Magnetic-history-dependent nanostructural and resistivity changes in Pr0.5Ca0.5Mn0.98Cr0.02O3

We show that nanostructure and resistivity of Pr0.5Ca0.5Mn0.98Cr0.02O3 are sensitive to whether the sample is zero-field-cooled (ZFC) of field-cooled (FC) either in the 'self magnetic field (H = 2 T)' of the electron microscope or under the external magnetic field of 2 T. FC resistivity at H = 2 T is lower than ZFC values below 140 K. The average value of the chare-orbital modulation vector (q = 0.44) of the FC crystallites is lower than that of the ZFC cystallites (q = 0.48) and the FC crystallites exhibit numerous defects like discommensuration, dislocations and regios with loss of superstructures compared to the ZFC crystallites.Comment: 7 pages, 3 figure

Structure determination of a brownmillerite Ca2Co2O5 thin film by Precession Electron Diffraction

Calcium cobaltite thin films with a ratio Ca/Co=1 were grown on (101)-NdGaO3 substrate by the pulsed laser deposition technique. The structure of the deposited metastable phase is solved using a precession electron diffraction 3D dataset recorded from a cross-sectional sample. It is shown that an ordered oxygen-deficient Ca2Co2O5+d perovskite of the brownmillerite-type with lattice parameters a= 0.546nm, b=1.488nm and c=0.546nm (SG: Ibm2) has been stabilized using the substrate induced strain. The structure and microstructure of this metastable cobaltite is further discussed and compared to related bulk materials based on our transmission electron microscopy investigationsComment: 13 pages, 10 figures, 2 tables, accepted in Phys. Rev.

Rhodium Doped Manganites : Ferromagnetism and Metallicity

The possibility to induce ferromagnetism and insulator to metal transitions in small A site cation manganites Ln_{1-x}Ca_xMnO_3 by rhodium doping is shown for the first time. Colossal magnetoresistance (CMR) properties are evidenced for a large compositional range (0.35 \leq x < 0.60). The ability of rhodium to induce such properties is compared to the results obtained by chromium and ruthenium doping. Models are proposed to explain this behavior.Comment: 11 pages, 8 figure