Nakao Hironori

Simultaneous Occurrence of an Antiferroquadrupolar and a Ferromagnetic Transitions in Rare-Earth Palladium Bronze CePd3S4

Neutron powder diffraction experiments have been performed on CePd 3 S 4 as well as measurements of magnetic and transport properties on a single-crystalline sample. Magnetic susceptibility increases markedly below T C = 6.3 K and a spontaneous magnetization appears below T C . The logarithmic temperature dependence of electrical resistivity implies that CePd 3 S 4 is classified into a Kondo-lattice compound whose Kondo temperature is comparable to T C . Magnetic susceptibility is analyzed satisfactorily with a crystalline electric field model that the 4 f ground state of Ce 3+ is the Γ 8 quartet with the excited Γ 7 doublet located at 630 K. The magnetic structure of CePd 3 S 4 was determined to be a canted structure with a canting angle of 51°. Such a canted structure is a result of the ferromagnetic (FM) ordering and simultaneous [100]-type antiferroquadrupolar (AFQ) ordering at T C . The smaller magnetization values and an unexpectedly high T C can be explained by the simultaneous occurrence of AFQ an...

Resonant X-ray Studies of the Quadrupolar Orderings in RB2C2 (R = Dy, Ho)

We have performed the resonant x-ray scattering experiment on DyB 2 C 2 and HoB 2 C 2 , where the antiferroquadrupolar orders play important roles. The superlattice reflections that appear below the transition temperatures have been investigated by measuring the incident energy, polarization, scattering vector, azimuthal angle and temperature dependences at the L 3 absorption edge. The results are theoretically analyzed with a model of the antiferroquadrupolar order: the azimuthal angle dependences are well explained. The quadrupolar and magnetic contributions to the scattering intensities are also separated: it is deduced that the magnitude of the ordered quadrupolar moments of HoB 2 C 2 is much smaller than that of DyB 2 C 2 .

Resonant X-ray Scattering Experiments on the Ordering of Electronic Degrees of Freedom

Resonant X-ray scattering (RXS) has been developed as a powerful technique for observing orderings of electronic degrees of freedom: charge, spin, orbital, and multipoles. After a brief introduction of the RXS technique, we review some RXS experiments on the orderings in \(d\) and \(f\) electron systems with a strong correlation between electrons. The basic concept of RXS and the recent developments of the technique are described in this review paper. We also present future prospects of the studies using RXS for users.

Correlation between Tc and Transport Properties in PrFeP1-xAsxO0.9F0.1

We investigated the isovalent P/As substitution effect in iron pnictide superconductor, PrFeP 1- x As x O 0.9 F 0.1 to find the relationship among superconducting transition temperature T c , crystal structure and electronic properties. The lattice constants and the pnictogen height from iron layer show linear x dependence, indicating the continuous change of chemical pressure without the variation of band filling. In contrast to the monotonic change of crystal structure, T c , the temperature dependence of resistivity and Hall coefficient R H show anomalous x dependence. In the region of the As concentration of 0≤ x ≤0.6, the T c continuously increases, and the power of temperature of resistivity ( n ) is gradually changed from 2 to 1 with increasing x . The T c and the power n show distinct correlation, indicating that the antiferromagnetic fluctuation enhances T c . On the other hand, T c and the power n have no correlation in the region of 0.6 < x ≤1.0. These different behaviors in the regions of x < ...

Pressure Effects on an S = 1 Haldane Compound Ni(C5H14N2)2N3(PF6)

The pressure effects on an S = 1 Haldane compound Ni(C 5 H 14 N 2 ) 2 N 3 (PF 6 ) (NDMAP) have been investigated through the magnetic susceptibility (χ) measurements using single crystalline sample...

Structural Aspects of NaV 2O 5 under High Pressure

Anomalous lattice properties and structural phase transition of NaV 2 O 5 have been studied under hydrostatic high pressure at room temperature by using powder X-ray diffraction techniques. Upon compression the c -axis along the stacking direction of V 2 O 5 -layers contracts rapidly and the b -axis along the one-dimensional magnetic ladder direction expands, while the a -axis contracts up to about 4 GPa and then begins to expand. Structural analysis of NaV 2 O 5 and the previous data of V 2 O 5 indicate that Na atoms between the V 2 O 5 -layers govern these lattice properties. A structural phase transition is found to take place around 13 GPa. A detailed structure analyzed by the Rietveld method reveals that the approach of an apical oxygen of the VO 5 -pyramid to the V atom in the upper VO 5 -pyramid plays an important role in the phase transition. The present crystal field calculation shows the stability of the d x y -like orbital under the high pressure.

Absence of Magnetic Long Range Order in Ba3ZnRu2O9: A Spin-Liquid Candidate in the S = 3/2 Dimer Lattice

We have discovered a novel candidate for a spin liquid state in a ruthenium oxide composed of dimers of S = 3/2 spins of Ru5+, Ba3ZnRu2O9. This compound lacks a long range order down to 37 mK, which is a temperature 5000-times lower than the magnetic interaction scale of around 200 K. Partial substitution for Zn can continuously vary the magnetic ground state from an antiferromagnetic order to a spin-gapped state through the liquid state. This indicates that the spin-liquid state emerges from a delicate balance of inter- and intra-dimer interactions, and the spin state of the dimer plays a vital role. This unique feature should realize a new type of quantum magnetism.We have discovered a novel candidate for a spin liquid state i n a ruthenium oxide composed of dimers of S = 3/2 spins of Ru, Ba3ZnRu2O9. This compound lacks a long range order down to 37 mK, which is a temperature 5000times lower than the magnetic interaction scale of around 20 0 K. Partial substitution for Zn can continuously vary the magnetic ground state from an antiferromagnetic order to a s pin-gapped state through the liquid state. This indicates that the spin-liquid state emerges from a delicate balance o f interand intra-dimer interactions, and the spin state of the dimer plays a vital role. This unique feature should realize a new type of quantum magnetism.

Quadrupolar Order and Structural Phase Transition in DyB4 with Geometrical Frustration

Structural phase transition accompanying with quadrupolar ordering in DyB 4 with Shastry–Sutherland type geometrical frustration has been studied by X-ray diffraction. Previous study [D. Okuyama et al. : J. Phys. Soc. Jpn. 74 (2005) 2434.] using resonant X-ray scattering revealed short-range ordering of the O z x -type quadrupolar moments and the c -plane component of the magnetic moments in addition to long-range ordering of the c -axis component of the magnetic moments. The present report focuses on the lattice distortion below the quadrupolar ordering temperature at T N2 =12.7 K. The (0 0 l =integer) fundamental lattice reflection splits into four peaks along the h and k directions and the ( h =even 0 0) reflection becomes broad along the l direction. This indicates that a structural transition from tetragonal to monoclinic takes place below T N2 together with the ordering of the quadrupolar moments.

Pressure-Induced Phase Transition in NaV 2O 5 at Low Temperature

Pressure effect on phase transition in NaV 2 O 5 has been studied at low temperature by x-ray scattering. In addition to two well-known phases at ambient pressure such as P-phase ( a × b × c orthorhombic unit cell at T > T c 0 = 35 K) and C\(_{\frac{1}{4}}\)-phase (2 a ×2 b ×4 c supercell at T < T c 0 ), we discovered a new high-pressure phase C 0 -phase, which has a 2 a ×2 b ×1 c supercell and is considered to be a new ground state above 0.92 GPa at T <20 K. By measuring temperature dependence of superlattice intensity from the single crystal up to 1.24 GPa for the C\(_{\frac{1}{4}}\)- and C 0 -phases, we obtain the temperature-pressure phase diagram. The P-to-C\(_{\frac{1}{4}}\) phase transition is significantly suppressed as ( d T c 0 / d P )∼-11(1) (K/GPa) at 0.1 MPa (1 atm.) while the C\(_{\frac{1}{4}}\)-to-C 0 phase transition takes place at P c = 0.92 GPa nearly independent of temperature below 20 K.

Magnetic Phase Diagrams of YVO3 and TbVO3 under High Pressure

Magnetic states in R VO 3 ( R = Y, Tb) were investigated using low-temperature and high-pressure neutron-diffraction techniques, and the pressure–temperature magnetic phase diagrams were clarified up to 6.2 GPa. We elucidated that, on application of pressure, the magnetic ground state changes from C -type spin ordering ( C -SO) to G -type spin ordering ( G -SO); this corresponds to the orbital ground-state switching from G -type orbital ordering ( G -OO) to C -type orbital ordering ( C -OO). It is also interesting that the G -SO transition occurs simultaneously with the C -OO transition, but not with the G -OO one. When the transition temperature of C -OO exceeds that of G -OO under high pressure, the G -OO phase vanishes completely, and a simultaneous spin and orbital order–disorder phase transition occurs. Such a transition is the first case in perovskite-type transition-metal oxides.