An X-ray diffraction study reveals that an introduction of a small amount of Co suppresses the structural phase transition of gamma -Fe precipitates in Cu and the cubic gamma -FeCo alloy precipitates are available even at the lowest temperature. The magnetic structure of the cubic gamma -Fe100-xCox (x<4) alloy precipitates is studied by neutron diffraction, and spin-density wave (SDW) propagating along the cubic axis is found for these specimens. The Neel temperature and wavelength of the SDW decrease with increasing Co concentration. It is demonstrated that the magnetic structure of the cubic gamma -Fe precipitates is also the SDW state.

Single crystals of ZnFe 2 O 4 are investigated with neutron scattering measurements from the viewpoint of geometrical frustration. Magnetic diffuse scattering was distributed along the first Brillouin zone boundary of the fcc structure. The results show that the frustration occurs between the antiferromagnetically coupled third-neighbor spins, rather than between the similarly coupled first-neighbor spins. In addition, another type of diffuse scattering was found around some nuclear Bragg peak positions. This indicates that the first-neighbor exchange interaction in the 90°configuration is ferromagnetic rather than antiferromagnetic. Energy spectra were investigated at several points. The unusual magnetic behavior originates from the geometrical frustration and a unique property of the first-neighbor interaction.

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 Néel 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.

X-ray diffraction, neutron diffraction, and susceptibility measurements were performed on 7 LiMn 2 O 4 powder specimen. The Jahn-Teller lattice distortion induces a phase transition from cubic to orthorhombic structure at Tϭ283.5 K on cooling. A series of well-defined magnetic Bragg peaks appears below T N ϭ65 K. A complete charge ordering of Mn 3ϩ and Mn 4ϩ ions in the superlattice structure promotes the antiferromagnetic long-range order. The absence of a magnetic diffuse peak indicates that a magnetic frustration is removed from LiMn 2 O 4 at low temperatures. The dynamics of the lithium ions are also discussed on the basis of the Debye-Waller factor.

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