M. Koyano

Resonant photoemission studies of 3d transition metal intercalates of TiS2

Abstract Photoemission energy distribution curves, constant initial state (CIS) spectra, and partial yield spectra have been measured on intercalation compounds of Ti1+xS2, Fe 1 3 TiS 2 , and Ni 1 3 TiS 2 over the photon energy range of ℏω = 32−120 eV. In all crystals, a characteristic resonance profile is observed in the CIS spectra at ℏω = 40−55 eV, which is attributed to the transition from Ti 3p to 3d states. The conduction and valence bands of these compounds are influenced by the strong hybridization of Ti 3d, S 3p, and the guest atom 3d orbitals.

High field magnetization of 3d transition metal intercalates MxTiS2 (M = 3d metals)

Abstract High field magnetization has been measured on the single crystals of 3d transition metal intercalates M x TiS 2 (M = Mn, Fe, at 4.2 K in pulsed fields up to 36 T. In particular, Fe x TiS 2 shows a strongly anisotropic hyteresis curve with easy axis parallel to the c -axis, while other intercalates have a paramagnetic behavior. These magnetic properties are understood reasonably in the light of an itinerant electron model or band picture.

Transient thermoelectric effects in intercalation compounds MxTiS2 (M=3d transition metals)

Simultaneous measurements of thermal diffusion processes of electrons and phonons in 1T‐TiS2 and intercalation compounds MxTiS2 (M=Mn, Fe, Co, and Ni; x=0.1–1/3) have been made in the temperature range 78–280 K using a pulsed laser‐induced ‘‘transient thermoelectric (TTE)’’ or photodiffusion effect. The initial stage of the decay curves of TTE voltage observed solely in TiS2 gives the electron‐hole recombination times τr, from which capture cross sections are evaluated. At the second stage, two relaxation times (τf and τs) are observed in all crystals; the fast and slow components are associated with the intra‐ and intervalley scatterings through electron‐phonon interactions, respectively. The evaluation of the final stage yields the thermal diffusion coefficient DT and thermal conductivity κ of these materials. The effect of intercalation of the guest 3d metals on these quantities is qualitatively discussed.

Sliding motion of charge density wave in quasi-two-dimensional η-Mo4O11 crystal

Abstract High electric field measurements of electrical conductivity of the CDW material of quasi-two-dimensional η-Mo4O11 (transition temperatures Tc1 = 105 and Tc2 = 35 K) have been made. Here we show the existence of a sliding motion of depinned CDW condensate above a threshold field Et (= 20−30mV cm−1) in the first CDW state (Tc2

Magnetic scattering of conduction carriers in 3d transition-metal intercalates of M x TiS2 (M=Mn, Fe, Co, and Ni)

Galvanomagnetic measurements on layer-structured 3d transition-metal intercalates of MxTiS2 (M = Mn, Fe, Co, and Ni;x≤0.33) have been made over the temperature range 0.34–20 K. Resistivity minima and negative magneto-resistances are observed for paramagnetic Mn, Fe, and Ni intercalates with low guest concentrations (x≤0.1), as found in well-known dilute alloys. However, in the case of the weak-ferromagnetic phase of CoxTiS2 (0.10≤x≤0.33) with the Curie temperatureTc=120–140 K, such anomalous behaviors are also observed, which is not commonly found in the magnetically ordered phases of various magnetic materials. With these data we have given qualitative discussions on the magnetic scattering process of conduction carriers. Further, some of the experimental results are discussed in connection with the band calculations for M1/3TiS2.

Electron and hole conduction in intercalation compound of NixTiS2

Abstract Electrical resistivity and Hall coefficient of intercalation compound of NixTiS2(0⩽ x ⩽ 0.50) have been measured over the temperature range 1.5–300 K. These transport properties are strongly dependent on the guest Ni concentration x. In particular, with increasing x the Hall coefficient changes its sign from negative to positive at a characteristic concentration of x = 0.33, indicating the appearance of hole pockets in the band structure. A qualitative discussion is given for such a possibility.

High-field galvanomagnetic properties of monoclinic η-Mo4O11 crystal

Transverse magnetoresistance and Hall effect of quasi-two-dimensional crystal of monoclinic η-Mo4O11 have been measured at 4.2 K under pulsed magnetic fields up to 38 T. The Shubnikov-de Haas oscillations were observed in the magnetic field dependent Hall resistivity. In the low field regime H < Hc (= 10T), the conduction is dominated by holes, while in the high field regime above Hc by electrons. From these experimental results we discuss qualitatively on the Fermi surfaces of holes and electrons associated with CDW transitions.

Electrical and thermal properties of intercalation compound FexTiS2

Abstract Intercalation phenomena of guest Fe atoms into van der Waals gaps of the host 1T - TiS 2 layered crystal have been studied by transport measurements. These experimental results, together with other data, are indicative of the presence of spin-up and spin-down bands produced by the host-guest interactions and understood in terms of an itinerant band picture, in agreement with recent band calculations.

Charge-density-wave related quantum transport in monoclinic η-Mo4O11 crystal

Abstract Magnetoresistance and Hall effect of quasi-two-dimensional crystal of monoclinic η-Mo 4 O 11 have been remeasured at 2.2–4.2 K under pulsed magnetic fields up to 40 T. Characteristic hysteresis phenomena are observed in both transverse magnetoresistance and Hall resistivity when a field-sweep range exceeds a threshold value (∼; 10 T), which may possibly be ascribed to a field-induced phase transition from one CDW state to another of the carrier system. The experimental data also show that the carrier system in the CDW state enters further into a quantum-limit regime at higher fields than 25 T.

Spin-glass behavior in itinerant magnetic material of FexTiS2

Hall resistivity ρH and magnetoresistance Δρ/ρ0 in the spin-glass phase of FexTiS2 (x = 0.20) have been measured at 4.2 K under pulsed magnetic fields up to 16 T. The ρH- and Δρ/ρ0- H curves show a hysteresis corresponding to the magnetization curve, and these quantities relax with time t after the field is switched off, obeying the power law of the form, |Δρ/ρ0| =At−m (m = 0.0575) and ρH-Bt−n (n = 0.0258).