Takehito Suzuki

Extremely high electron mobility in a phonon-glass semimetal

The electron mobility is one of the key parameters that characterize the charge-carrier transport properties of materials, as exemplified by the quantum Hall effect as well as high-efficiency thermoelectric and solar energy conversions. For thermoelectric applications, introduction of chemical disorder is an important strategy for reducing the phonon-mediated thermal conduction, but is usually accompanied by mobility degradation. Here, we show a multilayered semimetal β-CuAgSe overcoming such a trade-off between disorder and mobility. The polycrystalline ingot shows a giant positive magnetoresistance and Shubnikov de Haas oscillations, indicative of a high-mobility small electron pocket derived from the Ag s-electron band. Ni doping, which introduces chemical and lattice disorder, further enhances the electron mobility up to 90,000 cm(2) V(-1) s(-1) at 10 K, leading not only to a larger magnetoresistance but also a better thermoelectric figure of merit. This Ag-based layered semimetal with a glassy lattice is a new type of promising thermoelectric material suitable for chemical engineering.

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 .

Nonvolatile memory effect of capacitance in polycrystalline spinel vanadate

The authors found that capacitance of polycrystalline spinel FeV2O4 exhibits a magnetic-field dependence with hysteresis and takes two values at zero field depending on the direction of a small magnetic field (∼1000G) applied prior to measurement. This behavior can be potentially used as a nonvolatile memory device in which the data are stored as a difference of capacitance through the change of magnetic-field directions.

Modification of electronic structure and thermoelectric properties of hole-doped tungsten dichalcogenides

We present a study on the modification of the electronic structure and hole-doping effect for the layered dichalcogenide WSe_2 with a multi-valley band structure, where Ta is doped on the W site along with a partial substitution of Te for its lighter counterpart Se. By means of band-structure calculations and specific-heat measurements, the introduction of Te is theoretically and experimentally found to change the electronic states in WSe_2. While in WSe_2 the valence-band maximum is located at the Gamma point, the introduction of Te raises the bands at the K point with respect to the Gamma point. In addition, thermal-transport measurements reveal a smaller thermal conductivity at room temperature of W_1-xTa_xSe_1.6Te_0.4 than reported for W_1-xTa_xSe_2. However, when approaching 900 K, the thermal conductivities of both systems converge while the resistivity in W_1-xTa_xSe_1.6Te_0.4 is larger than in W_1-xTa_xSe_2, leading to comparable but slightly smaller values of the figure of merit in W_1-xTa_xSe_1.6Te_0.4.

Coupling between magnetic, dielectric properties and crystal structure in MnT2O4 (T = V, Cr, Mn)

We measured the temperature dependence of dielectric constant and striction for spinel MnT2O4 (T = V, Cr, Mn) under magnetic field. We found critical changes of the dielectric constant and striction with ferrimagnetic ordering as well as applied magnetic field in MnV2O4 and Mn3O4, which have orbital degree of freedom in the T3+ ion. This result indicates the importance of the orbital degree of freedom for the coupling between dielectric, magnetic properties and crystal structure in these spinel compounds.

Low temperature structural instability of tetragonal spinel Mn 3O4

Tetragonal ferrimagnetic spinel Mn3O4 shows complex magnetic phase transitions due to competing anti ferromagnetic interactions involving Mn2+/3+ ions with difference valences. Using magnetization and neutron diffraction measurements, we propose that its tetragonal lattice possesses an instability towards orthorhombic distortion in zero field well below \(T_{\text{N}}\). The direction of the observed instability suggests that the anomaly is related to lifting of the persistent geometrical frustration via spin–lattice coupling.

Extreme magnetoresistance in magnetic rare-earth monopnictides

The acute sensitivity of the electrical resistance of certain systems to magnetic fields known as extreme magnetoresistance (XMR) has recently been explored in a new materials context with topological semimetals. Exemplified by WTe

Second Harmonic Generation from Multiferroic MnWO4

_{2}

Magnetocapacitance in Geometrically Frustrated Magnet ZnFe2O4

and rare earth monopnictide La(Sb,Bi), these systems tend to be non-magnetic, nearly compensated semimetals and represent a platform for large magnetoresistance driven by intrinsic electronic structure. Here we explore electronic transport in magnetic members of the latter family of semimetals and find that XMR is strongly modulated by magnetic order. In particular, CeSb exhibits XMR in excess of

Electronic transport on the Shastry-Sutherland lattice in Ising-type rare-earth tetraborides

1.6 \times 10^{6}