Katsutoshi Iwahashi

Experimental Studies of Rhombohedral Cr2S3 Single Crystal. I. Magnetic Properties

The magnetic properties of rhombohedral Cr 2 S 3 single crystals were investigated. The remarkable temperature dependences of the small spontaneous magnetization, the magnetic susceptibilities and ...

Spin Wave in Solid 3He

Using the spin wave theory a few thermodynamic quantities of solid 3 He in the “uudd” phase are calculated. In the first approximation, in which higher terms than the fourth power of Holstein-Primakoff operators are neglected, the contraction of the spin is not small and the gain of the energy at 0 K due to the zero point motion of spins is comparable to the energy associated with the molecular field approximation. If only j t and K P are not zero, this approximation does not explain the experimental results. In the second approximation, in which the contribution due to the fourth power terms is taken into account, the “uudd” phase becomes stable or metastable because of large zero point motion of spins even when J 2 - K F <0, and the exchanges that only j t and K P are not zero, can explain the experimental results, where j t , K P and K F are the triple, planar and folded type cyclic four spin exchanges.

Four Spin Exchange Model and Nuclear Antiferromagnetic Resonance in Solid 3He

Using the spin Hamiltonian, in which interactions up to third neighbors and two kinds of large planar and folded cyclic four spin exchange terms were taken into account, we calculated the resonance frequencies of the nuclear antiferromagnetic resonance in solid 3 He observed recently by Osheroff, Cross and Fisher. The typical examples of exchange integrals with which previous experiments can be explained and the corresponding physical quantities are shown.

Experimental Studies of Rhombohedral Cr2S3 Single Crystal. II. Hopping Conductivity Dependent on Magnetic Order

The electrical conductivity and magneto-resistance of CrS x ( x =1.50, 1.47 and 1.42) single crystals were measured as functions of temperatures. These results were compared with the calculations of the conductivity based on the hopping conduction model in which the effects of the magnetic ordering are taken into account. The conductivity of CrS x was well described by the hopping mechanism which an electron hopping occurs within one magnetic sublattice. The temperature dependence of the susceptibility of the sublattice magnetization of b -site were evaluated from the measured negative magneto-resistance of CrS 1.50 .

Magnetic Phase Transitions in Body-Centered Cubic Solid ^3He

Using the Green-function method with Tyablikov decoupling, we have considered theoretically the magnetic properties of the high-field magnetically ordered phase of bcc solid 3 He at low temperatures. Taking into account all exchange processes up to 6 spins, the detailed behaviors of the upper critical field, sublattice magnetization and magnetization were calculated.

ESR and Nonresonant Microwave Absorption in a High-Tc Superconductor of the Tl-Ba-Ca-Cu-O System

Electron spin resonance (ESR) in a high-Tc superconductor of the Tl-Ba-Ca-Cu-O system is observed. Two components of ESR exist. Above 140 K, the intensity of the ESR signal increases as the temperature decreases. Below 140 K, the signal intensity decreases as the temperature decreases and disappears at Tc (124 K), clearly indicating the relation to the superconductivity. Nonresonant absorption is greatly enhanced at Tc. Below Tc, an abrupt change in the derivative curve of the nonresonant microwave absorption occurs at the magnetic field corresponding to the lower critical field.

On the exchange parameters of bcc solid 3He

Using the spin Hamiltonian, in which two‐spin interactions up to third neighbors and two kinds of large folded and planar cyclic four‐spin exchange terms are included, spin wave spectrum of ‘‘uudd’’ and ‘‘pseudoferromagnetic (PF)’’ phase of bcc solid 3He in finite magnetic field has been calculated. The necessary conditions for the exchange parameters to explain the first order phase transiiton from ‘‘uudd’’ to ‘‘PF’’ at magnetic field of about 0.4T and high temperature experimental results have been obtained within a framework of a three‐parameter model. By a calculation using a mean field approximation, the new phase, double spiral spin configuration has been found, and the possibility of the appearance of this phase near TN are discussed.

Scaling behavior in the irreversibility of Tl2Ba2Ba2Ca2Cu3O10 superconductors investigated through microwave absorption

Abstract Irreversibility behavior of Tl2Ba2Ca2Cu3O10 superconducting powders has been studied by observing the temperature-dependent microwave absorption under various magnetic history and field values. The irreversibility temperature scaled with the applied field as H 1 3 , in accordance with the previous results for the Bi-based high-Tc superconductor. The H 1 3 behavior has been interpreted by a thermal activation of vortices from the intrinsic pinning site (TlO or BiO layers) in quasi-two-dimensional systems. We propose a heuristic formulation for the pinning potential U 0 ∝ H −1 2 which semi-quantitatively explains the experimental results.

Electrical resistivity of nonsuperconducting La4BaCu5O13 and La5SrCu6O15-based compounds down to the mK temperature range

Abstract We have measured the electrical resistivity of La 4 BaCu 5 O 13 and La 5 SrCu 6 O 15 -based compounds down to 39mK and 16mK, respectively, without observing superconductivity. When the resistivity ϱ − ϱ 0 was proportional to T γ , the exponent γ ranged from 1.18 to 1.83 for these compounds, where ϱ 0 is residual resistivity and T is temperature. It was ascertained from our measurements down to the mK range that these compounds were not superconducting because of a three-dimensional network of CuO 5 units.

Flux pinning and logarithmic relaxation of microwave remanent absorption in superconducting Tl2Ba2Ca2Cu3O10

Abstract We have investigated flux pinning and creep behaviors of Tl-2223 ceramics, measuring microwave remanent absorption as functions of magnetic field and measuring time. When the sample is cooled under larger magnetic field, we find larger remanent absorption after field removal, owing to the flux pinning in the sample. This remanent absorption decays as logarithm of time, from which we have estimated a pinning potential U 0 at 77 K of around 0.5 eV. The potential U 0 has decreased only by a factor of 3, even when the cooling field has increased by two orders of magnitude from 100 to 10000 Oe. Such weak field dependence of U 0 has been related to thermal activation of vortices from intrinsic flux pinning layers in a quasi-two dimensional superconductor.