Kimihito Tagaya

ESR of CuO Particles in a Bi2(Sr, Ca)3Cu2Oy Crystal

ESR measurements were performed at the X-band for a Bi2(Sr, Ca)3Cu2Oy crystal over the temperature range from 77 K to room temperature, and a clear ESR line of superparamagnetic particles of CuO was observed with the external field of ca. 3 kOe. The resonance field of the absorption peak became a minimum at 230 K, at which point the absorption intensity became a maximum. Furthermore, an anisotropy of the resonance field was observed for another broad absorption. Possible interpretations for the results are discussed in terms of magnetic anisotropies in CuO particles.

ESR study of Gd2BaCuO5

Abstract An ESR study was performed on bulk and powder specimens of Gd 2 BaCuO 5 in the temperature range from 77 to 473 K. Gd 3+ spins exhibit paramagnetic properties above the Neel temperature of 12 K, but Cu 2+ spins exhibit weak antiferromagnetic order even at room temperature. Superparamagnetism of Cu 2+ appears in powder specimens with particle dimensions of several μm. The magnetic susceptibilities of Gd 3+ and Cu 2+ were determined separately. Further, Gd 3+ and Cu 2+ spins interact weakly with each other. The temperature variation of the susceptibility of Gd 3+ deviates a little from that in a Curie-Weiss law.

Superconductivity of the Pb-3212 compound in the Pb–Sr–La–Cu–O system and resistivity of the compound substituted by Ca

Abstract Superconducting phase with an onset near 60 K has been discovered in the Pb 2 Sr 3− x La x Cu 3 O z system without Ag-doping. The optimum superconducting onset is obtained for a sample with the nominal composition of Pb 2 Sr 2.5 La 0.5 Cu 3 O z . From X-ray diffraction and magnetic susceptibility measurements, it becomes clear that superconductivity results from the Pb-3212 phase, though the sample is not of the single phase. Then, almost the single 3212-phase sample and the samples substituted by Ca are obtained, but they are all semiconductors. The temperature dependences of the resistivity for these samples suggest that the transport process is followed by a three-dimensional variable range hopping conduction.

Synthesis of Ce-Free Pb-3222 Compound in the Pb-Sr-La-Gd-Cu-O System

It has been found that the Pb-3222 phase sample could been synthesized in Ce-free Pb-Sr-La-Gd-Cu-O system and the nearly single-phase samples can be obtained within a limited composition. Then, among the nearly single-phase samples, a sample with a nominal composition of Pb2Sr1.4La0.7Gd1.9Cu3Oz shows a diamagnetic signal with an onset around 20 K. The superconducting behavior is supposed to arise from the Pb-3222 phase.

Microwave magnetoabsorptions of Bi2(Ca,Gd,Bi)3Cu2Oz superconductor

Abstract Microwave magnetoabsorptions were observed for a Bi2(Ca,Gd,Bi)3Cu2Oz superconductor over a temperature range from 6 K to room temperature. A broad absorption slope of Gd3+ was observed with the external static field from 0 to 6 kOe, because a weak antiferromagnetic order occurred in the Gd3+ sublattice. When each particle is small in a powder specimen, a usual ESR line of Gd3+ was observed due to superparamagnetism. Nonresonant microwave absorptions due to superconductivity were observed below 56 K, and the lower critical field as well as the diamagnetic susceptibilities were determined.

Microwave magnetoabsorptions of ErBa2Cu3Oy and HoBa2Cu3Oy single crystals

Abstract Microwave magnetoabsorption measurements were performed for single crystals of ErBa 2 Cu 3 O y and HoBa 2 Cu 3 O y in a temperature range from 3 to 80 K. Microwave magnetoabsorptions due to superconductivity were observed, and the principal values of the lower critical field were determined as 140 or 150 ± 10 Oe and 430 ± 10 Oe at 5 K for the ab -plane and the c -axis, respectively. Their temperature variations were investigated. Further, ESR signals of Er 2 BaCuO 5 and Ho 2 BaCuO 5 were observed, and their superparamagnetic properties were investigated.

Lower Critical Fields in Bi-2212 and Bi-2223 Superconductors

Low-field microwave magnetoabsorptions were observed for Bi-2212 and Bi-2223 specimens, and the lower critical fields were investigated. The principal values of Hc1 were determined over a temperature range from 4 to 60 K. Their temperature variations may be related to the low dimensional character of superconductivity.

Nonresonant microwave absorptions of Ln-123, Bi-2212 superconductors

Abstract Nonresonant microwave absorptions were observed for Ln-123 (Ln=Sm,Gd,Tm), Bi-2223 and Bi-2212 superconductors at 77 K. An abrupt change in a low-field range was analyzed, and the principal values of lower critical field were determined.

ESR and Nonresonant Microwave Absorption of ErBa2Cu3O7-δ and HoBa2Cu3O7-δ Single Crystals

ESR measurements were performed for ErBa2Cu3O7-δ and HoBa2Cu3O7-δ single crystals from 77 K to room temperature. The ESR signals of Er2BaCuO5 and Ho2BaCuO5 were observed, and their temperature variations were investigated. A nonresonant microwave absorption was also observed below the superconducting critical temperature of 93 K, and was investigated. The principal values of lower critical field were determined.

ESR Study of BiSrCaCu2Ox

ESR measurements were performed for BiSrCaCu2Ox ceramics over the temperature range from 77 K to room temperature. From the broad microwave absorption, the Meissner effect was observed for a superconducting specimen, and the lower critical field of the high-Tc phase was determined to be 22 Oe at 77 K. After the specimen was heat-treated at 950°C in air, the Meissner effect became weak, and an ESR signal was observed due to precipitated CuO particles, which exhibited a superparamagnetism. A broad absorption of Cu2O was also observed for a specimen heated at 1050°C in air and then quenched.