H. Negishi

Pulsed laser‐induced transient thermoelectric effects in silicon crystals

A new technique is described in which a transient thermoelectric (TTE) voltage of a semiconductor is measured after a pulsed laser irradiation—a modification of photodiffusion or Dember effect. This technique has been successfully applied to test samples of n‐ and p‐Si over the wide time range from 20 ns to 2 s and the temperature 120–284 K. The decay curves of the TTE voltage consist of three stages with the characteristic relaxation or decay times. Stage 1 with the relaxation time τ1, is associated with the carrier generation and recombination and explained by the Dember effect. Stage 2 characterized by the relaxation time τ2, is due to the diffusion of majority carriers from a higher to a lower temperature region; for p‐Si, a double‐relaxation process is observed arising from the difference in the drift mobilities of light and heavy holes. At stage 3, the TTE voltage vanishes completely, which can be reasonably interpreted by the diffusion of thermal flux or phonons along a temperature gradient produce...

Magnetic properties of intercalation compounds MxTiS2 (M = 3d transition metal)

Abstract Magnetization measurements have been made on 3d transition-metal intercalation compounds of M x TiS 2 (M = V, Cr, Mn, Fe, Co and Ni; 0 ⩽ x ⩽ 1) at 4.2, 77 and 300 K in static fields up to 20 kOe and in pulsed fields up to 160 kOe. The ac magnetic susceptibility measurements in dc fields have also been made for Fe x TiS 2 . We have identified various types of magnetic phases in M x TiS 2 , such as paramagnetic, spin-glass, cluster-glass or mictomagnetic, and ferromagnetic ones, depending on the kind of guest 3d metals and their concentrations. Magnetic properties of these materials can be understood in terms of an itinerant or band picture rather than a localized or rigid band model.

Specific heat measurements of intercalation compounds M x TiS2 (M=3d transition metals) using ac calorimetry technique

Specific heats of 3d transition metal intercalates of 1T-CdI2-type TiS2, MxTiS2 (M=V, Cr, Mn, Fe, Co, and Ni; 0≤x≤1), have been measured in the temperature range 1.6–300 K using an ac calorimetry technique. The electronic specific heat coefficient γ (2–100 mJ/mole K2) and the Debye temperature ϑD (240–430 K) are found to depend on the guest 3d metals and their concentrations. All the intercalates show anomalous specific heat at low temperatures following an α–δ lnT dependence (α and δ are constants), as found in dilute alloys.

Linear and nonlinear AC magnetic susceptibilities in intercalation compound FexTiS2

Abstract The harmonic, second and third higher harmonic components of the induced voltage of a sample coil under application of a low-field ac magnetic field, with and without static field, have been measured in the spin-glass, cluster-glass, and ferromagnetic phases of the intercalation compound Fe x TiS 2 over the temperature range 1.5-300 K. Using a phenomenological expression for the magnetization, we have obtained independently the relative magnitudes of the linear and nonlinear ac magnetic susceptibilities χ 0 , χ 1 and χ 2 for each magnetic phase.

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.

Thermoelectric Power and Scattering of Carriers in Bi2—xSnxTe3 with Layered Structure

Thermoelectric power, electrical resistivity, and Hall effect of p-type Bi2—xSnxTe3 (0 ≤ x ≤ 0.030) single crystals have been measured in the temperature range 4.2 to 300 K. By doping Sn atoms into the host Bi2Te3 lattice, enhancements in the thermopower and resistivity are observed in the intermediate temperature range 30 to 150 K, and activation type behaviors are found in the resistivity versus temperature curves with an activation energy of the order of 10 meV which corresponds to the Sn-induced impurity band located above the second lower valence band. For our experimental results, we have also given a qualitative discussion about the scattering mechanism. Thermospannung, elektrischer Widerstand und Halleffekt von p-Bi2—xSnxTe3 (0 ≤ x ≤ 0,030) Kristallen werden bei Temperaturen von 4,2 bis 300 K gemessen. Die Dotierung mit Sn-Atomen in den Bi-Schichten von Bi2Te3 erhoht die Thermospannung und den Widerstand in einem mittleren Temperaturgebiet von 30 bis 150 K, und die Temperaturabhangigkeit des Hallkoeffizienten oder des Widerstands ergibt eine Aktivierungsenergie in der Grose von 10 meV, die dem Sn-induzierten Fremdband, das oberhalb des zweitniedrigsten Valenzbands liegt, entspricht. Fur diese experimentellen Ergebnisse geben wir eine qualitative Diskussion uber das Bandmodel und den Einflus der Sn-Dotierung auf die elektronischen Eigenschaften.

ESR Studies on 3d Transition Metal Intercalation into Layered TiS2 Crystals

Extensive X-band ESR measurements have been made on the 3d transition metal intercalation compound M x TiS 2 (M=V, Cr, Mn, Fe, Co, Ni; 0≤ x ≤1) over the temperature range 300–77 K. The variations of the intra- and interlayer spacings with intercalation of guest atoms are presented. Fe and Ni intercalates do not show any ESR signals. Magnetic interactions are ineffective in V x TiS 2 , while in Cr x TiS 2 and Mn x TiS 2 dipolar interactions are dominant and these paramagnetic atoms undergo a thermally activated motion in the interlayers. Co x TiS 2 becomes ferromagnetic below T c (<140 K) and their temperature dependence of linewidth is very similar to those in itinerant ferromagnets like CoS 2 , suggesting the formation of a low spin state near the host Ti d-band. The anisotropies in the g -value and linewidth are notable in these layered intercalates.

Photoemission Studies on Intercalation Compounds of MxTiS2 (M=3d Transition Metals)

Effect of 3d transition metal intercalation into 1T-CdI 2 type TiS 2 layered crystals, expressed as M x TiS 2 (M=Mn, Fe, Co and Ni), has been studied by synchrotron radiation photoemission over the photon energy range of \(\hbar\omega=32\text{--}120\) eV. The spectra are found to depend strongly on the guest 3d metals and their conacentration. The valence bands are modified by the strong hybridization of Ti 3d, S 3p states and the guest atom 3d states, in good agreement with a theoretical prediction.

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.

Chemical Vapor Growth and Manganese Metal Intercalation of TiS2

TiS 2 crystals with a 1T-CdI 2 type layered structure have been grown by a chemical vapor reaction under different conditions of transport gas, size of ampoule, and temperature. Various attempts to intercalate Mn metals into the TiS 2 layers were made using electrochemical, dipping in pyridine solution, thermal diffusion, and direct reaction methods. The EPR signals of the Mn-intercalated TiS 2 show a Mn 2+ state with the g -value≈2 and the hyperfine structure constant. A =80 ×10 -4 cm -1 , indicating a strong ionic nature of the crystalline environment. A lattice expansion along the c -axis upon intercalation is discussed.