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RESEARCH PRODUCT

Short range charge/orbital ordering in La1−xSrxMn1−zBzO3 (B = Cu,Zn) manganites

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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 ordered domains. The temperature T1 of the phase transition is dependent on the doping concentration and for optimally doped samples we have found that T1 ≈ (0.93 ± 0.02)TC .E lectrical resistivity and magnetization measurements versus temperature and magnetic field support the short range charge/orbital ordering scenario.