Metallic uranium and electrolytic iron, each 99.9% pure, were melted together in a vacuum and held at 1300 deg C for one hour, after which they were cooled to room temperature. Further cooling revealed evidence of ferromagnetism at 195 deg K. (L.N.N.)

Neutron Scattering Measurements in Chromium near the Néel Temperature

Yorihiko Tsunoda, Yoshikazu Hamaguchi, Nobuhiko Kunitomi, Neutron Scattering Measurements in Chromium near the Neel Temperature, J. Phys. Soc. Jpn. 32, pp. 394-399 (1972)

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.