Riki Kobayashi

Novel Phase Transition and the Pressure Effect in YbFe2Al10-type CeT2Al10 (T = Fe, Ru, Os)

We have succeeded in growing single crystals of orthorhombic Ce T 2 Al 10 ( T =Fe, Ru, and Os) by the Al self-flux method for the first time, and measured their electrical resistivity ρ at pressures of up to 8 GPa, magnetic susceptibility χ, and specific heat C at ambient pressure. The results indicate that Ce T 2 Al 10 belongs to the heavy fermion compounds. CeRu 2 Al 10 and CeOs 2 Al 10 show similar phase transitions at T 0 =27.3 and 28.7 K, respectively. The temperature dependences of ρ, χ, and C in the ordered phases are well described by the thermally activated form, suggesting that a partial gap opens over the Fermi surfaces below T 0 . When pressure is applied to CeRu 2 Al 10 , T 0 disappears suddenly between 3 and 4 GPa, and CeRu 2 Al 10 turns into a Kondo semiconductor, and then into a metal. The similarity of Ce T 2 Al 10 compounds under respective pressures suggests a scaling relation by some parameter controlling the unusual physics of these compounds.

Long-range order and low-energy magnetic excitations in CeRu2Al10 studied via neutron scattering

= 27 K wasinvestigated by neutron scattering. Powder diffraction patterns show clear superstructure peakscorresponding to forbidden (h+ k)-odd reflections of the Cmcm space group. Inelastic neutronscattering experiments further reveal a pronounced magnetic excitation developing in the orderedphase at an energy of 8 meV.

Magnetic Structure Determination of CeT2Al10 (T = Ru and Os): Single Crystal Neutron Diffraction Studies

Neutron diffraction studies of Ce T 2 Al 10 ( T = Ru and Os), which shows an anomalous transition at T 0 = 27 K for CeRu 2 Al 10 and at 29 K for CeOs 2 Al 10 , have been carried out using single crystal samples of the compounds. In the ordered state below T 0 , obvious superlattice reflections have been found, indicating the appearance of ordered magnetic moments. The magnetic structures of both compounds could be commonly explained with a propagation vector q = (0, 1, 0), where collinear antiferromagnetic moments with magnitudes of 0.42(1) µ B for CeRu 2 Al 10 and of 0.29(1) µ B for CeOs 2 Al 10 are aligned along the c -axis.

Anisotropic Spin Dynamics in the Kondo Semiconductor CeRu 2 Al 10

Spin dynamics in the new Kondo insulator compound CeRu2Al10 has been studied using unpolarized and polarized neutron scattering on single crystals. In the unconventional ordered phase forming below T0=27.3  K, two excitation branches are observed with significant intensities, the lower one of which has a gap of 4.8±0.3  meV and a pronounced dispersion up to ≈8.5  meV. Comparison with random-phase approximation magnon calculations assuming crystal-field and anisotropic exchange couplings captures major aspects of the data, but leaves unexplained discrepancies, pointing to a key role of direction-specific hybridization between 4f and conduction band states in this compound.

Marked Change in the Ground State of CeRu2Al10 Induced by Small Amount of Rh Substitution

We have investigated the marked change in the magnetic properties of CeRu2Al10 induced by a small amount of Rh substitution [Ce(Ru0.95Rh0.05)2Al10]. The magnetic susceptibility along the \(a\)-axis (χa) shows a large decrease with decreasing temperature after showing a sharp peak at \(T_{0}=24\) K and the high field magnetization for the magnetic field along the \(a\)-axis exhibits a spin-flop transition at \({\sim}13\) T. These indicate that the antiferromagnetic (AFM) order where the AFM moment is parallel to the \(a\)-axis takes place, which is consistent with the anisotropy of χa>χc>χb in the paramagnetic region, being different from the AFM order in CeRu2Al10. These results were analyzed by mean field calculation for the two-sublattice model using the crystalline electric field level scheme by Strigari et al. [Phys. Rev. B 86 (2012) 081105]. On the basis of both experimental and calculated results, we conclude that, by a small amount of Rh substitution with one extra \(4d\) electron, the large \(c\)–...

Semiconducting behavior in CeFe2Al10 and CeRu2Al10 single crystals

We have firstly succeeded in growing orthorhombic YbFe2Al10-type CeFe2Al10 and CeRu2Al10 single crystals by Al self-flux method, and measured the electrical resistivity ρ and magnetic susceptibility χ. Both compounds show negative temperature coefficient in ρ above ~100 K. The ρ(T) of CeFe2Al10 shows a broad peak at around 100 K and increases again at low temperatures, suggesting semiconducting ground state. The ρ(T) of CeRu2Al10 shows an abrupt increase below T0=27.3 K and and metallic behavior at low temperatures. The χ(T) exhibits uniaxial magnetic anisotropy along the b-axis for CeFe2Alio and c-axis for CeRu2Al10. CeRu2Al10 shows a sudden drop at T0 in χ(T), indicating some kind of phase transition at T0- Since both compounds have smaller cell volumes than those expected from lanthanoid contraction, these anomalous behaviors should be related to the strong 4f- and conduction-electron hybridization.

Magnetic instability induced by Rh doping in the Kondo semiconductor CeRu2Al10

Magnetic ground state of Rh-doped Kondo semiconductor CeRu

Relation betweenc−fhybridization and magnetic ordering inCeRu2Al10: An optical conductivity study ofCe(Ru1−xRhx)2Al10 (x≤0.05)

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Influence of Electron Doping on Magnetic Order in CeRu2Al10

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Muon sites in Ce(Ru,Rh)2Al10 investigated by using Density Functional Theory from the view point of electronic potential

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