Hajime Sagayama

Structural and Magnetic Properties of Spinel FeV2O4 with Two Ions Having Orbital Degrees of Freedom

Spinel FeV 2 O 4 with orbital degrees of freedom both at the Fe 2+ and V 3+ ions exhibits successive structural phase transitions. We studied this structural and magnetic properties as well as the correlation between the two. We found that the crystalline domains in the tetragonal or orthorhombic phases can be aligned by the applied magnetic field, inducing a large magnetostriction (∼1%). The competition and cooperation of Fe 2+ and V 3+ orbitals is the possible origin of these intriguing properties in FeV 2 O 4 .

Orbital dilution effect in ferrimagnetic Fe1 ? xMnxCr2O4: competition between anharmonic lattice potential and spin?orbit coupling

Magnetic and structural phase diagram in a spinel-type solid solution system Fe(1-x)Mn(x)Cr(2)O(4) has been investigated. The cubic-to-tetragonal transition temperature T(s 1) is gradually reduced by the substitution of Mn(2+) (3d(5)) for Jahn-Teller-active Fe(2+) (3d(6)) ions, implying the long-range nature of the ferroic interaction between orbitals. In the paramagnetic tetragonal phase for x < 0.5, the c parameter is shorter than a because of the anharmonicity of the elastic energy. The crystal structure further changes to orthorhombic at around the ferrimagnetic transition temperature T(N 1). T(s 1) and T(N 1) meet at x = 0.5, and Mn substitution of more than 0.5 gives rise to another tetragonal phase with a < c. The systematic change in crystal structure is discussed in terms of competition between the anharmonic lattice potential and the intra-atomic spin-orbit interaction at Fe(2+).

Two Types of Multistack Structures in MgB2-Type Superconductor CaAlSi

Crystal structure analysis of an AlB 2 -type superconductor, CaAlSi, has been carried out using synchrotron X-rays and neutron diffraction measurements. Two different stackings along the c -axis–5-...

Structural Transformation on the Pressure-Induced Metal–Insulator Transition in PrFe4P12

We report the first X-ray diffraction experiments of PrFe 4 P 12 under high pressure. We discovered a symmetry lowering from cubic to orthorhombic or lower at the metal–insulator transition temperature, accompanied by a jump in the lattice constant, which indicates a first-order phase transition. The superlattice reflections at q =(1,0,0) observed in the low-pressure nonmagnetic ordered phase are found to disappear in the insulating phase. The temperature dependence of the lattice constant and the absence of the superlattice reflections are well explained by taking into account an antiferromagnetic ordering.

Magnetic-field effects on Jahn-Teller distortion in ferroelastic magnetic insulator Fe1−xMnxCr2O4

The magnetic field response of Jahn-Teller distortion associated with the e orbital was investigated by x-ray diffraction in Fe1−xMnxCr2O4 for x = 0 and 0.7. Successive structural domain rearrangements occurred when a magnetic field was applied along the [001]c axis in the orthorhombic phase of FeCr2O4. The domain rearrangements caused significant magnetostriction, which was observed by using a strain gauge. Reversible magnetostriction also appeared just above the structural transition temperature TS1 in Fe0.3Mn0.7Cr2O4, in which TS1 meets the ferrimagnetic transition temperature TN1 by Fe substitution.

Solvent-induced on/off switching of intramolecular electron transfer in a cyanide-bridged trigonal bipyramidal complex.

A cyanide-bridged [Co3Fe2] cluster with trigonal bipyramidal geometry shows solvent-driven reversible on/off switching of its thermally induced electron-transfer-coupled spin transition (ETCST) behaviour.

Observation of Spin Helicity Using Nonresonant Circularly Polarized X-ray Diffraction Analysis

We have successfully detected spin chirality in prototypical multiferroic MnWO 4 wherein the helical magnetic order induces ferroelectricity using a nonresonant circularly polarized X-ray diffraction technique. The intensity of the magnetic reflection from MnWO 4 shows a clear difference between the right- and left-handed circular polarizations of the incident X-ray beam. The ratio of these intensities is in good agreement with theoretical predictions. The results clearly show that this technique is suitable for the investigation of spin chirality. Finally, we studied the spin chirality of another multiferroic material, DyMnO 3 . Possible applications of this technique are also discussed.

Magnetic and transport properties of Gd3Ir4Sn13 with unique crystal structure

We have performed an epithermal neutron scattering experiment along with magnetic susceptibility, resistivity, Hall effect, X-ray diffraction measurements on single crystals grown for the first time. The primary crystal structure was classified into the same structure as that of Yb 3 Rh 4 Sn 13 with the space group P m \bar3 n . However the crystal distortion characterized by (1/2, 1/2, 0) was observed at room temperature by X-ray diffraction. The magnetic susceptibility and resistivity showed an anomaly at 10 K indicating a magnetic phase transition. The epithermal neutron diffraction clarified that an antiferromagnetic order with the propagation vector (100) exist below 10 K. Overall features of transport properties in Gd 3 Ir 4 Sn 13 are similar to those in La 3 Ir 4 Sn 13 .

Three superconducting phases with different categories of pairing in hole- and electron-doped LaFeAs1−xPxO

The phase diagram of the

High-pressure synthesis of an unusual antiferromagnetic metal CaCoO3 with GdFeO3 -type perovskite structure

{\mathrm{LaFeAs}}_{1\ensuremath{-}x}{\mathrm{P}}_{x}\mathrm{O}