X-ray-induced electrical conduction in the insulating phase of thiospinel CuIr2S4

Effects of x-ray irradiation on the crystal structure and the electrical resistance were examined at low temperatures for the insulating phase of spinel compound CuIr2S4. We found that the resistance decreases by more than five decades by irradiation at 8.5 K. The structural change from triclinic to tetragonal was observed at the same time. The x-ray-induced conductance is deduced to result from the destruction of Ir4+ dimers formed in the insulating phase. Slow relaxation of the resistance in the x-ray-induced state is also reported.Comment: 18 pages with 6 figures, pdf format, to be published in Solid State Commu

Large negative magnetoresistance in thiospinel CuCrZrS4

We report on large negative magnetoresistance observed in ferromagnetic thiospinel compound CuCrZrS$_{4}$. Electrical resistivity increased with decreasing temperature according to the form proportional to $\textrm{exp}(T_{0}/T)^{1/2}$, derived from variable range hopping with strong electron-electron interaction. Resistivity under magnetic fields was expressed by the same form with the characteristic temperature T0 decreasing with increasing magnetic field. Magnetoresistance ratio $\rho (T,0)/\rho(T,H)$ is 1.5 at 100 K for H=90 kOe and increases divergently with decreasing temperature reaching 80 at 16 K. Results of magnetization measurements are also presented. Possible mechanism of the large magnetoresistance is discussed.Comment: 9 pages, 5 figures, to be published in Solid State Commu

Metal-insulator transition and superconductivity in the spinel-type Cu(Ir1-xRhx)2S4 system

The normal thiospinel CuIr2S4 exhibits a temperature-induced metal-insulator (M-I) transition around 226 K with structural transformation, showing hysteresis on heating and cooling. It has been verified that d electrons of Ir atom on the octahedral B sites have a significant role for the M-I transition. On the other hand, CuRh2S4 is a superconductor with the transition temperature Tc=4.70 K, which is well understood on the basis of the BCS theory. It is important to investigate the effect on the M-I transition by substitution of Rh for Ir. We have systematically studied structural transformation and electrical and magnetic properties of Cu(Ir1-xRhx)2S4. The features of the M-I transition change with Rh concentration x. A phase diagram of temperature versus x will be proposed for the Cu(Ir1-xRhx)2S4 system. The sharp M-I transition temperature varies drastically from 226 to 93 K with x from 0.00 to 0.17 and disappears around x=0.20. In a region of 0.00⩽x⩽0.20, the magnetic susceptibility begins decreasing at a constant onset temperature 226 K on cooling process and shows rather broad temperature variation, even though the metallic state is kept in the resistivity. The sharp M-I transition can take place after the suppression of magnitude in the susceptibility has sufficiently developed far below 226 K. These experimental results are discussed with emphasis on the intrinsic difference between Cu(Ir1-xRhx)2S4 and CuIr2(S1-xSex)4 systems. Furthermore, we will mention the superconductivity for both systems of Cu(Ir1-xRhx)2S4 with high-Rh concentration region and Cu1-xNixRh2S

Metal-insulator transition in the spinel-type Cu1-xNixIr2S4 system

The normal thiospinel CuIr2S4 exhibits a temperature-induced metal-insulator (M-I) transition around 230 K with structural transformation, showing hysteresis on heating and cooling. The symmetry changes from a high-temperature cubic phase in a metallic state to low-temperature tetragonal phase in an insulating state. A significant characteristic feature is the absence of localized magnetic moment below TM-I. On the other hand, NiIr2S4 remains metallic down to 4.2 K without the structural transformation. We have systematically studied the structural transformation and electrical and magnetic properties of Cu1-xNixIr2S4. The variation of the metal-insulator transition with Ni concentration x is presented. A phase diagram between TM-I and x will be provided for the Cu1-xNixIr2S4 system. The TM-I varies drastically from 226 to 88 K with x from 0.00 to 0.13 and disappears around x=0.15. For 0.08&les;x&les;0.13, the cubic and tetragonal phases coexist below TM-I. For a high-temperature metallic phase, the value of the Pauli paramagnetic susceptibility increases monotonically with x, which shows dD(&epsiv;)/d&epsiv;<0 at the Fermi energy &epsiv;F, through the decrease of the free-electron number density, where D(&epsiv;) is the electronic density-of-state on the basis of a nearly free-electron model. By the introduction of a Ni ion to the A-site of CuIr2S4 in the spinel structure, whether the localized magnetic moment below TM-I arises or not will be discusse

Metal-insulator transition in the spinel-type CuIr2(S1-xSex)4 system

The thiospinel CuIr2S4 exhibits a temperature-induced metal-insulator (M-I) transition around 226 K, showing hysteresis on heating and cooling, that manifests itself as a gap in the electronic density of state with increasing electrical resistivity at low temperatures. Conversely, CuIr2Se4 remains metallic down to 0.5 K. We have successfully synthesized the spinel-type compound CuIr2(S1-xSex)4 system. In order to see the effect of substitutions of Se at the S sites, we have carried out a systematic experimental study of structural, electrical, and magnetic properties of CuIr2(S1-xSex)4. Mössbauer spectroscopy measurements of 193Ir have been performed for CuIr2S4 and CuIr2Se4. The M-I transition of CuIr2(S1-xSex)4 for x&les;0.15 is accompanied by a structural transformation from tetragonal (low-temperature insulating phase) to cubic (high-temperature metallic phase) symmetry. With increasing Se concentration x, the sharp M-I transition shifts to lower temperature. The resistivity shows a monotonous increase with decreasing temperature for 0.17&les;x&les;0.78 between 4.2 and 300 K, and the metallic state is recovered for x&ges;0.80. Magnetic susceptibility measurements show the jump at the M-I transition temperature with hysteresis on heating and cooling. The high-temperature metallic phase of CuIr2S4 shows Pauli paramagnetism, having a density of states at the Fermi level, D(&epsiv;F)=0.67 states/eV atom. The insulating phase at low temperatures exhibits diamagnetism, and there is no localized magnetic moment. The Arrhenius regime is observed for the conductivity with a thermally activated process for 0&les;x&les;0.70 in the insulating phase. There is a general trend toward increasing metallicity with increasing x, which is consistent with the magnetic susceptibility results. A possibility of a two-site model of different valence states for Ir ions in the insulating phase of CuIr2S4 will be discussed on the basis of the Mössbauer data. A phase diagram of temperature versus Se concentration x will be proposed for the CuIr2(S1-xSex)4 system. The mechanism of the M-I transition remains enigmatic and is far from a complete pictur

Mossbauer studies on FeSe and FeTe

We carried out 57Fe Mossbauer measurements for FeSe and Fe1.08Te to investigate the magnetic properties. There was no sign of magnetic ordering above 4.2 K for superconducting FeSe. The magnetic sextet corresponding to antiferromagnetic ordering of Fe in low-spin state was observed for non-superconducting Fe1.08Te.Comment: 5 pages, 2 figures, proceedings of M2S conferenc

Liquid-based urine cytology as a tool for detection of human papillomavirus, Mycoplasma spp., and Ureaplasma spp. in men

金沢大学医薬保健研究域医学系Liquid-based urine cytology (LB-URC) was evaluated for cytological diagnosis and detection of human papillomavirus (HPV), Mycoplasma, and Ureaplasma. Midstream urine samples were collected from 141 male patients with urethritis and 154 controls without urethritis, and sediment cells were preserved in liquid-based cytology solution. Urethral swabs from urethritis patients were tested for the presence of Neisseria gonorrhoeae and Chlamydia trachomatis. Papanicolaou tests were performed for cytological evaluation. HPV, Mycoplasma, and Ureaplasma genomes were determined by PCR-based methods, and localization of HPV DNA in urothelial cells was examined by in situ hybridization (ISH). The β-globin gene was positive in 97.9% of LB-URC samples from urethritis patients and in 97.4% of control samples, suggesting that high-quality cellular DNA was obtained from the LB-URC samples. HPV DNA was detected in 29 (21.0%) urethritis cases and in five (3.3%) controls (P<0.05). HPV type 16 (HPV 16) was most commonly found in urethritis patients. Cytological evaluations could be performed for 92.1% of urethritis patients and 64.3% of controls. Morphological changes suggestive of HPV infection were seen in 20.7% of the HPV-positive samples, and ISH demonstrated the presence of HPV DNA in both squamous and urothelial cells in HPV-positive samples. Mycoplasma genitalium, Mycoplasma hominis, Ureaplasma parvum, and Ureaplasma urealyticum were detected in 14.5%, 10.9%, 6.5%, and 12.3% of urethritis patients, respectively. The prevalence rates of these microorganisms (except Ureaplasma parvum) were significantly higher in urethritis cases than controls (P<0.05). LB-URC is applicable for detection of HPV, Mycoplasma, and Ureaplasma. HP infection occurs in urothelial cells, especially in gonococcal urethritis. Copyright © 2012, American Society for Microbiology. All Rights Reserved