K. Ramesha

Metallic and nonmetallic double perovskites: a case study of A 2 FeReO 6 (A= Ca, Sr, Ba)

We have investigated the structure and electronic properties of ferrimagnetic double perovskites, {A_2FeReO_6} (A = Ca, Sr, Ba). The A = Ba phase is cubic (Fm3m) and metallic, while the A = Ca phase is monoclinic {P2_1 /n} and nonmetallic. Fe{^57 Mossbauer} spectroscopy shows that iron is present mainly in the high spin S = (5/2) {Fe^3+} state in the Ca compound, while it occurs in an intermediate state between high spin {Fe^2+ and Fe^3+} in the Ba compound. It is argued that a direct {Re t_2g-Re_ t2g} interaction is the main cause for the metallic character of the Ba compound; the smaller size of Ca and the monoclinic distortion (which lifts the degeneracy of {t_2g} states seem to disrupt the Re-Re interaction in the case of the Ca compound, making it nonmetallic for the same electron count.

Investigation of the local fe magnetic moments at the grain boundaries of the Ca2FeReO6 double perovskite

The local Fe ferromagnetic (FM) moment at the grain boundaries of a ceramic sample of Ca2FeReO6 double perovskite was investigated by means of x-ray magnetic circular dichroism spectroscopy at the Fe L-2,L-3 edges and compared to the overall bulk magnetization. We found that, at the grain boundaries, the Fe FM moments at H=5 T are much smaller than expected and that the MxH curve is harder than in the bulk magnetization. These results suggest a larger degree of Fe/Re antisite disorder at the grain boundaries of this sample, shedding light into the intriguing nonmetallic resistivity behavior despite the reported presence of free carriers. (c) 2007 American Institute of Physics.

Crystal structures and magnetic order of La 0.5+δ A 0.5-δ :Mn 0.5+ε Ru 0.5-ε O 3 (A= Ca, Sr, Ba): possible orbital glass ferromagnetic state

K_{2}(NbO)_{2}Si_{4}O_{12}

Crystal structures and magnetic order of La{0.5+delta}A{0.5-delta}Mn{0.5+epsilon}Ru{0.5-epsilon}O{3} (A= Ca, Sr, Ba): Possible orbital glass ferromagnetic state

consisting of trans-connected

Magnetoresistance in the Double Perovskite Sr2CrMoO6

Nb(V)O_{6}

In search of inorganic nonlinear optical materials for second harmonic generation

octahedral chains is a novel nonlinear optical (NLO) material synthesized by Tournoux and coworkers. Our investigation of several inorganic materials containing trans-connected

Spin-orbital ordering and mesoscopic phase separation in the double perovskite Ca 2 FeReO 6

d^0:MO_{6}

Incipient Orbital Order in Half-Metallic Ba2FeReO6

octahedral chains has identified fresnoite

ALaFeVO6 (A=Ca, Sr): New Double-Perovskite Oxides

(Ba_{2}TiOSi_{2}O_{7})