The magnetic, transport, optical, and structural properties of quasi-one-dimensional BaIrO 3 show evidence for the simultaneous onset of electronic density wave formation and ferromagnetism at T c3 175 K: Two additional features in the chain direction dc conductivity show a sudden change to metallic behavior below T c2 80 K and then a Mott-like transition at T c1 26 K: Highly non-linear dc conductivity, optical gap formation at Ϸ9k B T c3 , additional phonon modes, and emergent X-ray satellite structure support density wave formation. Even at very high (30 T) fields the saturation Ir moment is very small, Ϸ0.04m B /Ir. ᭧ 2000 Elsevier Science Ltd. All rights reserved. Transition metal oxides (TMO) with low crystalline symmetry are known to exhibit electronic density wave formation [1][2][3]. However, to our knowledge, density wave formation has not yet been observed accompanying the onset of ferromagnetic order. However, the ferromagnetism at T c3 175 K in BaIrO 3 [4] appears to be accompanied by and possibly driven by a collective electronic excitation or at least partial gapping of the Fermi surface. This demonstrates once again the strong coupling between spin and charge in the heavy (4d-and 5d-based) TMOs [5][6][7]. BaIrO 3 has a highly anisotropic quasi-one-dimensional structure [8][9][10] and this gives rise, in our single crystal samples, to large anisotropy of r(T), the electrical resistivity, with the quasi-one-dimensional axis, the c-axis, having much lower resistivity. This kind of low-dimensional structure is necessary for the formation of an insulating charge density wave (CDW) ground state, which is a collective electron mode normally incommensurate with the underlying lattice for partially filled bands [3].Evidence for density wave formation comes from: (1) A discontinuous increase in the slope of r (T) vs. T at T c3 T C ; the Curie temperature-an abrupt transition to a more insulating phase. (Two additional features of r (T) along the c-axis, at T c2 80 K and T c1 26 K; mark a sudden return to "metallic" behavior (possibly a crossover from partial toward full gapping of the Fermi surface) and a well-defined Mott-like metal-insulator transition, respectively). (2) An abrupt feature in the non-linear conductivity showing negative differential resistivity. (3) Gap formation at about 1200 cm Ϫ1 in the electron excitation spectrum and a splitting of a phonon mode at 350 cm Ϫ1 , which appear for T Ͻ T c3 (This was determined by optical reflectivity studies in the far and near infrared.). (4) Additional satellite formation for T Ͻ T C3 in the X-ray diffraction spectrum.The structure of BaIrO 3 is monoclinic and consists of Ir 3 O 12 trimers of face-sharing IrO 6 octahedra which are vertex-linked to other trimeric clusters forming columns roughly parallel to the c-axis. These clusters form channels accommodating Ba ions. The space group is C2/m and the

We report a first-order phase transition at T M =357 K in single crystal Ca 2 RuO 4 , an isomorph to the superconductor Sr 2 RuO 4 . The discontinuous decrease in electrical resistivity signals the near destruction of the Mott insulating phase and is triggered by a structural transition from the low temperature orthorhombic to a high temperature tetragonal phase. The magnetic susceptibility, which is temperature dependent but not Curie-like decreases abruptly at T M and becomes less temperature dependent. Unlike most insulator to metal transitions, the system is not magnetically ordered in either phase, though the Mott insulator phase is antiferromagnetic below T N =110 K. PACS: 61.10 Nz, 71.30 +h,

There has been considerable interest in molecular magnets based on the Prussian blue class of transition-metal cyanide complexes.[1] Pioneering work on these materials has realized a broad range of ferro-and ferrimagnetic solids with Curie points ranging from cryogenic to above room temperature. [2,3] A parallel interest also exists in the development of nanocomposite structures containing nanoscale magnetic particles exhibiting single-domain magnetic behavior. [4][5][6] Investigations of magnetic nanocomposites is driven by their novel properties and their potential as new magnetic, optical, and electronic materials. With one exception, [7] however, the Prussian blue class of magnetic materials has not been produced as nanoparticles, and, to the best of our knowledge, there have been no reports of their incorporation into composite structures. Herein we report the fabrication of a new nanocomposite material containingferromagnetic analogue of Prussian blue, in a porous silica matrix. This material is made by a controlled multicomponent sol-gel synthesis in which the precipitation of the Prussian blue analogue is arrested at nanoscale dimensions by gelation of the silica network. The resulting materials are homogeneous, optically transparent, and exhibit superparamagnetic and tunable photomagnetic behavior. We believe that this study suggests a new approach for utilizing the Prussian blue class of magnetic materials in advanced optical and magnetic applications.Homogeneous silica xerogels containing cyanide-bridged Co II /Fe III centers were made by incorporation of both transition-metal components during the solution phase of the synthesis. To obtain homogeneous materials reproducibly, conditions were optimized for the amount of water and the concentration and molar ratio of Co II and ferricyanide by following previously developed procedures. [8,9] In the optimized preparation, Co II nitrate was dissolved in methanol and added to tetramethylorthosilicate. Aqueous potassium ferricyanide was added to this solution to give a 1:1 Co:Fe molar ratio. Upon mixing, the solution turns dark purple, which suggests the formation of the mixed-valence complex. At concentrations up to 0.03 mol % total-metal to silicon (Fe + Co/Si), the solution remained transparent through gelation, aging, and drying, and ultimately yielded a homogeneous, optically transparent xerogel (Figure 1, inset). The spectrum of this glass (Figure 1) is qualitatively similar to that of the bulk materials, with a broad intervalence charge-transfer band in the visible region between 450 and 650 nm and a sharp, higher energy peak around 400 nm. However, the maximum of the intervalence band lies at 452 nm (22 124 cm À1 ) which is blue-shifted by approximately 2900 cm À1 from that of the bulk materials. To determine whether the magnetic behavior was singular, the magnetic susceptibility of these materials was measured as a function of temperature and field strength.[10] Bulk M

Various mechanisms of electrical generation of spin polarization in nonmagnetic materials have been a subject of broad interest for their underlying physics and device potential in spintronics. One such scheme is chirality-induced spin selectivity (CISS), with which structural chirality leads to different electric conductivities for electrons of opposite spins. The resulting effect of spin filtering has been reported for a number of chiral molecules assembled on different surfaces. However, the microscopic origin and transport mechanisms remain controversial. In particular, the fundamental Onsager relation was argued to preclude linear-response detection of CISS by a ferromagnet. Here, we report definitive observation of CISS-induced magnetoconductance in vertical heterojunctions of (Ga,Mn)As/AHPA-L molecules/Au, directly verifying spin filtering by the AHPA-L molecules via spin detection by the (Ga,Mn)As. The pronounced and robust magnetoconductance signals resulting from the use of a magnetic semiconductor enable a rigorous examination of its bias dependence, which shows both linear-and nonlinear-response components. The definitive identification of the linear-response CISS-induced two-terminal spin-valve effect places an important constraint for a viable theory of CISS and its device manifestations. The results present a promising route to spin injection and detection in semiconductors without using any magnetic material.

CsPbBr 3 is a promising type of light-emitting halide perovskite with inorganic composition and desirable thermal stability. The luminescence efficiency of pristine CsPbBr 3 thin films, however, appeared to be limited. In this work, we have demonstrated light emitting diodes based on CsPbBr 3 |Cs 4 PbBr 6 composites. Both quantum efficiency and emission brightness have been improved significantly compared with similar devices constructed using pure CsPbBr 3 . The high brightness can be attributed to the enhanced radiative recombination from CsPbBr 3 crystallites confined in the Cs 4 PbBr 6 host matrix. The unfavorable charge transport property of Cs 4 PbBr 6 can be circumvented by optimizing the ratio between the host and the guest components and the total thickness of the composite thin films. The inorganic composition of the emitting layer also leads to improved device stability under the condition of continuous operation.