Atsushi Teruya

Split Fermi Surface Properties based on the Relativistic Effect in Superconductor PdBiSe with the Cubic Chiral Crystal Structure

We grew single crystals of PdBiSe with the ullmannite-type cubic chiral structure and carried out de Haas–van Alphen (dHvA) experiments to clarify the Fermi surface properties. The Fermi surfaces are found to split into two different Fermi surfaces, reflecting the non-centrosymmetric crystal structure. A splitting energy between two nearly spherical Fermi surfaces named α and α′ is determined as 1050–1260 K. These Fermi surfaces are identified to be due the band-149 and -150 electron Fermi surfaces centered at the Γ point from the results of full-potential linearized augmented plane wave (FLAPW) energy band calculations under consideration of a mass correction in the spin–orbit interaction for Bi-6p electrons based on the relativistic effect. The theoretical splitting energy between these Fermi surfaces is 1080–1150 K, which is in good agreement with the experimental value.

De Haas–van Alphen Effect and Fermi Surface Properties in Nearly Ferromagnet SrCo2P2

We grew high-quality single crystals of SrCo2P2 with the ThCr2Si2-type tetragonal structure, and clarified the Fermi surface properties by carrying out de Haas–van Alphen (dHvA) experiments and energy band calculations. SrCo2P2 is known to be a nearly ferromagnetic compound, where the magnetic susceptibility follows the Curie–Weiss law above 200 K, with the effective magnetic moment μeff = 1.72 μB/Co, but becomes almost constant below about 100 K. The electronic specific heat coefficient γ is thus relatively large, being γ = 40 mJ/(K2·mol). Detected dHvA branches possess the corresponding cyclotron effective masses \(m_{\text{c}}^{*}\), ranging from 0.87 to 7.2 m0 (m0: rest mass of an electron). The angular dependences of the dHvA frequencies are well explained by the results of full-potential linearized augmented plane wave (FLAPW) energy band calculations, revealing a multiply-connected band 25th hole Fermi surface and a compensated nearly cylindrical band 26th electron Fermi surface. It is thus conclud...

Chiral-Structure-Driven Split Fermi Surface Properties in TaSi2, NbSi2, and VSi2

We carried out de Haas–van Alphen (dHvA) experiments for TaSi2, NbSi2, and VSi2 with the hexagonal chiral structure, and compared them with the results of energy band calculations. The Fermi surface is found to be split into two different Fermi surfaces, reflecting the non-centrosymmetric crystal structure. A magnitude of the antisymmetric spin–orbit interaction or a splitting energy between the two Fermi surfaces is determined to be 493 K for dHvA branch α (α′) and 564 K for branch β (β′), where these dHvA branches correspond to main Fermi surfaces. The present splitting values are compared with 209 and 244 K in NbSi2, and 19 and 39 K in VSi2, respectively. The splitting energy is found to be larger in the Ta-5d conduction electrons than those with the Nb-4d and V-3d conduction electrons.

Fermi Surface Properties Based on the Relativistic Effect in SrBi3 with AuCu3-Type Cubic Structure

Bi-6p electrons are well known to possess a strong spin–orbit interaction, but a mass correction based on the relativistic effect is scarcely discussed in the electronic state. To clarify the relativistic properties of Bi-6p electrons, we grew single crystals of SrBi3 with the AuCu3-type cubic structure by the Bi self-flux method and carried out electrical resistivity, specific heat, and de Haas–van Alphen (dHvA) experiments. Several kinds of closed Fermi surfaces are observed from the dHvA effect. Among them, three kinds of main Fermi surfaces are compared with the results of full-potential linearized augmented plane wave (FLAPW) energy band calculations under two considerations. One corresponds to the mass correction in the spin–orbit interaction for Bi-6p electrons. The other is without the mass correction. Detected two kinds of the main Fermi surfaces are well explained with and without the mass correction, but a remaining Fermi surface is explained only with the mass correction. The relativistic effe...

Magnetic and transport properties of EuNi(Si1-xGex)3 compounds

The magnetization M, electrical resistivity ρ, thermopower S and specific heat C of EuNi(Si1-xGex)3 compounds have been measured at temperatures from 2 to 300 K. For the compounds of EuNi(Si1-xGex)3, we obtained an effective magnetic moment of μeff ~ 7.7 μB, which is close to the divalent Eu value of μeff =7.94 μB. All compounds of EuNi(Si1-xGex)3 order antiferromagnetically. The Neel temperature TN decreases monotonously with increasing the Ge concentration x from TN=49 K for EuNiSi3 to TN=14 K for EuNiGe3. In the low temperature region below TN, anomalies corresponding to an additional magnetic phase transition into ferromagnetic state for compounds with x 0.3 were observed. The Curie temperature TC rapidly decreases with increasing x and vanishes at x ≈ 0.3. It is found that the magnetic phase transition temperatures of TN and TC in EuNi(Si1-xGex)3 are strongly connected with the change of volume induced by the atomic substitution of Si by Ge.

Large Cyclotron Mass and Large Ordered Moment in Ferromagnet CoS₂ Compared with Paramagnet CoSe₂

We succeeded in growing high-quality single crystals of the pyrite-type cubic compounds CoSe2 and CoS2 using the transport agent CoBr2 and measured the electrical resistivity, specific heat, magnetic susceptibility, magnetization, and de Haas–van Alphen (dHvA) effect. We confirmed that CoSe2 is an exchange-enhanced paramagnet revealing a broad maximum at around 50 K in the temperature dependence of the magnetic susceptibility. The electronic specific heat coefficient is moderately large, γ = 18 mJ/(K2·mol). On the other hand, CoS2 is a ferromagnet with a Curie temperature TC = 122 K and an ordered moment μs = 0.93 μB/Co. The γ of 21 mJ/(K2·mol) of CoS2 is slightly larger than that of CoSe2. A large ordered moment, together with a large γ, is characteristic of CoS2 because CoS2 is a half-metallic spin state in the ferromagnetic state. Correspondingly, we detected a main dHvA branch with a large cyclotron effective mass of 13m0 in the dHvA experiments. The detected dHvA branches in CoS2 and CoSe2 are discus...

Characteristic Fermi Surface Properties of V2Ga5, CoGa3, TiGa3, ZrGa3, and ZrAl3 with Different Tetragonal Structures

To clarify the Fermi surface properties based on the dimensionality of electronic states, we grew single crystals of V2Ga5, CoGa3, TiGa3, and ZrGa3 (ZrAl3) with different tetragonal structures and carried out de Haas–van Alphen experiments, together with full-potential linearized augmented plane wave band calculations. A nearly one-dimensional plate Fermi surface is obtained in the band calculations for V2Ga5 with a flat tetragonal structure. The corresponding single crystal is of needle shape along the tetragonal [001] direction. The obtained Fermi surfaces of CoGa3 are very similar to those of Ni3Ga with the AuCu3-type cubic structure because the crystal structure of CoGa3 is nearly cubic and the corresponding single crystal is of pyramidal shape with a flat (111) plane. The Fermi surfaces of TiGa3 are also very similar to those of YCu2Si2 with the ThCr2Si2-type tetragonal structure. The cylindrical Fermi surfaces with concave and convex parts are realized in ZrGa3 and ZrAl3 with the flat Brillouin zone...

Pressure and Substitution Effects on Transport and Magnetic Properties of Y1-xRxCo2 Systems with Static Magnetic Disorder

The electrical resistivity and thermopower of light- and heavy-rare-earth-based pseudo-binary Y1-xRxCo2 (R = Nd, Gd, and Tb) alloys are measured at temperatures from 2 to 300 K under pressures up to 3.5 GPa. The resistivity and thermopower of Y1-xRxCo2 show unusual large variations with atomic substitution and pressure in the range of x<xm, where an inhomogeneous magnetization of the Co 3d electron subsystem is observed. These results indicate that the low-temperature transport properties of Y1-xNdxCo2, as well as of Y1-xR\text{HCo2 (R\text{H = heavy rare earth) alloys, are related to conduction electron scattering due to the static magnetic disorder in the itinerant Co 3d electron subsystem. We found that there is a universal relationship between \(\mathrm{d}\ln T_{\text{C}}/\mathrm{d}P\) and \(x/x_{\text{m}}\) in Y1-xRxCo2 alloys, where \(x_{\text{m}}\) is the boundary composition, which separates the alloy phase diagram into regions with uniform and nonuniform magnetizations of the Co-3d electron subsy...

Fermi Surface and Magnetic Properties in Ferromagnet CoS2 and Paramagnet CoSe2 with the Pyrite-type Cubic Structure

We succeeded in growing high-quality single crystals of pyrite-type cubic compounds CoSe2 and CoS2 using a transport agent of CoBr2 and measured the electrical resistivity, specific heat, magnetic susceptibility, magnetization, and the de Haas–van Alphen (dHvA) effect. We confirmed that CoSe2 is an exchange-enhanced paramagnet revealing a broad maximum at around 50 K in the temperature dependence of the magnetic susceptibility. The electronic specific heat coefficient is moderately large, γ = 18 mJ/(K2mol). On the other hand, CoS2 is a ferromagnet with a Curie temperature T C = 122 K and an ordered moment μ s = 0.93 μB/Co. The γ value of 21 mJ/(K2mol) in CoS2 is slightly larger than that of CoSe2. A large ordered moment, together with a large γ value, is a characteristic feature in CoS2 because CoS2 is a half-metallic spin state in the ferromagnetic state. Correspondingly, we detected a main dHvA branch with a large cyclotron effective mass of 13m 0 in the dHvA experiments. The detected dHvA branches in CoS2 and CoSe2 are discussed on the basis of the results of energy band calculations, revealing a broken four-fold-symmetry in the angular dependence of the dHvA frequency.

Superconducting and Fermi Surface Properties of Single Crystal Zr 2 Co

We succeeded in growing single crystals of a superconductor Zr2Co with the tetragonal structure by the Bridgman method and carried out electrical resistivity, magnetic susceptibility, magnetization, specific heat, and de Haas–van Alphen (dHvA) experiments. Superconductivity is a characteristic revealing that the electronic specific heat at 1.45 K in the form of Ce/T in the superconducting state increases not linearly but as a function of \(\sqrt{H} \) up to a magnetic field close to the upper critical field Hc2 = 11 kOe. The superconducting transition temperature Tsc is found to increase markedly with increasing pressure from Tsc = 5.2 K at ambient pressure to 9.5 K at 8 GPa. From the dHvA experiment, several kinds of dHvA branches are detected, which are well explained by the results of the energy band calculation. The main conduction electrons are Zr-4d and Co-3d electrons.