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We investigate the origin of the high Neel temperature recently found in Tc perovskites. The electronic structure in the magnetic state of SrTcO3 and its 3d analogue SrMnO3 is calculated within a framework combining band-structure and many-body methods. In agreement with experiment, the Neel temperature of SrTcO3 is found to be four times larger than that of SrMnO3. We show that this is because the Tc-compound lies on the verge of the itinerant-to-localized transition, and also has a larger bandwidth, while the Mn-compound lies deeper into the localized side. For SrTcO3 we predict that the Neel temperature depends weakly on applied pressure, in clear violation of Blochs rule, signaling the complete breakdown of the localized picture.
The microscopic origin of the high Neel temperature (T_N) observed experimentally in SrTcO_3 has been examined using a combination of ab-initio electronic structure calculations and mean-field solutions of a multiband Hubbard model. The G-type antife
We report a systematic study of the $c$ lattice parameter in the Na$_{x}$CoO$_{2}$ phases versus Na content $x>0.5$, in which sodium always displays ordered arrangements. This allows us to single out the first phase which exhibits an AF magnetic orde
A novel frequency dependence of anomaly in dielectric constant versus temperature plot, around the Neel temperature T_N (~150 K), has been observed in a single crystal of bilayer manganite Pr(Sr0.1Ca0.9)2Mn2O7. The anomaly in the permittivity (epsilo
Single crystals of sodium cobaltates Na$_{x}$CoO$_{2}$ with $x approx 0.8$ were grown by the floating zone technique. Using electrochemical Na de-intercalation method we reduced the sodium content in the as-grown crystals down to pure phase with 22 K
We use a quantum Monte Carlo method to calculate the Neel temperature T_N of weakly coupled S=1/2 Heisenberg antiferromagnetic layers consisting of coupled ladders. This system can be tuned to different two-dimensional scaling regimes for T > T_N. In