Yorihiko Tsunoda

Magnetic neutron scattering study of ordered Mn3Ir

Neutron-diffraction measurements were made on an ordered Mn3Ir single crystal in a wide temperature range up to 1030 K. The ordered Mn3Ir alloy was found to maintain an antiferromagnetic (AF) triangular spin structure up to the Neel temperature TN=960±10 K. The lattice parameter a shows a continuous change in the temperature range including TN. In contrast to the isostructural ordered Mn3Pt alloy, these observations indicate that an AF–AF phase transition is absent in the ordered Mn3Ir alloy.

Spin liquid state in ZnFe2O4

Abstract Magnetic diffuse scattering of neutrons was studied using a ZnFe 2 O 4 single crystal. Diffuse peaks are located along the lines of the first Brillouin zone boundary of fcc structure although the maximum peak intensity is observed at around (3/4 3/4 0). The results are compared with those for the 3D quantum spin liquid system Y(Sc)Mn 2 .

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.

Magnetic Properties of ZnFe2O4 as a 3-D Geometrical Spin Frustration System

Magnetic properties of ZnFe 2 O 4 were studied for various specimens prepared by different thermal and artificial treatments using neutron scattering, Mossbauer spectroscopy and DC and AC susceptibilities. We found a strong correlation between the magnetic Bragg peak intensity and the Mossbauer absorption line-width. Comparing with the susceptibility data, it is discussed what are the intrinsic magnetic properties of ZnFe 2 O 4 as a typical 3-D geometrical spin frustration system.

Spin fluctuations in an octahedral antiferromagnet Mn3Pt alloy

A new spin frustration system with an octahedral configuration of magnetic atoms was found. In neutron scattering measurements for an ordered Mn 3 Pt alloy, inelastic diffuse scattering intensity distributes along the first Brillouin zone-boundary of the fcc structure in the paramagnetic and the F-phases. Within the calculations based on a RPA, the experimental data in the paramagnetic phase are reproduced using antiferromagnetic couplings between the spins up to the third-neighbor exchange interactions. In the F-phase below the Neel temperature, a part of the Mn spins still fluctuates at the special site. The existence of the F-phase is a characteristic of the octahedral spin frustration system. The effects of the chemical disorder on the spin frustration are also studied using a specimen with a small atomic LRO parameter.

Phonons and Martensitic Transformation in Mn-rich γ-MnCu Alloys

The phonon dispersion relations in Mn-rich γ-MnCu alloys have been studied by means of neutron inelastic scattering. At the martensitic transformation, the [100] longitudinal phonon branch shows softening near the \( \varGamma \) point. In addition, the elastic constant C 12 is negative in a certain temperature range near the transition and the structural phase transition is caused by the vanishing of C 11 +2 C 12 . This mechanism of the martensitic transformation can successfully explain the peculiar properties of the γ-MnCu alloy system and the difference between this alloy and the γ-MnNi system. The tetragonal lattice deformation in the γ-MnCu alloy may be considered to be induced by the magnetic coupling force which accompanies the long-range magnetic order.

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)

The particle size effect of the spin-density wave in cubic γ-Fe precipitates in Cu

It is common knowledge that the magnetic structure of fcc Fe (γ-Fe) can be described by means of an incommensurate spin-density wave (SDW). Previous experimental data, however, were mostly obtained for γ-FeCo alloy precipitates in Cu in order to avoid the complexity of the structural phase transition. Since Fe is a fundamental element, reliable data on the SDW state for pure γ-Fe are highly desired. We present here neutron scattering data for the SDW in pure γ-Fe precipitates in Cu and discuss the particle size effect of the SDW.

Crossover of Spin Correlations in Pt100-XFeX (16 ≦X ≦25) Alloys

Magnetic structures of Pt 100- X Fe X ( X =16, 18, 24 and 25) alloys were studied by means of neutron elastic and inelastic scattering. Non-collinear antiferromagnetic structure is experimentally v...

Mössbauer Study on a Triangular Lattice Antiferromagnet LuFeCoO4

Mossbauer spectra of a single crystal of LuFeCoO 4 are studied in the temperature range between 4.2 K and 70 K. The Mossbauer spectra are separated into two components. We propose a model that one of three spins in a spin plane is parallel to the c -axis and other two orient to 120° to the c -axis. This model explains the experimental data satisfactory. It is concluded that the spins parallel to the c -axis are more stable than the other when temperature is increased. The Ising like character observed in susceptibility measurements can be explained by this spin arrangement in the spin planes.