0000000000423832
AUTHOR
N. Paunović
Influence of Mn site doping on electrical resistivity of polycrystalline La1-yAyMn1-xBxO3 (A=Ba, Sr; B=Cu, Cr, Co) Manganites
We have the measured electrical resistivity of La1-yBayMn1-xCuxO3 (0.17?y?0.30; 0.04?x?0.10), La1-ySryMn1-xCrxO3 and La1-ySryMn1-xCoxO3 (0.270?y?0.294; 0.02?x?0.10) polycrystalline samples in the 25-325 K temperature range. The increase of Mn site doping concentration leads to an increase of the electrical resistivity of the samples and the appearance of a ?double-peak? structure in the electrical resistivity versus temperature graphs. The first peak represents the insulator-metal transition in vicinity of the paramagnetic-ferromagnetic transition (TC). We have found that the intensity of the second peak increases with an increase of concentration of Mn substituents, due to the hole scatter…
Short range charge/orbital ordering in La1−xSrxMn1−zBzO3 (B = Cu,Zn) manganites
We have measured the reflectivity spectra of La1−x SrxMn1−zBzO3 (B = Cu, Zn; 0.17 x 0.30; 0 z 0.10) manganites over wide frequency (100–4000 cm −1 )a nd temperature (80–300 K) ranges. Besides the previously observed infrared active modes or mode pairs at about 160 cm −1 (external mode), 350 cm −1 (bond bending mode) and 590 cm −1 (bond stretching mode), we have clearly observed two additional phonon modes at about 645 and 720 cm −1 below the temperature T1 (T1 < TC), which coincides with the phase transition temperature when the system transforms from ferromagnetic metallic into a ferromagnetic insulator state. This transition is related to the formation of short range charge/orbitally orde…
Novel phase transitions in B-site doped manganites
We have examined the infrared reflectivity and the electrical resistivity of La 1-x [Sr(Ba)] x Mn 1-z [Cu(Zn)] z O 3 samples in ferromagnetic metallic and insulator regime. Several phase transitions are observed, the most obvious being the transition from a ferromagnetic metallic to a ferromagnetic insulator phase that is related to the formation of short-range orbitally ordered domains. The temperature T 1 of the phase transition is dependent on doping concentration and for optimally doped samples (∼32% of Mn 4+ ions) we have found T 1 0.93 T C .
Effect ofA-site andB-site substitution on the infrared reflectivity spectra ofLa1−yAyMn1−xBxO3(A=Ba,Sr;B=Cu,Zn,Sc;0<y<~0.3;0<~x<~0.1)manganites
We have measured the infrared reflectivity spectra of ${\mathrm{La}}_{1\ensuremath{-}y}[\mathrm{Sr}(\mathrm{Ba}){]}_{y}{\mathrm{Mn}}_{1\ensuremath{-}x}[\mathrm{Cu}(\mathrm{Zn},\mathrm{Sc}){]}_{x}{\mathrm{O}}_{3}$ $(0lyl~0.3,0l~xl~0.10)$ manganites, in a wide frequency $(100\char21{}4000{\mathrm{cm}}^{\ensuremath{-}1})$ and temperature (80 K\char21{}300 K) range. The reflectivity spectra were analyzed by a fitting procedure based on a model that includes Drude, midinfrared electronic, and phonon oscillator contributions to the dielectric constant. Six infrared active ${(3A}_{u}$ and ${3E}_{u})$ modes of rhombohedral symmetry are clearly observed. We assigned all observed modes according to e…