Takao Kawai

Hall Effect of Photoelectrons in Cadmium Sulfide

Hall effect of photoelectrons in cadmium sulfide has been studied in the temperature range from room temperature down to 1.8°K using the Redfield method operated by pulse circuits. The low field Hall mobility is found never to decrease at low temperatures in contrast to the previous investigations. The highest observed mobility is 5× 10 4 cm 2 /volt sec at 1.8°K which is the same order of magnitude estimated from the cyclotron resonance measurements. Below 25°K, the mobility increases according to T -1/2 as the temperature is lowered. The general feature of the dependence of low field Hall mobility on temperature is described by the combination of scatterings by optical vibrations of lattice and piezoelectric effects. Anisotropy in mobility is observed only in the temperature region where the piezoelectric scattering dominates. The ratio of µ a to µ c is found to be 1.5±0.1. The results of high magnetic field effect on the Hall effect are analysed by the theory of Burnham, Brown and Knox with the observed...

Study on the Internal Motions of Some Acryl- and Methacryl-group High Polymers by Pulsed NMR Method

The internal motions of some high polymers were investigated by measuring the spin-lattice relaxation time ( T 1 ) together with its minima ( T 1 min ) in proton resonance in the temperature range from liquid air up to about 300°C by pulsed NMR method at 25 Mc/sec. For acryl-group high polymers (PMA, PEA, PEA), two minima of T 1 were observed, one at higher temperature corresponding to the segmental motion and the other at lower temperature to the internal motion of side chain ester alkyl group. For methacryl-group high polymers (PMMA, PEMA, PBMA), three minima of T 1 were observed, of which one at the highest temperature corresponds to the segmental motion, the next at the middle temperature to the internal motion of both main chain methyl group and side chain ester alkyl group and the last at the lowest temperature to the internal motion of the latter group alone. Thus, we could definitely separate the internal motion of amorphous high polymers. The rigorous analysis of the behavior is considered to be ...

Drift Mobilities of Electrons and Holes in Thallous Bromide

Drift mobilities of electrons and holes in TlBr have been measured below and above the Debye temperature of LO-phonons by a transit time technique. They are compared with finite temperature polaron mobility theories. Rather satisfactory agreement between the experiment and the theory is obtained in electron polarons. The temperature dependence of measured hole polaron mobillity is quite different from what is expected from the theory.

Drift Mobility of Electrons in TlCl

The drift mobility of photoelectrons in TlCl has been measured over the temperature range between 90°K and 330°K by a transit time technique in order to study the behavior of finite temperature polarons. The intrinsic mobilities are measured in the whole range of temperature only in zone-refined crystals. They are compared with the theories developed recently for the finite temperature polarons as well as those for the low temperature ones. The agreements are shown to be unsatisfactory. Decrease of the drift mobility at low temperatures as a result of multiple trapping effect due to the presence of shallow traps of 0.05 eV depth is observed in some crystals.

A Study of Sorbed Water on Cellulose by Pulsed NMR Technique

The state of sorbed water on cellulose has been studied by pulsed NMR technique. From the experimental results of spin-lattice relaxation time ( T 1 ) and spin-spin relaxation time ( T 2 ), observed as a spin echo decay time, following conclusions have been derived. (1) Two phases of the sorbed water are classified; the localized and the mobile. (2) The correlation time (τ N ) derived from T 1 using BPP theory, is consistent with that (τ D ) derived from dielectric measurements. (3) T 1 is by one or two order longer than T 2 in contradiction to BPP theory for extremely narrowing case. As an explanation for this fact, we propose that, when we consider about T 2 , the effects of magnetic nuclei contained in the absorbent must be taken into account, though no theory is given. (4) The average life-time of water molecule sorbed on cellulose in the localized state is estimated to be several hundredths of a second and to decrease with temperature.

Two-Carrier Photoconduction in TlCl Crystal

Spectral dependency and electric field dependency of photoconductivity of purified TlCl have been studied at low temperatures, mostly at 17°K and 81°K, by the standard transient method with blocking electrodes and using exciting light of low intensity. When traps in the crystal are empty, higher photoresponses under hole polarity than those under electron polarity have been observed at 17°K and vice versa at 81°K, indicating that the photoconductivity is of two-carrier. The results are analyzed from the standpoint of two-carrier and low field unit ranges of electrons and holes are determined. With these unit ranges, schubwegs of electrons and of holes are estimated as functions of electric field from the field dependence of photoconductivities under both polarities. They obey Ohms law at 81°K but are proportional to E 0.5 above certain critical fields at 17°K. Low field unit range of holes has been found to be larger than that of electrons below 50°K and smaller above this temperature. Effect of filling ...

Effect of Magnetic Soft Mode on 87Rb Nuclear Spin-Lattice Relaxation in Singlet-Ground-State System RbFeCl3

The nuclear spin-lattice relaxation time T 1 of 87 Rb in the singlet-ground-state easy-plane antiferromagnet RbFeCl 3 has been measured at the temperatures above and below T N ≈2.5 K with the external field applied both along and perpendicularly to the hard c -axis. From the analysis based on the dynamical correlated-effective-field approximation, it is found that the trend of the divergence of T 1 -1 in the paramagnetic phase around T N is closely related to the remarkable softening of the magnetic excitation for the K-point mode (\(\bm{q}=\bm{q}_{0}\)) via the in-plane component of the static susceptibility χ (\(\bm{q}_{0}\)).

Study of Nuclear Spin-Lattice Relaxation of 1H and 35Cl in Low-Dimensional Ising-like System; [(CH3)3NH]CoCl3·2H2O

The nuclear srin-lattice relaxation in low-dimensional ferromagnetic Ising-like system has been studied from the temperature and field dependences of T 1 of 1 H and 35 Cl in the ordered state of [(CH 3 ) 3 NH]CoCl 3 ·2H 2 O ( T N =4.135 K). The proton relaxation is analyzed using the theory for the two-magnon process. A reasonable fit between experiment and calculation is obtained at low temperatures by adjusting the magnon gap energy. The 35 Cl relaxation and the deviation of the 1 H data from prediction of the two-magnon process are examined in terms of a new relaxation process which is associated with the scatterins of a two-magnon bound state and a spin-wave. An approximate treatment for this process gives a satisfactory explanation of the experimental results. The effect of transverse exchange anisotropy on the field dependence of T 1 and the importance of the pair-correlation in the 35 Cl relaxation are discussed.

Effect of Domain-Boundary Propagation on 133Cs Nuclear Spin-Lattice Relaxation in One-Dimensional Ising-Like Antiferromagnet CsCoCl3 ·2H2O

The nuclear spin-lattice relaxation time T 1 of 133 Cs in one-dimensional Ising-like antiferromagnet CsCoCl 3 ·2H 2 O was measured in the paramagnetic state where short-range orders are well developed. Most of experimental features were interpreted in terms of the diminution of the longitudinal spin correlation due to the random passings of domain boundaries, which is described by an approximate equation T 1 -1 ∼exp (| J |/ k T ).