A new class of magnetic materials: Sr2FeMoO6 and related compounds

Ordered double perovskite oxides of the general formula, A2BB'O6, have been known for several decades to have interesting electronic and magnetic properties. However, a recent report of a spectacular negative magnetoresistance effect in a specific member of this family, namely Sr2FeMoO6, has brought this class of compounds under intense scrutiny. It is now believed that the origin of magnetism in this class of compounds is based on a novel kinetically-driven mechanism. This new mechanism is also likely to be responsible for the unusually high temperature ferromagnetism in several other systems, such as dilute magnetic semiconductors, as well as in various half-metallic ferromagnetic systems, such as Heussler alloys.Comment: To appear in Current Opinion in Solid State and Material Scienc

Spin, charge and orbital ordering in La0.5Sr1.5MnO4

We have analyzed the experimental evidence of charge and orbital ordering in La0.5Sr1.5MnO4 using first principles band structure calculations. Our results suggest the presence of two types of Mn sites in the system. One of the Mn sites behaves like an Mn(3+) ion, favoring a Jahn-Teller distortion of the surrounding oxygen atoms, while the distortion around the other is not a simple breathing mode kind. Band structure effects are found to dominate the experimental spectrum for orbital and charge ordering, providing an alternate explanation for the experimentally observed results.Comment: 4 pages + 3 figures; To appear in Phys. Rev. Let

Remarkable thermal stability of BF3-doped polyaniline

We show that the recently synthesized BF3-doped polyaniline (PANI) exhibits remarkable stability against thermal ageing. Unlike the protonated PANI, which shows rapid degradation of the conductivity on heating in air, BF3-doped PANI shows more than an order of magnitude improvement in conductivity. We employ x-ray photoelectron spectroscopy (XPS), fourier transform infra-red (FTIR) spectroscopy, and x-ray diffraction (XRD) to understand this unexpected phenomenon.Comment: 4 pages and 3 figures. To appear in Applied Physics Letters, Sept. 200