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The low-temperature crystal structure of a one-dimensional chain-ladder composite material ${\mathrm{Sr}}_{0.4}{\mathrm{Ca}}_{13.6}{\mathrm{Cu}}_{24+y}{\mathrm{O}}_{41+z}$ was determined by the Rietveld analysis of neutron diffraction data using a superspace group approach. The hole distribution between the chain and ladder planes was estimated by the bond-valence sum (BVS) calculation based on Cu-O interatomic distances. The minimum of the distance between ladder-copper and chain-oxygen atoms [Cu(1)\char21{}O(3)] was revealed to expand with lowering temperature. The BVS calculation indicated that such a structural change corresponds to a redistribution of holes from the ladder to the chain and that almost all of the holes are localized in the chain below or near the N\'eel temperature. By assuming reasonable magnetic interactions between hole-unoccupied Cu sites on the chain plane, we propose a possible magnetic structure model taking into account the distribution of holes and observed magnetic neutron Bragg reflections. The results suggest the presence of spin dimers, spin trimers, and ``lone'' spins in the chain, of which the latter two have effective magnetic moments. These moments may be an origin of staggered antiferromagnetic spin modulation onto the spin-liquid state.

We studied structural and electrical properties under high pressure and low temperature for a $S=1/2$ Heisenberg two-leg ladder compound ${\mathrm{Sr}}_{0.4}{\mathrm{Ca}}_{13.6}{\mathrm{Cu}}_{24}{\mathrm{O}}_{41+\mathrm{\ensuremath{\delta}}}.$ It showed a superconducting transition above 3 GPa with a maximum ${T}_{c}$ of 13 K. The ${\mathrm{Sr}}_{0.4}{\mathrm{Ca}}_{13.6}{\mathrm{Cu}}_{24}{\mathrm{O}}_{41+\mathrm{\ensuremath{\delta}}}$ phase survives at least up to 9 GPa and down to 7 K without decomposition or phase transition, indicating that it is responsible for the observed superconductivity. The most important role of high pressure for realizing superconductivity is enhancement of the interaction between the ${\mathrm{Cu}}_{2}{\mathrm{O}}_{3}$ ladder and the one-dimensional ${\mathrm{CuO}}_{2}$ chain which accelerates redistribution of holes via locally formed ${\mathrm{Cu}}_{\mathrm{ladder}}{\ensuremath{-}\mathrm{O}}_{\mathrm{chain}}$ hybrid orbitals. Electrical property of the normal state is affected by the carrier density, dimensionality, random potential, and spin scattering which are related to structural modification under high pressure.

The crystal structure of the newly discovered 117-K superconductor, (Cu,C)${\mathrm{Ba}}_{2}$${\mathrm{Ca}}_{3}$${\mathrm{Cu}}_{4}$${\mathrm{O}}_{11+\mathrm{\ensuremath{\delta}}}$, has been refined from time-of-flight neutron-powder-diffraction data. The structure has ``average'' tetragonal symmetry and is similar to that of Tl(or Hg)${\mathrm{Ba}}_{2}$${\mathrm{Ca}}_{3}$${\mathrm{Cu}}_{4}$${\mathrm{O}}_{\mathit{y}}$. C atoms in ${\mathrm{CO}}_{3}$ groups substitute at the Cu site in the (Cu,C)${\mathrm{O}}_{1+\mathrm{\ensuremath{\delta}}}$ layer leading to a chemical composition of (${\mathrm{Cu}}_{0.68}$${\mathrm{C}}_{0.32}$)${\mathrm{Ba}}_{2}$${\mathrm{Ca}}_{3}$${\mathrm{Cu}}_{4}$${\mathrm{O}}_{11.06}$. This compound has two inequivalent kinds of ${\mathrm{CuO}}_{2}$ layers with pyramidal and square coordination of Cu to oxygen. The inner ${\mathrm{CuO}}_{2}$ layers with Cu in four coordination are less corrugated than the outer ones with Cu in five coordination, and exhibit a structure very similar to those of infinite-layer compounds.

We observed a large decrease in ${T}_{\text{c}}$ by no more than $3\text{ }\text{at}\text{.}\text{ }\mathrm{%}$ of Zn doped into the ${T}_{\text{c}}$-optimized superconductor ${\text{LaFeAsO}}_{0.85}$ $({T}_{\text{c}}=26\text{ }\text{K})$, confirmed by measurements of electrical resistivity, magnetic susceptibility, specific heat, M\"ossbauer spectroscopy, Hall coefficient, and an electron probe microanalysis. The rate $\ensuremath{\sim}9\text{ }\text{K}/\mathrm{%}$ is remarkably higher than others achieved by nonmagnetic impurities. The ${T}_{\text{c}}$ suppression is likely due to pair breaking caused by scattering associated with the highly localized electronic state of Zn in the ${\text{Fe}}_{2}{\text{As}}_{2}$ layer. If this is true, the present result well accords with the theoretical prediction that suggests a sign reversal $s$-wave pairing model for the Fe-pnictide superconductors.

We report on magnetic, resistivity, M\"ossbauer spectroscopy, and scanning tunneling spectroscopy studies of ceramic superconducting (SC) and non-SC $\mathrm{Ru}{\mathrm{Sr}}_{2}{\mathrm{Y}}_{1.5}{\mathrm{Ce}}_{0.5}{\mathrm{Cu}}_{2}{\mathrm{O}}_{10\ensuremath{-}\ensuremath{\delta}}$ $(x=0.5)$ and $\mathrm{Ru}{\mathrm{Sr}}_{2}\mathrm{Y}\mathrm{Ce}{\mathrm{Cu}}_{2}{\mathrm{O}}_{10}$ $(x=1)$. All materials studied were prepared at high oxygen pressure under the same conditions. Two magnetic transitions at ${T}_{2\mathrm{M}}$ and ${T}_{\mathrm{M}}$ $({T}_{2\mathrm{M}}l{T}_{\mathrm{M}})$ are observed. For the SC $x=0.5$ material, both ${T}_{2\mathrm{M}}$ and ${T}_{\mathrm{M}}$ and saturation moments are lower, but its coercive fields are higher as compared to the non-SC $x=0.5$ sample material. In the $x=1$ sample, a dramatic increase in the magnetoresistance occurs at ${T}_{\mathrm{M}}$.

We have investigated magnetic and magneto-optical properties of two-dimensional (2D) ${\mathrm{Ti}}_{0.8}{\mathrm{Co}}_{0.2}{\mathrm{O}}_{2}$ nanosheet, a new nanosized titanium oxide derived from layered titanates by exfoliation. Despite heavy doped 2D system in the dielectric ground, the multilayer films of ${\mathrm{Ti}}_{0.8}{\mathrm{Co}}_{0.2}{\mathrm{O}}_{2}$ nanosheets exhibit room-temperature ferromagnetism with magnetic moment of $1.4{\ensuremath{\mu}}_{B}∕\mathrm{Co}$. We also observe robust magnetic circular dichroism near the absorption edge at $4\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$, indicating a strong spin polarization in this 2D system. The first-principles study of ${\mathrm{Ti}}_{0.8}{\mathrm{Co}}_{0.2}{\mathrm{O}}_{2}$ nanosheet characterizes the ferromagnetic state with a spin-orbit-induced anisotropy.