We report significant intergrain magnetoresistance (IMR) in polycrystalline double perovskites of ${\mathrm{SrFe}}_{\text{1−x}}(\mathrm{Mo or Re}{)}_x{\mathrm{O}}_{\mathrm{3}}$ at room temperature. Systematics of the temperature dependence of IMR indicates that the observed large room-temperature IMR in ${\mathrm{SrFe}}_{\mathrm{1/2}}{\mathrm{Mo}}_{\mathrm{1/2}}{\mathrm{O}}_{\mathrm{3}}$ originates from the ferrimagnetic nature of insulating grain boundaries as well as the half-metallicity of this perovskite. Our results indicate that a new avenue for spin-polarized tunneling junctions is to utilize insulating interface layers with ferromagnetic or ferrimagnetic coupling.

We have performed inelastic neutron scattering on a single crystal sample of ${\mathrm{Sr}}_{14}{\mathrm{Cu}}_{24}{\mathrm{O}}_{41}$ to study the spin dynamics of the ${\mathrm{Cu}}_2{\mathrm{O}}_3$ spin ladder layers and ${\mathrm{CuO}}_2$ chains. Our data are best fitted with a dispersion which has a spin gap of $32.5\pm 0.1\mathrm{meV}$ and a maximum of $193.5\pm 2.4\mathrm{meV}$, consistent with a coupling along the ladders, $J_{\parallel }=130\mathrm{meV}$ and a rung coupling $J_{\perp }=72\mathrm{}\mathrm{meV}$. Excitations with an energy transfer of approximately 11.5 meV arise from a dimer chain with an antiferromagnetic intradimer coupling $J_1=11.2\mathrm{}\mathrm{meV}$ between next-nearest-neighbor Cu ions, and a ferromagnetic interdimer coupling $J_2=-1.1\mathrm{}\mathrm{meV}$. The dimer chains have a periodicity of five units.

Anisotropic electrical resistivity under high pressure was measured for a single crystal of ${\mathrm{Sr}}_{2.5}{\mathrm{Ca}}_{11.5}-{\mathrm{Cu}}_{24}{\mathrm{O}}_{41}$, a hole-doped two-leg ladder compound. Superconductivity was observed between 3.5 and 8 GPa, accompanied by metallic resistivity between the ladders, which indicates semiconducting behavior at ambient pressure. This in turn strongly suggests that the application of pressure brings about a dimensional crossover from one to two, and that superconductivity in this system is a consequence of an insulator to superconductor transition in the anisotropic two-dimensional system.

We measured thermal conductivity $\kappa$, thermoelectric power $S$, and electric conductivity $\sigma$ of ${\mathrm{La}}_{5/8-x}{\mathrm{Pr}}_x{\mathrm{Ca}}_{3/8}{\mathrm{MnO}}_3$, showing an intricate interplay between metallic ferromagnetism (FM) and charge ordering (CO) instability. The change of $\kappa$, $S$, and $\sigma$ with temperature $\left(T\right)$ and $x$ agrees well with the effective medium theories for binary metal-insulator mixtures. This agreement clearly demonstrates that with the variation of $T$ as well as $x$, the relative volumes of FM and CO phases drastically change and percolative metal-insulator transition occurs in the mixture of FM and CO domains.