No abstract

High-precision ellipsoidal mirrors for two-dimensionally focusing X-rays to nanometer sizes have not been realized because of technical problems in their fabrication processes. The objective of the present study is to develop fabrication techniques for ellipsoidal focusing mirrors in the hard-X-ray region. We design an off-axis ellipsoidal mirror for use under total reflection conditions up to the X-ray energy of 8 keV. We fabricate an ellipsoidal mirror with a surface roughness of 0.3 nm RMS (root-mean-square) and a surface figure error height of 3.0 nm RMS by utilizing a surface profiler and surface finishing method developed by us. The focusing properties of the mirror are evaluated at the BL29XUL beamline in SPring-8. A focusing beam size of 270 nm × 360 nm FWHM (full width at half maximum) at an X-ray energy of 7 keV is observed with the use of the knife-edge scanning method. We expect to apply the developed fabrication techniques to construct ellipsoidal nanofocusing mirrors.

This article reviews and discusses the thermodynamic properties of dimer-Mott-type molecular superconductive compounds with (BEDT-TTF) 2 X composition, where BEDT-TTF is bis(ethylenedithio)tetrathiafulvalene and X denotes counter-anions, respectively. We focus mainly on the features occurring in the κ-type structure in which the d-wave superconductive phase appears depending on the Coulomb repulsion U and the bandwidth W, which is tunable by external and chemical pressures. First, we report the high-pressure ac (alternating current) calorimetry technique and experimental system constructed to measure single-crystal samples of molecule-based compounds to derive low-temperature thermodynamic parameters. Using extremely small resistance chips as a heater and a thermometer allows four-terminal detection of an accurate temperature and its oscillation in the sample part with sufficient sensitivity. From the analyses of the temperature dependence of the ac heat capacity of κ-(BEDT-TTF) 2 Cu(NCS) 2 under external pressures, we discuss the changes in the peak shape of the thermal anomaly at the superconductive transition temperature T c at various external pressures p. The rather sharp peak in C p T −1 at T c = 9.1 K with a strong coupling character at ambient pressure is gradually reduced to weaker coupling as the pressure increases to 0.45 GPa concomitant with suppression of the transition temperature. This feature is compared with the systematic argument of the chemical-pressure effect on the basis of thermal anomalies around the superconductive transition of κ-(BEDT-TTF) 2 X compounds and other previously studied typical dimer-Mott 2:1 compounds. Finally, the discussion is extended to the chemical pressure effect on the normal state electronic heat capacity coefficient γ obtained by applying magnetic fields higher than H c2 and the residual γ*, which remains in the superconductive state due to the induced electron density of states around the node structure. From the overall arguments with respect to both chemical and external pressures, we suggest that a crossover of the electronic state inside the superconductive phase occurs and the coupling strength of electron pairs varies from the electron correlation region near the metal-insulator boundary to the band picture region.

We have studied the details of the magnetization reversal process in Ni–Fe nanowires and dots using magnetic field sweeping (MFS)-magnetic force microscopy (MFM). All the points within the nanowire and the dot show important changes in phase (changes in stray field) including a hysteresis loop, a decrease and an increase in phase, as the magnetic field is varied. From these results, it is demonstrated that domain wall motion dominates the magnetization reversal process of a 10-nm-thick Ni–Fe nanowire with widths between 100 and 1000nm. It is also demonstrated that the nucleation, the movement, and the annihilation of the vortex core can be directly observed in the magnetization reversal process of a 40-nm-thick Ni–Fe circular dot with diameters between 200 and 800nm. Furthermore, it is found that, in the magnetization reversal process of a 10-nm-thick Ni–Fe elliptical dot with several major axial distances between adjacent dots, the magnetization between the adjacent dots magnetostatically couples as the major axial distance decreases.

Thermodynamic investigation by calorimetric measurements of the layered organic superconductors, κ-(BEDT-TTF)2Cu[N(CN)2]Br and its partially deuterated compounds of κ-(d[2,2]-BEDT-TTF)2Cu[N(CN)2]Br and κ-(d[3,3]-BEDT-TTF)2Cu[N(CN)2]Br, performed in a wide temperature range is reported. The latter two compounds were located near the metal–insulator boundary in the dimer-Mott phase diagram. From the comparison of the temperature dependences of their heat capacities, we indicated that lattice heat capacities of the partially deuterated compounds were larger than that of the pristine compound below about 40 K. This feature probably related to the lattice softening was discussed also by the sound velocity measurement, in which the dip-like structures of the Δv/v were observed. We also discussed the variation of the electronic heat capacity under magnetic fields. From the heat capacity data at magnetic fields up to 6 T, we evaluated that the normal-state γ value of the partially deuterated compound, κ-(d[3,3]-BEDT-TTF)2Cu[N(CN)2]Br, was about 3.1 mJ K−2 mol−1. Under the magnetic fields higher than 3.0 T, we observed that the magnetic-field insulating state was induced due to the instability of the mid-gap electronic state peculiar for the two-dimensional dimer-Mott system. Even though the volume fraction was much reduced, the heat capacity of κ-(d[3,3]-BEDT-TTF)2Cu[N(CN)2]Br showed a small hump structure probably related to the strong coupling feature of the superconductivity near the boundary.